Lab-on-a-chip devices for global health: Past studies and futureopportunities

Curtis D. Chin,a Vincent Linderb and Samuel K. Sia*a

Received 8th August 2006, Accepted 10th October 2006

First published as an Advance Article on the web 27th October 2006

DOI: 10.1039/b611455e

A rapidly emerging field in lab-on-a-chip (LOC) research is the development of devices to

improve the health of people in developing countries. In this review, we identify diseases

that are most in need of new health technologies, discuss special design criteria for LOC

devices to be deployed in a variety of resource-poor settings, and review past research into

LOC devices for global health. We focus mainly on diagnostics, the nearest-term application

in this field.

1. Introduction

Lab-on-a-chip (LOC) technologies have a tremendous but

unproven potential to improve the health of people in

developing countries. Ever since the modern inception of

LOC and microfluidic technologies around 1990, use in remote

settings has been perceived as potentially one of the most

powerful applications of the technology by taking advantage

of its small size, low volume requirement for samples, and rapid

analysis. Indeed, portable LOC devices are now beginning to

be used in remote settings, as a result of developments in

integrating fluid actuation, sample pre-treatment, sample

separation, signal amplification, and signal detection into

a single device. As they stand, these devices are not yet

appropriate for use in the extreme resource-poor settings of

developing countries; nevertheless, these advances place the

field of LOC research in a prime position to tackle the

profound issue of global health, where the challenges in device

designs are arguably the most demanding, and the need for

new health technologies the greatest.

There is an urgent need in developing countries for new

health-related technologies, and specifically, new technologies

for health diagnostics. For example, in one survey of

international scientists familiar with the public health pro-

grams of developing countries, Singer and colleagues found

that the top-ranking overall priority was ‘‘modified molecular

technologies for affordable, simple diagnosis of infectious

diseases’’.1 Similarly, in a study by the Bill and Melinda Gates

Foundation and the NIH to identify ‘Grand Challenges for

Global Health’, two of the 14 priorities involved diagnosis

and measurement of patients’ health statuses (i.e. ‘‘develop

technologies that allow assessment of individuals for multiple

conditions or pathogens at point-of-care’’, and ‘‘develop

technologies that permit quantitative assessment of population

health status’’).2 LOC research holds substantial potential for

fulfilling these priorities by automating complex diagnostic

procedures that are normally performed in a centralized

laboratory into a hand-held microfluidic chip; this capability

could empower health-care workers and patients with impor-

tant health-related information in even the most remote

settings. To this effect, funding by philanthropic foundations

(such as those from Doris Duke, Soros, and Gates) are leading

the development of microfluidics technologies for diagnostics

in developing countries. The broad aim of these scientific

initiatives is to combine new diagnostic and prevention

methods with treatment to improve public health,3 which is

in turn linked closely to the macroeconomic health of a

nation.4

In this review, we aim to aid interested scientists and

engineers by systematically reviewing the fledgling field of

LOC devices for global health. We will focus mainly on

diagnostics, the nearest-term application of LOC devices,

although we will also discuss other applications. We will first

identify the most critical health conditions and diseases that

are in need of new diagnostic methods, with an emphasis on

those in need of new LOC diagnostic devices (Section 2). In

subsequent sections, we will discuss the special design criteria

that are needed for LOC devices to be deployed in developing

aDepartment of Biomedical Engineering, Columbia University, 351Engineering Terrace, 1210 Amsterdam Avenue, New York, NY 10027,USA. E-mail: ss2735@columbia.edubSAMLAB, Institute of Microtechnology, University of Neuchatel, RueJaquet-Droz 1, P. O. Box 526, CH-2002 Neuchatel, Switzerland

Curtis Chin is a PhD student in the Department of BiomedicalEngineering at Columbia University. He obtained his BS inChemical Engineering from the Massachusetts Institute ofTechnology.

Vincent Linder, PhD, is a research scientist at the University ofNeuchatel and Claros Diagnostics. He holds a MSc inChemistry and a PhD in Sciences from the University ofNeuchatel (Switzerland), where he worked on microfluidictechnology for immunoassays. He completed his postdoctoralwork in the Department of Chemistry at Harvard University.

Samuel Sia, PhD, is an Assistant Professor of BiomedicalEngineering at Columbia University. He holds a BS inBiochemistry from the University of Alberta (Canada), and aPhD in Biophysics from Harvard University. He completed hispostdoctoral work in the Department of Chemistry at HarvardUniversity.

CRITICAL REVIEW www.rsc.org/loc | Lab on a Chip

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 41

countries (Section 3), and provide a review of past and current

studies on LOC devices for global health, as well as examples

of LOC devices that have not been—but could be—applied to

these settings (Section 4). We will conclude with a summary

and future directions (Section 5). Throughout the review, we

will identify examples of past research, current promising

technologies, and future challenges and opportunities.

2. Current need for diagnostic devices in developingcountries

In developed and developing countries alike, early and

accurate diagnosis is important for the health of individual

patients as well as that of the general public: it permits prompt

and proper treatment of patients, limits the spread of disease in

the population, and minimizes the waste of public resources on

ineffective treatments.1 In developing countries, the value of

diagnosis for certain diseases is sometimes mitigated by the

lack of available treatment (for example, in cases of certain

neglected tropical diseases). On the whole, however, the value

of diagnosis is very high in developing countries: early

diagnosis, although not without logistical hurdles, can often

lead to some kind of treatment (either directly against the

condition or at worst palliative care), and investments in

diagnostics and prevention can be more cost-effective than

treatment.5 Moreover, point-of-care devices can improve the

epidemiological surveillance of diseases,6 which is an especially

challenging problem in developing countries.

For scientists and engineers who aim to design new

diagnostic technologies, a crucial question for achieving real-

world impact is which health conditions in developing

countries are most in need of diagnostic devices. In a study

led by Murray and Lopez, the World Health Organization

conducted an unprecedented and comprehensive initiative

to compile statistics for comparing the relative burden of

diseases, conditions, injuries, and risk factors on a global

scale.7–9 In Table 1, we list the most common diseases by

disability-adjusted life years (DALYs) in developing countries,

a metric that accounts for years of life lost due to premature

mortality as well as disability (in order to properly account for

the impact of conditions that cause significant ill health but

few direct deaths, such as neuropsychiatric conditions9,10).

As expected,10 infectious diseases constitute a large burden

of disease in developing countries (32.1%; by comparison, they

represent only 3.7% of total DALYs in developed countries).

The trifecta of HIV/AIDS, malaria, and tuberculosis (TB),

which has merited a dedicated focus from the international

community (most notably the Global Fund, which has thus far

committed $5.5 billion, www.theglobalfund.org), constitutes

an important 12% of DALYs in developing countries. The

social impact of these diseases stretches beyond the DALY

statistics, however, since HIV/AIDS (along with common

coinfections of TB) targets healthy adults, thereby leaving

behind villages of orphans which destroy the underlying

fabric of entire communities. Other infectious diseases are

also important. Most significantly, lower respiratory infections

and diarrheal diseases (such as rotavirus and cholera)

impose large burdens; these diseases are also the biggest

killers of children,10 even more so than vaccine-treatable

childhood-cluster diseases (such as diphtheria, measles,

pertussis, and tetanus). Another important category of infec-

tious diseases is neglected tropical diseases (which includes

lymphatic filiariasis, dengue, Chagas disease, leishmaniasis,

onchocerciasis, schistosomiasis, trypanosomiasis, trachoma,

and guinea worm), which cause 500 000 deaths annually.

Although they do not contribute as significantly as some other

infectious diseases by the measure of DALYs in the Global

Burden of Disease report, the real burden of disease is likely to

be higher than these estimates, with up to 90% of the burden

concentrated in sub-Saharan Africa (for example, there are

200 million cases of hookworm infections in Africa alone).11

Current methods for diagnosing neglected diseases are

cumbersome, invasive, and largely inadequate (e.g. for human

African typanosomiasis and visceral leishmaniasis, see ref. 12),

a consequence of the low priority given to neglected diseases

for research funding (as pointed out poignantly by studies such

as the 10/90 Report on Health Research, www.globalforum-

health.org, and ref. 13). In one analysis to define priorities for

diagnostics development, Mabey and colleagues charted the

need versus feasibility for selected diseases (including many

neglected diseases), with the conclusion that African trypano-

somiasis, visceral leishmaniasis, and TB are three of the tests

most in need of development.14 Other important diseases

include sexually-transmitted infections other than HIV/AIDS

(such as hepatitis B and C, chlamydia, gonorrhea, and

syphilis), some of which (most notably, hepatitis B and C,

and HIV) are bloodborne pathogens that can also be

transmitted by contaminated needles as well as contaminated

blood supply for transfusions.15

Like infectious diseases, the burden of non-communicable

diseases is significant (at 43.5% DALY, it even exceeds that of

infectious diseases by a large margin) (Table 1); unlike

infectious diseases, the burden of non-communicable diseases

in developing countries is often underappreciated.16 The

specific list of important non-communicable diseases is

familiar to readers from Western countries: cardiovascular

disease (such as ischaemic heart disease and stroke), cancer,

neuropsychiatric conditions (such as unipolar depressive

disorder), and respiratory diseases (such as chronic obstructive

pulmonary disorder and asthma). As the standard of living in

developing countries improves and average life span increases,

the burden of disease will gradually shift to the non-

communicable diseases; this shift is exacerbated by changes

in diet (towards saturated fats and sugars) and high tobacco

use.16 Already, obesity and diabetes are increasingly prevalent

in developing countries.17 Even for children in developing

countries, asthma, epilepsy, dental caries, diabetes, rheumatic

heart disease, and injuries are becoming increasingly promi-

nent contributors to morbidity.18 As these trends develop,

accessibility of the corresponding diagnostic technologies in

developing countries cannot be assumed from their likely

availability in Western countries, due to the special constraints

of resource-poor settings (see Section 3).

Maternal, perinatal and nutritional diseases contribute a

significant fraction of DALYs (11.8%) in developing

countries (Table 1). Two important risk factors for material

diseases include anemia and vitamin A deficiency;10 although

treatment is the most important consideration for these two

42 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

micronutrient deficiencies, diagnosis can lead to improved

epidemiological surveillance. Overall, malnutrition is the single

most important cause of loss in global health, with the greatest

effect felt in sub-Saharan Africa.10 To combat malnutrition in

children under five years of age, a simple bracelet made by

Medicins Sans Frontieres can be used to measure the mid

upper-arm circumference in order to diagnose the stage of

malnourishment; biochemical measurements may be useful for

more specific diagnoses (e.g. serum albumin levels for protein-

energy malnutrition).

Finally, intentional and unintentional injuries (including

war) constitute a significant DALY fraction (12.5%) that rivals

Table 1 Important diseases in developing countries, burden of disease, diagnostic assays, and corresponding potential LOC devices

Diseasea%DALYb Type of assayc Device Disease

%DALY Type of assay Device

Communicable diseases 32.1 Non-communicable diseases 43.5Respiratory infect.

(lower, upper,ottis media)

6.8 IA Sec. 4.2 Neuropsychiatric conditions(unipol & bipol deprs,others)

11.7 Sx/Hx/PE N/ASlide agg. w/antisera Sec. 4.2 Hormone levels Sec. 4.5GS and cul. of CSF Sec. 4.4

HIV/AIDS 6.1 IA for a-HIV Ab(¡ vs quant)

Sec. 4.2 Cardiovascular diseases (isc.,hyp., rheum., inflamm.)

9.5 ELISA of CRP, BNPCholesterol test

Sec. 4.2Sec. 4.5

RT-PCR for HIV RNA Sec. 4.3 Sense order diseases (cataracts,hearing loss, glaucoma)

4.6 Sx/Hx/PE N/ACD4+ counts Sec. 4.4

Diarrheal diseases(rotavirus,cholera)

4.5 EIA Sec. 4.2 Cancer 4.2 IA of biomarkers(e.g. PSA)

Sec. 4.2Latex agg. assay of stool Sec. 4.2RT-PCR Sec. 4.3 Gene expression Sec. 4.3

Malaria 3.4 Mic. of blood smears Sec. 4.4IC test for HRP-2,

LDH, PSSec. 4.2

Respiratory diseases (COPD,asthma, others)

3.5 SpirometrySx/Hx/PE

N/AN/A

PCR for plasmodium Sec. 4.3Digestive diseases (liver

cirrhosis, peptic ulcerdisease)

3.0 Complete blood count Sec. 4.4

Tuberculosis 2.5 Tuberculin skin test N/AElectrolytes, creatinine Sec. 4.5

Mic. and sputum culture Sec. 4.4Elevated liver enzymes Sec. 4.2

Release of IFN-cfrom blood

Sec. 4.2Congenital abnormalities

(heart dis., DS)1.9 Karyotype analysis

trisomy 21N/A

Measles 1.6 Virus isolation Sec. 4.3RBC count Sec. 4.5

Monitor specific IgG titers Sec. 4.2Sx/Hx/PE N/A

IA for virus (MV) IgM Sec. 4.2Musculoskeletal dis.

(osteoarthritis,rheumatoid arthritis)

Genitourinary dis. (neph.,bphyp.)

1.8

1.0

Differential WBC Sec. 4.4

Pertussis

Tetanus

0.9

0.5

PCR of nasal secretionsCultureCultureIA

Sec. 4.3Sec. 4.4Sec. 4.4Sec. 4.2

ELISA rheumatoidfactor

Sx/Hx/PE (physician)

Sec. 4.2

N/A

Meningitis 0.4 CSF glucose Sec. 4.5Diabetes mellitus 1.0 Plasma/glucose test Sec. 4.5

CSF cell count Sec. 4.4Insulin Sec. 4.2

GS & cul. of CS Sec. 4.4Endocrine disorders 0.5 Hormone levels Sec. 4.5

Lymphatic filariasis

Hepatitis B &hepatitis C

0.4

0.3

ELISA Sec. 4.2X-rays, radiological

examsN/A

IC test of W. bancrofti Sec. 4.2Mic. blood samples

midnightIA HBsAg, anti-HBs,

antiHBc

Sec. 4.4

Sec. 4.2

Oral conditions (dental caries,edentulism, others)

Skin diseases

0.5

0.3

Sx/Hx/PE (dentist)X-rays, radiological

examsSx/Hx/PE (physician)

N/AN/A

N/A

IA liver enzyme, AFP Sec. 4.2 Maternal, perinatal, andnutritional conditions

11.8HCV detection &

genotyingSec. 4.3

Perinatal cond. (LW., BA.,trauma)

7.0 Sx/Hx/PE (physician) N/ASyphilis 0.3 VDRL Sec. 4.2

Nutritional deficiencies(protein-energy, Fe-anaemia)

2.4 IA albumin Sec. 4.2RPR Sec. 4.2Cell count anemia Sec. 4.4FTA-ABS of TPHA Sec. 4.2

Maternal cond. (hem.,seps., hypertens.)

2.4 Haemotology Sec. 4.4–5Chlamydia 0.3 PCR from urine dipstick Sec. 4.3ELISA of C. trachomatis

antigensSec. 4.2

Injuries 12.5NAAT, hybridization test Sec. 4.3Unintentional injuries (RA,

falls, fires, dr.)9.2 Analytical toxicology Sec. 4.2,5Gonorrhea 0.2 Mic & cul. urethral cervical Sec. 4.4

Intentional injuries (violence,SII, war)

3.3 Culture (eg. C. tetani) Sec. 4.4Trachoma 0.2 Culture Sec. 4.4

IA Sec. 4.2Antigen detection Sec. 4.2

Leishmaniasis 0.2IC test Sec. 4.2Mic. & cul. spleen, bone

marrowSec. 4.4

Trypanosomiasis &schistosomiasis

0.2 Agg. test for IgM, PCRparasite

Sec. 4.2–3

Mic. & cul. spleen, bonemarrow

Sec. 4.4

Intestinal nematodeinfect.

0.2 Mic. & cul. anal swab Sec. 4.4

Japaneseencephalitis

0.1 IA of blood andspinal fluid

Sec. 4.2

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 43

that of other categories, and which is higher than that in

Western countries (9.1%) (Table 1). A number of behavioral

changes can be undertaken for preventing injuries in develop-

ing countries.19 From the perspective of diagnostic devices, this

burden may call for devices for detecting poisons, diagnosing

neuropsychiatric conditions (such as epilepsy) and substance

of abuse to ensure prompt treatment, and diagnosing tetanus

infections to strengthen epidemiological surveillance.

To diagnose this wide array of diseases and conditions,

assays with a variety of methodologies will be needed. The

types of assays that are currently used to diagnose them are

listed in Table 1; some assays are in great need of new

diagnostic methods, and some are not. For each diagnostic

assay, potential corresponding LOC devices are also listed.

Analysis of this table, which cross-lists diseases and techno-

logies, reveals a couple of points. (1) Similar classes of analytes

(e.g. proteins, nucleic acids) serve as useful markers for very

different diseases and conditions; hence, similar designs of

diagnostic technologies will be applicable for disparate classes

of diseases. (For example, yes/no protein markers are useful

for diagnosis of HIV/AIDS as well as indicators of coronary

heart disease). In Section 4, we will review potential LOC

technologies as grouped by analytes. (2) Multiple classes of

assay technologies are needed to produce complete diagnostic

information for groups of related diseases, and often even for

a single disease (for confirmatory testing, identification of

resistant subtypes, and/or staging of a disease). (For example,

yes/no testing for antibodies, analysis of RNA levels, and

counting of CD4+ lymphocytes are all crucial information for

diagnosing and staging HIV/AIDS.) This observation calls for

carefully considering the integration of multiple modular

technologies at the earliest design stages of LOC diagnostic

devices for developing countries.

3. Third-world design constraints

Like no other setting, the use of LOC devices in developing

countries poses a set of extremely challenging design criteria.

For maximum range of use, a LOC device would have to

perform reliably under the well-documented constraints of low

cost, absence of trained workers, lack of electricity, poorly

equipped laboratories, and transportation and storage in

unrefrigerated conditions with rough handling.14 In practice,

however, not all of these constraints apply to all settings in

developing countries. For example, in developing countries,

different design criteria apply to centralized testing in a

national laboratory, in a rural health clinic, and in a remote

setting with no infrastructure (Table 2). Similarly, there exist

subtle but important distinctions in the constraints. For ‘low

cost’, the economics of centralized testing may allow for the

purchase of a moderately priced or even expensive fixed

instrument (tens of thousands of dollars), if the cost of

disposables is kept sufficiently low. By contrast, remote point-

of-care testing requires low cost in both the fixed instrument

and the disposable (pennies). Since these considerations hold

direct pertinence to the design of the diagnostic technology, it

is beneficial to be aware of the final targeted use of the device

at the earliest design stages. For example, in the extreme points

of the landscape of resource availability in developing

countries, devices targeted for national centralized laboratories

may include currently available technologies for Western

countries (e.g. 96 well plate assays using an expensive and

bulky fluid-handling machine and detector), and devices for

point-of-care testing in rural settings will need to be designed

with all of the constraints in mind.

In the centralized laboratories of Western countries (run by

companies such as Quest Diagnostics as well as in-house

centers in hospitals) with skilled personnel, established

infrastructure, and high financial resources, sophisticated tests

such as microscopy, ELISAs, and nucleic acid amplification

tests are routinely performed (Table 2).14 Although it would be

desirable for diagnostic tests in this setting to meet criteria such

as rapid analysis to improve efficiency of operation, there exist

few constraints (compared to other settings for diagnostics)

that result from low capital or poor infrastructure.

In developing countries, there exist a small number of

privately funded centralized testing centers that have essen-

tially the same infrastructure and resources as the testing

centers in Western countries (Table 2). By contrast, in most

centralized testing centers of developing countries, cost (due to

limited budgets via public financing) and availability of skilled

workers (due to attrition of the best workers) are still limited

compared to the centers of Western countries. Thus, the cost

of the microfluidic device (which includes both the material

and the manufacturing process) must be kept low in most

settings in developing countries. Moreover, for remote point-

of-care testing in developing countries, the fixed instrument

must be portable and cheap, and the disposable must be

a Disease categories as grouped by Murray and Lopez,8 except maternal, perinatal, and nutritional conditions are shown as a separatecategory. b The burden of disease as measured by the percentage contribution to total disability-adjusted life years (DALYs) in middle- andlow-income countries. Percentages were derived using data from WHO Global Burden of Disease 2002 revised estimates by World Bank incomegroups (high, upper middle, lower middle, and low income countries)9 http://www3.who.int/whosis/menu.cfm?path=whosis,burden,burden_estimates,burden_estimates_2002N,burden_estimates_2002N_2002Rev&language=english c Data takenfrom ref. 5, 7–9, 18. Abbreviations used: immunochromatographic (IC), immunoassay (IA), enzyme-linked immunosorbent assay (ELISA),microscopy (mic.), venereal disease research laboratory (VDRL), rapid plasma regin (RPR), fluorescent treponemal antibody-adsorption (FTA-ABS), T. pallidum hemagglutination assay (TPHA), agglutination (agg.), culture (cul.), iodine (iod.), vitamin (vit.), gram stain (GS),cerebrospinal (CSF), hypertension (hypertens.), iron (Fe), infections (infect.), Down syndrome (DS), disorder (dis.), ischaemic cerebrovasculardisease (isc.), rheumatory heart disease (rheum.), inflammatory heart disease (inflamm.), depression (deprs.), hepatitis B surface antigen(HBsAg), antibody to hepatitis B surface antigen (anti-HBs), antibody to hepatitis B core antigen (anti-HBc), alpha-fetoprotein (AFP),hepatitis C virus (HCV), C- reactive protein (CRP), prostate-specific antigen (PSA), brain naturietic peptide (BNP), hypertensive heart disease(hyp.)., nephritis and nephrosis (neph.), benign prostatic hypertrophy (bphyp.), low weight (LW.), birth asphyxia (BA), hemorrhage (hem.),sepsis (seps.), conditions (cond.), road accidents (RA), drownings (dr.), self-inflected injuries (SII), white blood cell (WBC), Sx/Hx/PE(symptoms/medical history/physical exam), red blood cell (RBC).

Table 1 Important diseases in developing countries, burden of disease, diagnostic assays, and corresponding potential LOC devices (Continued )

44 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

Tab

le2

LO

Cd

esig

nco

nst

rain

tsin

dif

fere

nt

sett

ing

sa

Co

nst

rain

to

nd

esig

ncr

iter

ia

Hig

h-

inco

me

cou

ntr

ies

na

tio

na

lte

stin

gce

nte

rb

Lo

w-

&m

idd

le-

inco

me

cou

ntr

ies

cen

tra

lize

dla

b(p

riva

te)c

Mil

ita

ry

Ex

tra

-te

rres

tria

lse

nso

rs

Hig

h-

inco

me

cou

ntr

ies

po

int-

of-

care

(PO

C)

Lo

w-

&m

idd

le-

inco

me

cou

ntr

ies

na

tio

na

l/re

gio

na

lte

stin

gce

nte

rd

Lo

w-

&m

idd

le-

inco

me

cou

ntr

ies

rura

lh

ealt

hcl

inic

e

Lo

w-

&m

idd

le-

inco

me

cou

ntr

ies

rem

ote

PO

Cf

Ab

sen

ceo

fgro

un

del

ectr

icit

yU

UI

IU

US

IL

ow

cost

of

fixed

inst

rum

ent

UU

UU

US

II

Lo

wco

sto

fd

isp

osa

ble

sU

UU

US

II

IA

bse

nce

of

tra

ined

end

-use

rsU

US

N/A

IS

SI

Ab

sen

ceo

feq

uip

ped

end

-use

faci

liti

esU

UI

II

SI

I

Ra

pid

An

aly

sis

UU

IS

IU

II

Hig

hse

nsi

tiv

ity

&sp

ecif

icit

yI

II

II

II

IL

arg

efl

uct

ua

tio

ns

inte

mp

era

ture

US

II

IS

II

Po

rta

bil

ity

UU

II

IS

II

Ro

ug

hh

an

dli

ng

US

II

SS

II

aI

=im

po

rta

nt,

S=

som

ewh

at

imp

ort

an

t,U

=u

nim

po

rta

nt.

bIn

aty

pic

al

in-h

ou

seh

osp

ita

lla

bo

rato

ryin

Wes

tern

cou

ntr

ies,

for

exam

ple

,co

sts

of

rea

gen

tsa

re$

5fo

rim

mu

no

ass

ay

s,a

nd

$5

–$

30

for

nu

clei

ca

cid

test

s.138

Rei

mb

urs

emen

tra

tes

are

typ

ica

lly

$2

0–$

50

per

test

for

imm

un

oa

ssay

s,a

nd

$5

0–

$3

00

for

nu

clei

ca

cid

test

s.F

ixed

inst

rum

ents

(su

cha

sli

qu

idh

an

dli

ng

rob

ots

an

dd

etec

tors

)ca

nco

sth

un

dre

ds

of

tho

usa

nd

so

fd

oll

ars

,a

lth

ou

gh

they

can

be

lea

sed

or

bo

rro

wed

usi

ng

rea

gen

t-re

nta

la

gre

emen

ts.

Typ

ica

lly

,tu

rna

rou

nd

tim

esfo

rm

ost

test

so

fb

etw

een

0.5

an

d2

da

ys

(fro

mth

eti

me

itis

ord

ered

toth

eti

me

the

resu

ltis

pro

vid

edto

the

ph

ysi

cia

n).

Excl

ud

ing

sam

ple

tra

nsp

ort

ati

on

toth

ela

b,

turn

aro

un

dti

me

for

emer

gen

cyte

stin

gis

ab

ou

t1

h.

Mo

stre

ag

ents

are

sto

red

inth

efr

idge

un

til

tim

eo

fu

se.

cT

his

hea

din

gd

escr

ibes

cen

trali

zed

test

ing

cen

ters

that

are

fun

ded

by

pri

vate

org

an

izati

on

s(e

.g.

ph

ila

nth

rop

ies,

NG

O).

Th

ese

test

ing

cen

ters

are

typ

ica

lly

loca

ted

inu

rba

nlo

cati

on

s,a

nd

can

be

as

wel

l-eq

uip

ped

as

test

ing

cen

ters

inW

este

rnco

un

trie

s.A

nex

am

ple

isth

eM

TC

T-P

lus

Init

iati

ve

tha

tfu

nd

edtw

ocl

inic

al

lab

ora

tori

esin

Ma

pu

toa

nd

Na

mp

ula

top

rov

ide

dia

gn

ost

ics

serv

ices

for

sup

po

rtin

gH

IVp

rog

ram

sin

Mo

zam

biq

ue.

dC

entr

ali

zed

test

ing

cen

ters

inn

ati

on

al

or

reg

ion

al

hea

lth

cen

ters

are

typ

ica

lly

fun

ded

by

the

go

ver

nm

ent,

an

da

rere

spo

nsi

ble

for

ma

ny

of

the

test

sin

the

cou

ntr

y.

Th

eq

ua

lity

of

thes

eh

ealt

hce

nte

rsv

ary

sub

sta

nti

all

y,

dep

end

ing

on

the

inv

estm

ent

of

the

go

ver

nm

ent

into

pu

bli

ch

ealt

hin

frast

ruct

ure

.4F

or

exam

ple

,a

cell

-co

un

tin

gin

stru

men

t(a

bo

ut

$2

00

00

)w

ou

ldb

ea

mo

ng

the

mo

stex

pen

sive

inst

rum

ents

,w

ith

typ

ica

leq

uip

men

tin

clu

din

ga

spec

tro

ph

oto

met

er,

am

icro

sco

pe

an

da

cen

trif

uge

cost

ing

$1

000

to$

20

00

each

.e

Ru

ral

tow

ns

oft

enh

av

ea

loca

lh

ealt

hcl

inic

or

ah

osp

ita

l,w

ith

aw

ide

ran

ge

of

con

dit

ion

s.O

ften

,th

eir

clin

ica

lla

bo

rato

ries

are

run

by

po

orl

ytr

ain

edw

ork

ers,

are

po

orl

yeq

uip

ped

,a

nd

ha

ve

inte

rmit

ten

to

rn

og

rou

nd

elec

tric

ity

.O

ne

such

lab

ora

tory

wo

uld

be

equ

ipp

ed,

for

inst

an

cew

ith

ace

ntr

ifu

ge

(ma

nu

al

or

elec

tric

),a

mic

rosc

op

e(f

or

cou

nts

of

cell

sli

ke

pla

tele

tso

rto

tal

WB

C,

the

dia

gn

osi

so

fT

Bu

sin

gco

lora

tio

ns

an

dth

ed

irec

to

bse

rva

tio

no

fst

oo

l),

sem

i-q

ua

nti

tati

ve

stri

pte

sts

for

clin

ica

lch

emis

try

ap

pli

cati

on

s(i

.e.,

pH

an

dsu

ga

rin

uri

nes

),a

gg

luti

na

tio

nte

sts

for

HIV

,a

nd

the

rea

gen

tsfo

rb

asi

cte

sts

lik

eb

loo

dty

pe

com

pa

tib

ilit

yo

ng

lass

slid

es.

fT

hes

ete

sts

can

be

ad

min

iste

red

an

yw

her

ein

dev

elo

pin

gco

un

trie

s.C

urr

entl

yu

sed

no

n-L

OC

test

sin

this

cate

go

ryin

clu

de

yes

/no

imm

un

och

rom

ato

gra

ph

icte

sts

for

ma

lari

a(i

.e.,

aP

ara

chec

kP

f,w

hic

ha

ta

pri

ceo

f$

1ca

nb

eli

mit

edto

an

emer

gen

cyca

sefo

rru

lin

go

ut

infe

ctio

no

fP

lasm

odiu

mfa

lcip

aru

m)

or

sem

i-q

ua

nti

tati

ve

stri

pte

sts

for

clin

ica

lch

emis

try

.A

nex

tern

al

inst

rum

ent

mu

stb

eli

gh

t,p

ort

ab

le,

rugg

ed,

an

dch

eap

(ten

so

fd

oll

ars

or

chea

per

,fo

rw

ides

pre

ad

use

),w

ith

ver

ych

eap

dis

po

sab

lem

icro

flu

idic

chip

s(p

enn

ies)

.F

or

exam

ple

,o

pti

cal

mic

rosc

op

esin

such

sett

ings

can

be

on

lyeq

uip

ped

wit

ha

mir

ror

as

ali

gh

tso

urc

eto

faci

lita

tem

ain

ten

an

ce.

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 45

extremely cheap. All components of the device (including

the instrument and disposable) must be robust and rugged

under a variety of environmental conditions. Overall, remote

point-of-care testing in developing countries imposes perhaps

the severest constraints on the design of LOC devices, with

extremely low cost a distinguishing feature from most

applications in the Western world.

Although interest in designing LOC devices for developing

countries is only beginning, it will be beneficial to exploit the

commonalities in the settings of developing countries with

other resource-poor settings in Western countries (Table 2).

For example, one can leverage the large body of existing

research on LOC designs for point-of-care testing for

physicians’ and home use,20,21 devices for military applica-

tions22 and first responders, and extraterrestrial sensors23–25 in

designing LOC devices for developing countries (Fig. 1). In all

these settings, integration, portability, low power consump-

tion, automation, and ruggedness are important qualities.

These general design constraints suggest some LOC com-

ponents and procedures to be more appropriate than others

in resource-poor settings. In Fig. 2, we outline a sample of

appropriate LOC technologies for use in developing countries.

In general, the differences in appropriate LOC technologies are

pronounced between centralized testing versus point of care,

with cost being the distinguishing feature between technologies

for use in high-income versus low-income countries.

Material and manufacturing

To minimize the cost of the microfluidic device, it is important

to reduce the footprint of expensive components such as glass

($500–4000 m22),26 quartz, and silicon (a number of challen-

ging issues exist in the scale-up of silicon micromachining for

biological devices27). An alternative is to use plastics, which

are inexpensive (the manufacturing cost of an injection-

moulded device is generally less than $0.3028), available in an

abundant choice of materials, and appropriate for single-use

disposal to avoid cross-contamination. Challenges in plastic

include minimization of batch-to-batch variation, improve-

ment in chemical resistance, improvement in control over

surface chemistry, and compatibility with fluorescence.26,29,30

Additional steps for processing the microfluidic chip (such as

Fig. 1 Pictures of current LOC devices for use in remote settings. (A) A handheld device, iSTAT, for measuring electrolyte levels. Taken from

www.istat.com with permission of i-STAT Corporation. (B) A portable device and a fixed instrument for analyzing DNA from the company

Cepheid. Taken from www.cepheid.com with permission of Cepheid Inc. (C) Mars Organic Analyzer, an extraterrestrial LOC device. Reprinted

from ref. 24. Copyright 2005 by the National Academy of Sciences of the United States of America, all rights reserved.

Fig. 2 A range of appropriate LOC procedures for different settings.

46 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

pre-treatment of surfaces with capture reagents) should be

simple and scalable to minimize the cost of the manufacturing

process.

Storage and transportation

Unlike controlled research environments, the LOC device

will be subjected to a variety of environmental conditions.

Reagents, including those stored inside the microfluidic chip,

must be stable to fluctuations in temperature as well as

physical shocks. Methods for stabilizing dry reagents (such as

trehalose,31 a chemical that has been used to stabilizing dried

proteins in conventional 96 well ELISA assays) and wet

reagents32,33 will be needed.

Sample pre-treatment

A number of sources of physiological fluids are available.

Although whole blood (from venipuncture or finger prick)

and its derivatives (plasma and serum) are most common,

the use of non-invasive samples such as saliva34 and urine35 are

gaining prominence. For real-world samples, sample pre-

treatment before the analysis step is needed. Pre-treatment

steps include sampling, extraction, filtration, pre-concentra-

tion, and dilution;36 a centrifugation or filtration step is

necessary, for example, to obtain plasma or serum from whole

blood. In a centralized laboratory, these steps can be

performed by a technician or a liquid handling robot before

injection into the microfluidic chip. In remote settings,

however, automation and integration of these steps in the

LOC device is ideal.37–43 To minimize cost and power

consumption, passive methods may be most appropriate.

Fluid actuation

An ideal LOC device for developing countries should be

capable of actuating the flow of fluids with reliable flow rates

using inexpensive and compact instrumentation. Electrokinetic

actuation of fluids is popular in research laboratories, but it

requires a charged surface for electroosmotic flow (which

limits the type of material that can be used) and a high voltage

supply. Pneumatic actuation may be most practical for

portable applications, with battery- or hand-powered vacuum

sources.44 Capillary force is a simple method for pumping

fluids in portable LOC devices.45

Fluid control

For complex assays, a series of different reagents need to be

delivered into the microfluidic chip. In centralized testing

facilities, these procedures can be performed manually by a

technician, an external liquid handling robot, or on-chip valves

that are controlled by an external instrument. For portable

automated devices, passive delivery of a series of reagents is an

attractive option.32,45–47

Mixing

Some assays will require mixing of samples with different

reagents. In such cases, active micromixers can be used if a

power supply is available.48 Passive mixers, which rely on the

geometry and topography of the microchannels, can also be

used to mix and dilute samples.49 In general, however,

heterogeneous assays (which include many immunoassays)

do not require mixing since the analyte is captured on the

surface.

Signal detection

An intrinsic challenge in microfluidics is detection of a signal

emanating from a small physical region; in developing

countries, this detection must be inexpensive, and ideally, use

compact instrumentation that consumes little power.

Fluorescence is a sensitive and popular detection method,

but typically requires expensive and complicated optics and

consumes significant power, whereas absorbance can be low-

cost.44,50 With simple electronic modulation, the background

in optical detection can be shielded from ambient light.44

Electrical measurements such as conductance are also poten-

tially appropriate low-cost and portable detection methods for

use in developing countries.51

Disposal

In point-of-care settings in both Western and developing

countries, it is ideal to contain the chemical reagents and

blood samples in the LOC device for disposal. Also, because

incineration is often not accessible, environmentally friendly

chemicals are preferred.

Overall strategy for development of LOC devices

More broadly, in developing a LOC device for a new setting,

scientists and engineers can take two different approaches:

adapt existing methods or design new technologies. Both

approaches have been undertaken in the past for developing

countries. Adaptation of Western-world technologies for use

in developing countries has a number of precedents in

technology-transfer projects; to be successful, these projects

must carefully take into account the local needs, culture, and

constraints.52 It is arguably more challenging (but perhaps

more scientifically rewarding) to develop new technologies

with consideration of local factors from the earliest stages of

design. Collaboration with local partners could produce a

device that best suits the health needs of the local people

(rather than a device driven by the convenience of available

technology); with the right initial testing group, this route can

succeed extremely well as a disruptive technology.53

4. Review of current work on LOC devices for globalhealth

4.1 Overview

Examination of diagnostic tests that are currently used in the

field in developing countries can bring insights for designing

LOC devices. Most of the current diagnostic tests used in

developing countries are simple to use and provide rapid

results.54 The most prevalent example is immunochromato-

graphic tests (also known as dipstick or lateral-flow tests),

which provide yes/no results in minutes in the form of a visible

band (these tests typically use gold colloids or latex beads

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 47

conjugated to antibodies).55–57 Moreover, immunochromato-

graphic strips are cheap to produce. These strip tests, however,

are not quantitative, and are not sufficiently sensitive for the

detection of all important markers. As such, development of

strip tests for diseases in developing countries (such as

chlamydia and trachoma from Lee’s group)58 is ongoing.

LOC devices bring exciting capabilities of high analytical

performance, but they must be made cost-effective, among

other important requirements (Table 2). Also, LOC devices

can also potentially be used for multiplexed and parallel

analysis of many relevant markers at once; this capability,

however, is challenging since different analytes typically call

for the designs of different LOC methods. Below, we review

LOC studies that have been applied (or have the potential to

be applied) for use in developing countries, as grouped by the

class of analytes.

4.2 Proteins

A wide range of diseases is characterized by changes in protein

concentrations in a patient’s physiological fluids. These

diseases span viral infections (e.g. anti-HIV antibodies as a

marker for HIV/AIDS), bacterial infections (e.g. enterotoxin B

as a marker for Staphylococcus aureus), parasitic infections

(e.g. histidine-rich protein 2 as a marker for malaria), and

non-communicable diseases (e.g. PSA as a marker for prostate

cancer) (Table 1). Immunoassays are routinely used, with

high sensitivity and specificity, to detect and quantitate

protein markers. The most commonly used samples from

the patient are whole blood, serum, and plasma, with less

common samples being saliva, urine, feces, sperm, tears and

sweat. In developing countries, the use of fluids that can be

sampled non-invasively can encourage adoption of tests and

decrease the incidence of infection due to contaminated

needles. For example, saliva and urine offer a simple and safe

alternative to blood sampling, but they typically contain

lower concentrations of protein makers than in blood;

successful detection will necessitate an improved sensitivity in

the LOC device. As an example, a LOC immunoassay

developed by McDevitt and colleagues to measure levels of

C-reactive protein in saliva required a 1000-fold improvement

in sensitivity over ELISA in microtiter plates (by using porous

beads to increase the surface density of capture probe on the

solid phase).59 Microfluidic chips to detect enteric antigens

from human stool, a complex sample matrix, are being

developed.60

Enzyme immunoassays, which comprise most protein tests,

typically require the established infrastructure of centralized

testing facilities to accomplish complex reagent handling and

optical detection. LOC devices have the potential to transpose

antigen–antibody assays into assay formats that are much less

demanding in infrastructure. At least two important hurdles

exist in the processes of miniaturization and automation:

storage of multiple reagents and fluid handling capability to

carry out the complex protein assay, and detection of the

signal in the microfluidic system. Below, we review approaches

that have addressed these challenges using inexpensive and

portable solutions that are, or have the potential to be,

compatible with use in resource-poor settings.

(1) Fluid actuation. Capillary force is a simple method for

pumping fluids in a LOC device, because the liquid flows

spontaneously with no external power or moving parts.

Delamarche and co-workers demonstrated autonomous

capillary flow in an array of microchannels to carry out an

immunoassay for C-reactive protein.45 The sensitivity was

increased by integrating Pelletier elements underneath the

LOC device to tune the rate of evaporation and hence capillary

flow.47 As an alternative to capillary force, pressure or vacuum

can be generated by applying a finger on the surface of a LOC

device, as illustrated by an assay for botulinum toxin

developed by Beebe and co-workers,33 or the commercially

available ABO Card from the company Micronics. A hand-

operated vacuum pump can also be used to actuate fluid flow

in the field.32,44

(2) Mixing and fluid control. Besides pumping, fluid mixing

is often required in protein assays. In resource poor-setting,

passive mixers offer the advantages of intrinsic automation

(no user intervention) and the absence of power requirements.

Planar mixers based on chaotic mixing with staggered

herringbones,61 creation of bubbles,62 in situ photopoly-

merized porous material,42 three-dimensional microchannels,41

design of curved channel geometries,63 and other methods48

have demonstrated efficient mixing capabilities. Whitesides

and colleagues created a device based on splitting and re-

mixing to dilute a sample over a range of 210 (or y1000-fold),

thus circumventing off-chip pipetting steps.49 Also,

Delamarche and colleagues developed a micromosaic immuno-

assay that significantly reduced the number of pipetting steps

required for a multiplexed assay;64 this method was used to

develop a panel test for cardiac markers (C-reactive protein,

myoglobin, and cardiac troponin I).65

We and Whitesides reported a simple and reliable technique

for storing and delivering a sequence of reagents to a

microfluidic device to carry out automated immunoassays32

(Fig. 3A). In this method, cartridges made of commercially

available tubing were filled by sequentially injecting plugs

of reagents separated by air spacers (which prevented the

reagents from mixing with each other); in this form, the

reagents were stable to shocks, and antibody solutions could

be stored for months without loss in activity. By applying

negative pressure at the outlet, all reagents were dispensed

sequentially, and a solid-phase immunoassay could be

completed in 2 minutes with low nM sensitivity. Another

attractive method for passive fluid control and delivery is

the autonomous capillary system,45,47 although this

method currently requires a multi-step fabrication process.

In contrast to passive delivery, active valves can also be

used to deliver a complex series of pre-stored reagents.

The groups of Beebe33 and Whitesides66 have developed

inexpensive, hand-operated valving systems for point-of-care

immunoassays. For long-term storage at high temperatures,

storage of the reagents in a dry form may be more stable than

as wet liquids. Yager and colleagues demonstrated that

enzymes could be stored dry in LOC devices in mixtures of

dextran and trehalose.67

All common fluid handling steps required for protein assays,

including actuation and control of fluid flow, have been

48 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

demonstrated on centrifugal microfluidic devices.68,69 For

example, the Bioaffy chip from the company Gyros can

quantify clinical markers such as a-fetoprotein, interleukin-6

and carcinoembryonic antigen down to low pM concentra-

tions.70 Also, Bernard and colleagues used a common

compact-disc player as a digital detector of silver-based signals

of C-reactive protein in immunoassays;71 the simplicity of this

overall format makes it attractive for use in resource-poor

settings.72

(3) Signal detection. Silver dots produced by autometallo-

graphic precipitation are also directly detectable by optical

density measurements, as illustrated by the microfluidic

POCKET assay as developed by ourselves and Whitesides

and co-workers,44 as well as by Mirkin and colleagues using a

scanometric reader.50 Since amplification resulted in a signal

that was immobilized on a surface, the POCKET assay

avoided washing away optically active and freely diffusible

products that would be generated in a continuous-flow format

for ELISA (Fig. 3A). Importantly for use in developing

countries, since the silver signal developed over an area of

2 6 2 mm2, an inexpensive custom-built detector (for less than

$45 in components, including a laser diode and a photo-

detector) can be used to detect the signal, thereby circumvent-

ing the need for expensive optical instrumentation for

detecting signals confined to small microchannels.

For high-sensitivity assays, Mirkin and co-workers have

reported an assay based on DNA-coated nanoparticles,

magnetic separation, and PCR to detect protein markers at

up to 6 orders of magnitude in improvement in the limit of

detection compared to conventional assays.73 This format

can in principle be adapted to a low-cost LOC device. High-

sensitivity and quantitative assays can greatly benefit certain

applications, including the measurement of levels of HIV-1

p24, a viral protein antigen which has been advocated as a

potential simpler alternative to viral load or CD4 counting for

Fig. 3 Simple and low-cost LOC methods for detecting proteins in developing countries. (A) Optical detection of proteins and reagent storage and

delivery. (i) Schematic representation of the POCKET immunoassay powered by a 9 V battery. (ii) Actual device. (iii) Apparent silver absorbance

values of anti-HIV-1 antibodies from HIV-positive patients and control patients. (iv) Schematic representation of reagent-loaded cartridges. (v)

Overlay of fluorescence and brightfield images of the immunoreaction area, with fluorescent signal corresponding to presence of labeled detection

antibodies on antigen stripes. The concentrations indicated above the picture refer to the concentration of sample tested in each microchannel.

Reprinted from ref. 32 with permission from ACS Publications. (B) Immunomagnetic separation and detection of proteins with CMOS Hall

sensors. (i) Schematic representation with inset showing actual chip. (ii) Comparison of the outputs of CMOS chip and ELISA. Reprinted from

ref. 78 with permission from Elsevier.

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 49

monitoring AIDS progression in HIV patients and diagnosing

HIV/AIDS in newborns.74

With appropriate amplification schemes, surface plasmon

resonance (SPR), which detects at the surface minute changes

in the index of refraction induced by the binding of molecule,

can approach the sensitivity of ELISA.75 The company Texas

Instruments Sensors & Controls (now renamed Sensata

Technologies) has developed a portable SPR sensor (named

Spreeta) for heterogeneous antibody-antigen binding and

solid-phase DNA hybridization; this disposable device is

designed to be manufacturable in very large quantities.76 The

device can be integrated with a temperature-controlled

instrument that runs on a 12 V battery to detect enterotoxin

B in urine, milk, and sea water, with a sensitivity in the fM

range.77 Currently, a Spreeta evaluation module is available

at $200 per sensor (http://aigproducts.com/surface_plasmon_

resonance/spr_evaluation_module.htm). Since the gold-coated

chip could be regenerated up to 80 times before disposal, each

assay can potentially be priced below $1 in the future.77

Boser, Harris, and colleagues developed on a 2.5 6 2.5 mm2

CMOS chip an array of Hall sensors to quantify the number of

magnetic beads associated to immunocomplexes at the surface

of the sensor (Fig. 3B).78 The use of magnetic beads facilitated

removal of unbound antibodies conjugated to magnetic beads,

and produced signals at the surface that were recorded by the

Hall sensors. The average reading from 120 sensors was

sufficient to quantify dengue fever antibodies in clinical serum

samples with a good correlation compared to ELISA assays.

When combined with proper fluidic control, this method can

potentially be developed into an integrated simple and low-

cost LOC device for immunoassays.

4.3 Nucleic acids

Analysis of nucleic acids offers powerful diagnostic informa-

tion that complement protein analysis of antigens and

antibodies. For example, by analyzing conserved DNA or

viral RNA sequences, PCR and RT-PCR can be used to

specifically detect infectious diseases important in developing

countries (such as HIV/AIDS, hepatitis B and C, and TB).79,80

For HIV/AIDS, quantitative measurements of RNA levels

(based on amplification of the 59-long terminal repeat) provide

information on the stage of diseases; as such, low-cost methods

for PCR have been studied for use in developing countries.81–83

As a technology, nucleic acid detection can be very sensitive

due to amplification, and specific due to the intrinsic com-

plementarity of the base-pairing interactions. Nevertheless, the

building of an integrated LOC device for detecting nucleic

acids is typically more challenging than for proteins. Overall,

there are at least three LOC design issues for nucleic acid

detection.

(1) Sample pre-treatment. A general challenge in nucleic acid

detection is the requirement of processes (such as cell sorting,

concentration, and lysis, as well as DNA extraction) to isolate

the DNA or RNA of interest from desired cells,84–86 in

contrast to protein detection in which the analyte is typically

free-floating in the blood, saliva, or urine sample. These steps

of sample pre-treatment can take place off the chip, but for use

in remote settings with untrained users, it is ideal to integrate

these steps seamlessly with the rest of the microfluidic

processing steps.87 The challenge in developing countries is

even greater since these procedures must be performed at

low cost.

Fig. 4 LOC methods for detecting nucleic acids that can be adapted for use in developing countries. (A) Integrated nanolitre DNA analysis

device. (i) Schematic representation with two liquid samples and electrophoresis gel present. (ii) Optical micrograph of device. Reprinted with

permission from ref. 90. Copyright 1998 AAAS. (B) Schematic representation of oligonucleotide-conjugated nanoparticles for probing DNA

sequence arrays. Reprinted with permission from ref. 50. Copyright 2000 AAAS.

50 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

A number of groups have successfully integrated sample

pre-treatment with analysis.84,87 For example, Quake’s group

used valves to automate cell isolation, cell lysis, nucleic acid

purification, and analysis on the same microchip.86 Integration

of sample pre-treatment with analysis is important to achieve

ease of use, as well as to improve sensitivity by reducing

sample losses in between steps. For example, integration of

cell capture, cell lysis, mRNA purification, cDNA synthesis,

and cDNA purification has been demonstrated for a RT-PCR

microfluidic chip.88 Grodzinski and co-workers have

developed a self-contained device in plastic that integrates

sample preparation, cell capture, cell preconcentration

and purification, cell lysis, PCR, DNA hybridization, and

electrochemical detection to analyze DNA from pathogenic

bacteria.89 In addition, metering samples is important to

automate sample preparation,90 an important consideration in

remote settings.

(2) Method of signal amplification. PCR/RT-PCR.

Miniaturizing PCR on LOC devices has the potential to

reduce the cost of reagents, speed up analysis, and automate

the procedure for use in remote settings by integrating multiple

functionalities such as cell concentration and lysis, DNA

extraction, removal of PCR inhibitors, amplification of DNA,

and separation and detection of the amplified products of

interest.84 In the most straightforward adaptation of conven-

tional PCR into LOC devices, a microchamber or microwell

can be created in which the sample and PCR reaction mixture

are thermally cycled (Fig. 4A). In one of the first studies by

Burns and colleagues (which featured microfluidic channels,

mixers, heaters, temperature sensors, and fluorescence detec-

tors90), the low voltages and power suggested that hand-held

battery operation is feasible; this technology is now being

commercialized by the company HandyLab. Although

directed more for biodefense than global health, the company

Cepheid has developed a miniature analytical thermal cycling

instrument (MATCI) that consists of silicon-micromachined

reaction chambers with integrated heaters, optical windows,

and diode-based fluorescence detection.22,91 Although the

current size of these instruments may be too large for use in

remote testing, they may be appropriate for centralized testing

centers in developing countries. Similarly, since most LOC

devices that use well-based PCR require bulky instruments as

well as expensive and complex manufacturing, they may be

most appropriate for use in centralized testing centers.92–94 The

design of disposable micro-PCR devices on polycarbonate

plastic95 may ultimately be suitable for use in resource-poor

settings, although it currently lacks extensive integration.

In contrast to well-based LOC PCR, continuous-flow

PCR systems operate by passing a sample continuously over

regions of different temperatures. Continuous-flow systems

offer flexible design geometry (for changing the number of

amplification cycles), and fast transition times for heating and

cooling (which depend on the flow rate and kinetics for

reaching thermal equilibrium).84,96 Another design that is

potentially simple to manufacture and simple to use include

passive reactors in closed-loop designs that operate without

valves.97 An interesting novel scheme for PCR amplification

takes advantage of convective flow inside a Rayleigh–Benard

cavity to yield comparable performance to conventional

PCR;98 because this system requires only a single heating

element held at a fixed temperature, it can potentially be made

low cost, although design challenges exist in adapting the

system to a LOC device.84

Isothermal. The need for temperature cycling in PCR has

made it challenging to build low-cost and simple devices

suitable for point-of-care testing. An exciting development that

bypasses thermocycling is isothermal DNA amplification,

which includes techniques such as single-strand displacement

amplification, rolling circle amplification, and ligase chain

reaction.84 Harrison and co-workers have integrated isother-

mal amplification in an electrokinetic LOC device that used

cycling probe technology to amplify a DNA sequence from

S. aureus.99 More recently, Zhang and co-workers demon-

strated loop-mediated isothermal amplification (LAMP) in a

cross-shaped microfluidic system in PMMA.100 Also,

Gulliksen and colleagues used an isothermal amplification

method in a microfluidic device made of cyclic olefin

copolymer for multiplexed detection of human papilloma

virus at-the-point-of-care application.101 In the future, other

schemes (such as helicase-dependent DNA amplification102)

may be integrated into LOC devices.

(3) Detection. The most popular method for analyzing DNA

after amplification is gel electrophoresis of fluorescently

labeled DNA. In LOC devices, DNA analysis by capillary

electrophoresis may be suitable for centralized testing centers

in which power supplies and external fluorescence detectors

are available. For remote testing, molecular beacons, which

are single-stranded oligonucleotides whose fluorescence is

dequenched upon hybridization to a target probe, are a

promising technology for use in developing countries due to

their high sensitivity and specificity.103,104 For example, they

have been used to detect pathogenic retroviruses,79 and in

LOC devices to screen for the breast cancer gene

(BRCA1).105,106 The use of molecular beacons, however, still

requires an external fluorescence detector.

A potentially low-cost and sensitive detection system for

nucleic acids that may be appropriate for resource-poor

settings is oligonucleotide-conjugated nanoparticle probes, as

demonstrated by Mirkin and others (and now commercialized

by the company Nanosphere) (Fig. 4B). Coupled with silver

reduction amplification, they can be quantitated by an

inexpensive scanometric reader,50 and potentially by a low-

cost and portable reader.44 These nanoparticles, when reduced

to form a micron-sized metallic bridge across an electrode gap,

can also result in quantifiable changes in conductivity,73 which

can in principle be measured by a low-cost and portable

conductivity meter. Other electrochemistry-based methods for

detecting DNA have been reported.107 Simple detection of

amplified nucleic acid products with a dipstick method for

resource-poor settings has been demonstrated.60,108

4.4 Cells

Analysis and counting of cells are important for diseases such

as anaemia and hematology (via erythrocyte and complete

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 51

blood counts), as well as for monitoring the progression of

AIDS. Flow cytometry, the current standard for cell analysis

and counting, can measure up to 10 or more cell properties

and separate and isolate cells at rates up to 10 000 cells per

second without loss of viability.109 Since conventional flow

cytometers are bulky, expensive, and mechanically complex,

they are currently limited to well-financed centralized testing

centers.

Due mainly to the importance of counting CD4+ lympho-

cytes for monitoring the progression of AIDS, a number of

initiatives have started to support the development of an

inexpensive and compact device for cell counting for global

health. In one non-LOC method, Mwaba and colleagues used

filter papers to store dried blood samples, which were

transported to a centralized facility for ELISA testing using

anti-CD4 antibodies.110 The results of this simple technology

were encouraging but exhibited limitations in accuracy. With

support from the Gates Foundation, Imperial College London

is supporting the development of a simple, low-cost, and semi-

quantitative CD4+ lymphocyte-counting device (http://

www1.imperial.ac.uk/medicine/about/divisions/medicine/infec-

tious_diseases/cd4_initiative/) that exhibits cut-offs at 200, 350,

500 cells mm23 with 10% coefficient of variation. Perhaps

more so than simple membrane-based tests, LOC devices have

the potential to meet these targets due to their increased

versatility in design and enhanced analytical performance.

Fluid control for design of mechanism of cell sorting. There

are different methods for designing a LOC device for cell

counting, all of which require different methods for fluid

control. For example, conventional flow cytometers use a

sheath fluid to enclose a stream of cells such that the cells pass

by the detector one by one in a single file for analysis. In a

LOC device, microfluidic mechanisms such as hydrodynamic

flow switching, electrokinetic flow switching, dielectro-

phoresis, and electrowetting-assisted flow switching can be

used to focus the cells into a stream.109 Valves can

subsequently be used to sort the cells.111 These devices,

however, have yet to be made portable and inexpensive.

A different approach to count cells takes advantage of the

relatively large size of cells (compared to the scale of

microfabrication techniques) by capturing them for analysis.

For example, in an initial study based on the capture of

microbeads, McDevitt and colleagues micromachined arrays

of pyramidal cavities on silicon wafers; these cavities housed

microspheres that produced optical changes in the presence of

analytes.112 Subsequently, Rodriguez, Walker, and colleagues

adapted this device (by adding a polycarbonate, track-etch

filter that selectively trapped lymphocytes and not red blood

cells) to capture and measure the levels of CD4+ lymphocytes

from blood samples in Botswana (Fig. 5).113 The results were

in good agreement with those obtained with a conventional

flow cytometer. This device (now being commercialized by the

company LabNow) is potentially cheaper than other available

systems for single-purpose flow cytometry114 and microbead

separation; because of the cost, bulkiness, and power

requirements of an epifluorescence microscope and a camera,

however, the current system is likely most suitable for

centralized testing centers rather than remote point-of-care

testing. Other inexpensive flow cytometric methods have been

developed, including capabilities for multiplexing.115

A third approach for capturing and counting cells is

immunomagnetic separation, which typically uses antibody-

conjugated superparamagnetic beads to isolate the cells of

interest. Tibbe and co-workers used antibody-labeled ferro-

magnetic nanoparticles to perform a differential white blood

cell count (with analysis of neutrophils, lymphocytes, mono-

cytes, and eosinophils).116 In a magnetic field, immuno-

magnetic cells are aligned in a capillary along the magnetic

field lines for fluorescent analysis. This design functions with

potentially simple fluidic control, but still requires a conven-

tional fluorescence imaging system.

Cell counting has important applications beyond the

monitoring of HIV/AIDS progression. For example,

Fig. 5 A low-cost LOC device for counting CD4+ lymphocytes. (A) Schematic representation of pyramidal wells in Si. (B) Scanning electron

micrograph of single well with microbead. Reprinted from ref. 112 with permission from ACS publications. (C) Schematic representation of the

device system. (D) (Left) Transmission image of membrane flow cell showing selective capture of lymphocytes. Holes are 3 mm in diameter. (Right)

Fluorescent antibody staining of lymphocytes. (E) Results of cell counting from microchip versus flow cytometry. Reprinted from ref. 113.

52 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

McDevitt and colleagues adapted their microbead system to

build a multifunctional LOC device for performing leukocyte

counts and measuring C-reactive protein levels, two important

indicators of coronary heart disease.117 Like the CD4+-

lymphocyte counting device, this device may be useful in

centralized testing centers in developing countries (in this case,

to address the increasing incidences of cardiovascular disease,

which constitutes 9.5% of total DALYs in developing

countries). In a different application, Chiu and colleagues

used a microfluidic device to show decreased deformability in

erythrocytes when infected with P. falciparum.118 Although

this study did not focus on a diagnostic application, it suggests

a potential route for diagnosing and monitoring malaria

infection using a LOC device. For example, in a study by

Gascoyne and colleagues in Thailand using dielectrophoresis

and field-flow fractionation, parasitized erythrocytes eluted

more quickly than normal erythrocytes.119

Another promising cell-based application of LOC devices

for global health is the miniaturization of microbiological

culture assays. Currently, conventional microbiological

techniques are used to identify drug-resistant bacterial strains;

this identification is critical for administering efficacious

therapy for TB patients. Techniques in culturing bacteria

in microfluidic chips120–122 can potentially automate this

laborious process (and other microbiological assays involving

differential cultures) even in remote settings. Devices that

culture and analyze pathogens and cells in microfluidic devices

could moreover be adapted to perform diagnostic procedures

that are conventionally microscope-based (such as blood

smears for diagnosis of malaria). Low-cost microscopy

using optofluidics, if it can be made robust, may be an

attractive technique in resource-poor settings.123 The power of

LOC technologies can potentially be augmented with genetic

and molecular biological approaches, such as Jacobs’ clever

luminometric technology for low-cost TB diagnosis using

luciferase-reporter phage124 (now commercialized by the

company Sequella).

4.5 Clinical chemistry

Currently, the most popular LOC technologies for analyzing

electrolytes are based on electrochemical detection. An active

area of research in this field is potentiometric sensing using

ion-selective field-effect transistors (ISFET); ISFETs, however

often require a large reference electrode.27 Nevertheless,

integration of electrochemical detection and semiconductor

technologies have resulted in commercial products, such as the

iSTAT from Abbott Diagnostics.20 This device is a portable

blood analyzer that uses microfabricated thin-film electrodes

to measure levels of electrolytes (Na+, K+, Cl2, Ca2+), general

chemistries (pH, urea, glucose), blood gases (pCO2, pO2),

and hematology (hematocrit). The electrochemical detection

system includes amperometry, voltammetry, and conductance,

depending on the analyte.

Despite this important achievement, there are limitations of

MEMS devices that feature electrochemical detection. The

lack of suitable manufacturing facilities makes it expensive

and, for some devices, impractical to scale up the manufactur-

ing of the sensor. Although it is in principle possible to

leverage existing microelectronics fabrication facilities for the

manufacturing of biological and chemical sensors, there exist a

number of challenging issues, such as differences in dimensions

(below 1 mm for microelectronics and above 5 mm for sensors),

in thickness and type of gate insulator, in materials (e.g. for

conductors, Al, polysilicon, and Cu for electronics, versus

Au and Pt in sensors), and in the passivation layer (e.g. high-

density silicon nitride for sensors that are exposed to

solutions).27,125,126 Although their current design still relied

on a bulky instrument for fluid actuation and detection,

Madou, Bachas and colleagues developed a LOC device that

measured electrolyte levels optically using optodes;127 in the

future, it may be possible to design a low-cost, integrated,

optical device for electrolyte measurements.128

4.6 Non-diagnostics applications of LOC devices in developing

countries

Although health diagnostics is the nearest-term application of

LOC devices in developing countries, other important areas of

global health can benefit in the future from this technology.

For example, LOC diagnostic devices can be used for

environmental sensing and monitoring.60 Sandia Labs, for

example, is developing a portable device to monitor water

quality by detecting pathogenic bacteria and toxins.129

Fig. 6 Integrated LOC devices with potential for use in developing countries. (A) Schematic representation of LOC for detecting enteric diseases.

Reprinted from ref. 60 with permission from the International Society for Optical Engineering. (B) Picture of a plastic LOC device for point-of-care

clinical diagnostics. Reprinted from ref. 139 with permission from the Proceedings of the IEEE.

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 53

In addition to diagnostics and sensors, LOC technologies

can be used to promote the development of therapeutic

compounds. The use of LOC technologies (through high-

throughput drug screening, genomics, and proteomics) for

drug discovery has been reviewed in detail elsewhere;130 as

research into drug discovery for neglected diseases increases

(in universities and industrial companies such as the Novartis

Institute for Tropical Diseases), LOC technologies can play

an increasingly important role. More broadly, Singer and

colleagues have investigated the potential contribution of

biotechnology, genomics, and nanotechnology to address

issues in global health and development;1,131,132 LOC techno-

logy has a clear potential to address these issues through its

close association with all these research fields.

Even when drugs (and vaccines) are available, simple

needle-free delivery into the patient is an important challenge

in developing countries.2 Current approaches for improving

drug delivery in developing countries include inhalation and

oral delivery, and are a focus of a non-profit organization

(Medicine in Need) based on the work of Edwards et al.133

Langer and colleagues have developed LOC devices for

programmed time-release of drugs.134,135 In the long term,

these technologies can conceivably be combined with other

miniaturized medical devices (such as wireless capsule endo-

scope) for use in health centers without large infrastructure.

5 Conclusion

There is a pressing need for new health technologies for

diagnosing and treating communicable and non-communic-

able diseases in developing countries. The LOC field is well-

positioned to contribute to this challenge by leveraging recent

advances in integrated devices for use in settings with low or

moderate resources (such as point-of-care health testing,

military sensors, and extraterrestrial devices), and through

advances in the young but growing field of LOC devices for

developing countries.

What will be the roadmap in the near future for designing

and deploying LOC devices in developing countries? First and

foremost, new devices will be needed (Fig. 6); the design

criteria of these devices are vast, demanding, and context-

dependent, and they will need to be considered carefully

from the early stages of development. Beyond the scientific

challenges, successful deployment of the device in developing

countries will involve a complex interplay of political and

socioeconomic considerations.136 Scientists will therefore need

to work closely with members from NGOs and local

governments as early as possible (and well before a field-

testable device is ready) to ensure proper distribution channels

(Table 4 and Table 5). Since much of the work in engineering

and development will best take place in the industrial rather

than academic setting, the private sector has a significant role

to play as well (Table 3). As an example of the importance of

such multidisciplinary efforts, the Bill and Melinda Gates

Foundation is supporting a consortium of academic

researchers (Yager and co-workers), industry (Micronics,

Nanogen, and Invetech), and an NGO (PATH) to develop a

multifunctional LOC device for infectious diseases137 (Fig. 6A),

and another consortium of academic researchers (Kelso and

co-workers) and industry (Abbott and Inverness Medical

Innovations) to develop a low-cost diagnostic device.

Finally, potential obstacles can be anticipated from studies

on the introduction and dissemination of LOC devices in

developed countries; these obstacles include cost per test

and reliability (see the market study FlowMap, available at

http://www.microfluidics-roadmap.com/).

Table 3 Sample list of current commercial ventures that have the potential to develop LOC devices for developing countries

Company Website Focus Funding source

Cepheid http://www.cepheid.com/ DNA (TB) FIND, US gov.Claros Diagnostics http://www.clarosdx.com/ Proteins PrivateHandyLab http://www.handylab.com/ DNA, proteins NIST, privateiStat http://www.istat.com/ Clinical chemistry markers PrivateLabNow http://www.labnow.com/ CD4 for HIV/AIDS George Soros, privateMicronics http://www.micronics.net/ Enteric disease pathogens PATH, University of Washington,

NIH, Gates FoundationNanogen http://www.nanogen.com/ Cardiac biomarkers, DNA/RNA PrivateNanosphere http://www.nanosphere-inc.com/ DNA, proteins NIAID, NIH, privateSensata http://www.sensata.com/ Proteins, viruses, bacteria PrivateSequella http://www.sequella.com/ Proteins (TB) Private

Table 4 Sample list of NGOs focusing on the development of new diagnostics for global health

NGOs Website Focus Year Founded

FIND http://www.finddiagnostics.org/ TB 2003PATH http://www.path.org/ Diarrheal diseases, malaria, STIs,

AIDS, and cervical cancer1977

Tuberculosis Diagnostics Initiative http://www.who.int/tdr/diseases/tb/tbdi.htm TB 1996WHO Malaria Rapid Diagnostics Tests http://www.wpro.who.int/sites/rdt Malaria 2005WHO Sexually Transmitted Diseases

Diagnostic Initiativehttp://www.who.int/std_diagnostics/ Chlamydia, gonorrhea, syphilis 2001

WHO/TDR http://www.who.int/tdr/ TB, AIDS, malaria, STIsa 1975a Abbreviation: sexually transmitted infections (STIs).

54 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

In the long term, miniaturization of medical technologies

has the potential to improve public health, and perhaps even

change the basic methods by which patients are diagnosed and

treated, in developing countries. This pathway has a well-

known precedent in information and communication tech-

nologies. Over the last 10 years in developing countries,

adoption of cell phones and wireless internet has resulted in

‘leapfrogging’ over conventional communication technologies

(such as landlines) that require significant infrastructure.52 In

the next 10 years, will LOC methods follow a similar path, by

promoting in developing countries a leapfrog over conven-

tional medical technologies (such as radiology, microbiological

culture, and centralized testing centers)?

Acknowledgements

We acknowledge Roberto Delatour from Medecins Sans

Frontieres and George Whitesides for helpful discussions,

Benjamin Wang for help on the figures, and Andreas Martinez

for help in compiling Table 1. This work was supported by an

Early Career Award from the Wallace H. Coulter Foundation.

References

1 A. S. Daar, H. Thorsteinsdottir, D. K. Martin, A. C. Smith,S. Nast and P. A. Singer, Nat. Genet., 2002, 32, 229–232.

2 H. Varmus, R. Klausner, E. Zerhouni, T. Acharya, A. S. Daarand P. A. Singer, Science, 2003, 302, 398–399.

3 A. Alwan and B. Modell, Nat. Rev. Genet., 2003, 4, 61–68.4 J. Sachs, Macroeconomics and Health: Investing in Health for

Economic Development, World Health Organization, Geneva,Switzerland, 2001.

5 R. Laxminarayan, A. J. Mills, J. G. Breman, A. R. Measham,G. Alleyne, M. Claeson, P. Jha, P. Musgrove, J. Chow, S. Shahid-Salles and D. T. Jamison, Lancet, 2006, 367, 1193–1208.

6 B. H. Robertson and J. K. A. Nicholson, Annu. Rev. PublicHealth, 2005, 26, 281–302.

7 C. J. L. Murray and A. D. Lopez, Lancet, 1997, 349, 1498–1504.8 C. J. L. Murray and A. D. Lopez, Lancet, 1997, 349, 1436–1442.9 World Bank World Development Report 1993: Investing in Health,

Oxford University Press, New York, NY, 1993.10 A. Lopez, C. Mathers, M. Ezzati, D. Jamison and C. Murray,

Global Burden of Disease and Risk Factors, Oxford UniversityPress and the World Bank, New York, NY, 2006.

11 D. H. Molyneux, P. J. Hotez and A. Fenwick, PLoS Med., 2005,2, 1064–1070.

12 E. Torreele, C. Royce, R. Don, A. M. Sevcsik and S. Croft, PLoSMed., 2006, 3, e282.

13 P. J. Hotez, D. H. Molyneux, A. Fenwick, E. Ottesen,S. Ehrlich Sachs and J. D. Sachs, PLoS Med., 2006, 3, e102.

14 D. Mabey, R. W. Peeling, A. Ustianowski and M. D. Perkins,Nat. Rev. Microbiol., 2004, 2, 231–240.

15 H. H. Lee and J. P. Allain, Vox Sang., 2004, 87, 176–179.16 R. Beaglehole and D. Yach, Lancet, 2003, 362, 903–908.17 J. C. Seidell, Br. J. Nutr., 2000, 83, S5–S8.

18 J. L. Deen, T. Vos, S. R. Huttly and J. Tulloch, Bull. W. H. O.,1999, 77, 518–524.

19 S. N. Forjuoh and G. Li, Soc. Sci. Med, 1996, 43, 1551–1560.20 I. R. Lauks, Acc. Chem. Res., 1998, 31, 317–324.21 A. J. Tudos, G. A. J. Besselink and R. B. M. Schasfoort, Lab

Chip, 2001, 1, 83–95.22 P. Belgrader, S. Young, B. Yuan, M. Primeau, L. A. Christel,

F. Pourahmadi and M. A. Northrup, Anal. Chem., 2001, 73,391–391.

23 C. T. Culbertson, Y. Tugnawat, A. R. Meyer, G. T. Roman,J. M. Ramsey and S. R. Gonda, Anal. Chem., 2005, 77,7933–7940.

24 A. M. Skelley, J. R. Scherer, A. D. Aubrey, W. H. Grover,R. H. C. Ivester, P. Ehrenfreund, F. J. Grunthaner, J. L. Badaand R. A. Mathies, Proc. Natl. Acad. Sci. U. S. A., 2005, 102,1041–1046.

25 T. Akiyama, S. Gautsch, N. F. de Rooij, U. Staufer,P. Niedermann, L. Howald, D. Muller, A. Tonin, H. R. Hidber,W. T. Pike and M. H. Hecht, Sens. Actuators, A, 2001, 91,321–325.

26 H. Becker and C. Gartner, Electrophoresis, 2000, 21, 12–26.27 J. Janata, Proc. IEEE, 2003, 91, 864–869.28 A. J. Ricco, T. D. Boone, Z. H. Fan, I. Gibbons, T. Matray,

S. Singh, H. Tan, T. Tian and S. J. Williams, Biochem. Soc.Trans., 2002, 30, 73–78.

29 A. de Mello, Lab Chip, 2002, 2, 31N–36N.30 K. R. Hawkins and P. Yager, Lab Chip, 2003, 3, 248–252.31 E. Garcia, J. R. Kirkham, A. V. Hatch, K. R. Hawkins and

P. Yager, Lab Chip, 2004, 4, 78–82.32 V. Linder, S. K. Sia and G. M. Whitesides, Anal. Chem., 2005, 77,

64–71.33 J. Moorthy, G. A. Mensing, D. Kim, S Mohanty, D. T. Eddington,

W. H. Tepp, E. A. Johnson and D. J. Beebe, Electrophoresis,2004, 25, 1705–1713.

34 Y. Li, P. Denny, C. M. Ho, C. Montemagno, W. Shi, F. Qi,B. Wu, L. Wolinsky and D. T. Wong, Adv. Dent. Res., 2005, 18,3–5.

35 V. Srinivasan, V. K. Pamula and R. B. Fair, Lab Chip, 2004, 4,310–315.

36 A. J. de Mello and N. Beard, Lab Chip, 2003, 3, 11N–19N.37 S. S. Shevkoplyas, T. Yoshida, L. L. Munn and M. W. Bitensky,

Anal. Chem., 2005, 77, 933–937.38 J. P. Brody and P. Yager, Sens. Actuators, A, 1997, 58, 13–18.39 S. Song, A. K. Singh, T. J. Shepodd and B. J. Kirby, Anal. Chem.,

2004, 76, 2367–2373.40 S. Song and A. K. Singh, Anal. Bioanal. Chem., 2006, 384, 41–43.41 R. H. Liu, M. A. Stremler, K. V. Sharp, M. G. Olsen,

J. G. Santiago, R. J. Adrian, H. Aref and D. J. Beebe,J. Microelectromech. Syst., 2000, 9, 190–197.

42 T. Rohr, C. Yu, M. H. Davey, F. Svec and J. M. J. Frechet,Electrophoresis, 2001, 22, 3959–3967.

43 P. Sethu, L. L. Moldawer, M. N. Mindrinos, P. O. Scumpia,C. L. Tannahill, J. Wilhelmy, P. A. Efron, B. H. Brownstein,R. G. Tompkins and M. Toner, Anal. Chem., 2006, 78,5453–5461.

44 S. K. Sia, V. Linder, B. A. Parviz, A. Siegel and G. M. Whitesides,Angew. Chem., Int. Ed., 2004, 43, 498–502.

45 D. Juncker, H. Schmid, U. Drechsler, H. Wolf, M. Wolf,B. Michel, N. de Rooij and E. Delamarche, Anal. Chem., 2002,74, 6139–6144.

Table 5 Sample list of organizations that sell or provide low-cost diagnostic instruments to developing countries

Organization Website Focus

Binax, Inc. http://www.binax.com/ ICTsa for malaria, influenza, filariasis, pneumonia, strep AGede Foundation http://www.gedefoundation.org/ AIDS-related diagnostics (flow cytometry, real-time PCR, hematology

analyzer, genotyping services)Human GmbH http://www.human.de/ Various (clinical chemistry and hematology analyzer, microscopy, ELISA)Partec http://www.partec.de/ Flow cytometrySustainable Sciences

Initiativehttp://www.ssilink.org/ Various (low-cost PCR, antibody-detection)

a Abbreviation: immunochromatographic tests (ICTs).

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 55

46 D. L. L. Chen and R. F. Ismagilov, Curr. Opin. Chem. Biol., 2006,10, 226–231.

47 S. Cesaro-Tadic, G. Dernick, D. Juncker, G. Buurman,H. Kropshofer, B. Michel, C. Fattinger and E. Delamarche,Lab Chip, 2004, 4, 563–569.

48 S. K. Sia and G. M. Whitesides, Electrophoresis, 2003, 24,3563–3576.

49 X. Jiang, J. M. Ng, A. D. Stroock, S. K. Dertinger andG. M. Whitesides, J. Am. Chem. Soc., 2003, 125, 5294–5295.

50 T. A. Taton, C. A. Mirkin and R. L. Letsinger, Science, 2000, 289,1757–1760.

51 S. J. Park, T. A. Taton and C. A. Mirkin, Science, 2002, 295,1503–1506.

52 United Nations Development Programme, Human DevelopmentReport 2001: Making New Technologies Work for HumanDevelopment, Oxford University Press, New York, NY, 2001.

53 S. L. Hart and C. M. Christensen, MIT Sloan Manage. Rev.,2002, 44, 51–56.

54 M. Usdin, M. Guillerm and P. Chirac, Nature, 2006, 441,283–284.

55 M. Cheesbrough, District Laboratory Practice in TropicalCountries, Part 1, Cambridge University Press, Cambridge, UK,2000.

56 M. Cheesbrough, District Laboratory Practice in TropicalCountries, Part 2, Cambridge University Press, Cambridge, UK,2000.

57 D. D. Cunningham, Anal. Chim. Acta, 2001, 429, 1–18.58 C. E. Michel, A. W. Solomon, J. P. Magbanua, P. A. Massae,

L. Huang, J. Mosha, S. K. West, E. C. Nadala, R. Bailey,C. Wisniewski, D. C. Mabey and H. H. Lee, Lancet, 2006, 367,1585–1590.

59 N. Christodoulides, S. Mohanty, C. S. Miller, M. C. Langub,P. N. Floriano, P. Dharshan, M. F. Ali, B. Bernard,D. Romanovicz, E. Anslyn, P. C. Fox and J. T. McDevitt, LabChip, 2005, 5, 261–269.

60 B. H. Weigl, J. Gerdes, P. Tarr, P. Yager, L. Dillman, R. Peck,S. Ramachandran, M. Lemba, M. Kokoris, M. Nabavi,F. Battrell, D. Hoekstra, E. J. Klein and D. M. Denno, Proc.SPIE—Int. Soc. Opt. Eng., 2006, 6112, 1–11.

61 A. D. Stroock, S. K. W. Dertinger, A. Ajdari, I. Mezic,H. A. Stone and G. M. Whitesides, Science, 2002, 295, 647–651.

62 P. Garstecki, J. F. M, M. A. Fischbach, S. K. Sia andG. M. Whitesides, Lab Chip, 2006, 6, 207–212.

63 A. P. Sudarsan and V. M. Ugaz, Proc. Natl. Acad. Sci. U. S. A.,2006, 103, 7228–7233.

64 A. Bernard, B. Michel and E. Delamarche, Anal. Chem., 2001, 73,8–12.

65 M. Wolf, D. Juncker, B. Michel, P. Hunziker and E. Delamarche,Biosens. Bioelectron., 2004, 19, 1193–1202.

66 D. B. Weibel, M. Kruithof, S. Potenta, S. K. Sia, A. Lee andG. M. Whitesides, Anal. Chem., 2005, 77, 4726–4733.

67 E. Garcia, J. R. Kirkham, A. V. Hatch, K. R. Hawkins andP. Yager, Lab Chip, 2003, 4, 78–82.

68 J. V. Zoval and M. J. Madou, Proc. IEEE, 2004, 92, 140–153.69 M. J. Pugia, G. Blankenstein, R. P. Peters, J. A. Profitt, K. Kadel,

T. Willms, R. Sommer, H. H. Kuo and L. S. Schulman, Clin.Chem., 2005, 51, 1923–1932.

70 N. Honda, U. Lindberg, P. Andersson, S. Hoffman and H. Takei,Clin. Chem., 2005, 51, 1955–1961.

71 S. A. Lange, G. Roth, S. Wittemann, T. Lacoste, A. Vetter,J. Grassle, S. Kopta, M. Kolleck, B. Breitinger, M. Wick,J. K. Horber, S. Dubel and A. Bernard, Angew. Chem., Int. Ed.,2005, 45, 270–273.

72 F. S. Ligler and J. S. Erickson, Nature, 2006, 440, 159–160.73 J. M. Nam, C. S. Thaxton and C. A. Mirkin, Science, 2003, 301,

1884–1886.74 J. Schupbach, AIDS Rev., 2002, 4, 83–92.75 J. Homola, S. S. Yee and G. Gauglitz, Sens. Actuators, B, 1999,

54, 3–15.76 T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser

and J. L. Elkind, Sens. Actuators, B, 2003, 91, 266–274.77 A. N. Naimushin, S. D. Soelberg, D. K. Nguyen, L. Dunlap,

D. Bartholomew, J. Elkind, J. Melendez and C. E. Furlong,Biosens. Bioelectron., 2002, 17, 573–584.

78 T. Aytur, J. Foley, M. Anwar, B. Boser, E. Harris and R. Beatty,J. Immunol. Methods, 2006, 314(1–2), 21–29.

79 J. A. M. Vet, A. R. Majithia, S. A. E. Marras, S. Tyagi, S. Dube,B. J. Poiesz and F. R. Kramer, Proc. Natl. Acad. Sci. U. S. A.,1999, 96, 6394–6399.

80 D. Candotti, J. Temple, S. Owusu-Ofori and J. P. Allain, J. Virol.Methods, 2004, 118, 39–47.

81 C. Drosten, M. Panning, J. F. Drexler, F. Hansel, C. Pedroso,J. Yeats, L. K. de Souza Luna, M. Samuel, B. Liedigk, U. Lippert,M. Sturmer, H. W. Doerr, C. Brites and W. Preiser, Clin. Chem.,2006, 52, 1258–1266.

82 F. Rouet, D. K. Ekouevi, M. L. Chaix, M. Burgard, A. Inwoley,T. D. Tony, C. Danel, X. Anglaret, V. Leroy, P. Msellati, F. Dabisand C. Rouzioux, J. Clin. Microbiol., 2005, 43, 2709–2717.

83 J. Coloma and E. Harris, Br. Med. J., 2004, 329, 1160–1162.84 P. A. Auroux, Y. Koc, A. deMello, A. Manz and P. J. R. Day,

Lab Chip, 2004, 4, 534–546.85 L. C. Waters, S. C. Jacobson, N. Kroutchinina, J. Khandurina,

R. S. Foote and J. M. Ramsey, Anal. Chem., 1998, 70, 158–162.86 J. W. Hong, V. Studer, G. Hang, W. F. Anderson and S. R. Quake,

Nat. Biotechnol., 2004, 22, 435–439.87 Y. Huang, E. L. Mather, J. L. Bell and M. Madou, Anal. Bioanal.

Chem., 2002, 372, 49–65.88 J. S. Marcus, W. F. Anderson and S. R. Quake, Anal. Chem.,

2006, 78, 3084–3089.89 R. H. Liu, J. N. Yang, R. Lenigk, J. Bonanno and P. Grodzinski,

Anal. Chem., 2004, 76, 1824–1831.90 M. A. Burns, B. N. Johnson, S. N. Brahmasandra, K. Handique,

J. R. Webster, M. Krishnan, T. S. Sammarco, P. M. Man,D. Jones, D. Heldsinger, C. H. Mastrangelo and D. T. Burke,Science, 1998, 282, 484–487.

91 M. A. Northrup, B. Benett, D. Hadley, P. Landre, S. Lehew,J. Richards and P. Stratton, Anal. Chem., 1998, 70, 918–922.

92 J. Y. Lee, J. J. Kim and T. H. Park, Biotechnol. Bioprocess Eng.,2003, 8, 213–220.

93 J. S. Marcus, W. F. Anderson and S. R. Quake, Anal. Chem.,2006, 78, 956–958.

94 E. T. Lagally, J. R. Scherer, R. G. Blazej, N. M. Toriello,B. A. Diep, M. Ramchandani, G. F. Sensabaugh, L. W. Riley andR. A. Mathies, Anal. Chem., 2004, 76, 3162–3170.

95 J. N. Yang, Y. J. Liu, C. B. Rauch, R. L. Stevens, R. H. Liu,R. Lenigk and P. Grodzinski, Lab Chip, 2002, 2, 179–187.

96 M. U. Kopp, A. J. Mello and A. Manz, Science, 1998, 280,1046–1048.

97 Z. Chen, S. Qian, W. R. Abrams, D. Malamud and H. H. Bau,Anal. Chem., 2004, 76, 3707–3715.

98 M. Krishnan, V. M. Ugaz and M. A. Burns, Science, 2002, 298,793–793.

99 T. Tang, M. Y. Badal, G. Ocvirk, W. E. Lee, D. E. Bader,F. Bekkaoui and D. J. Harrison, Anal. Chem., 2002, 74,725–733.

100 Y. Hataoka, L. Zhang, Y. Mori, N. Tomita, T. Notomi andY. Baba, Anal. Chem., 2004, 76, 3689–3693.

101 A. Gulliksen, L. A. Solli, K. S. Drese, O. Sorensen, F. Karlsen,H. Rogne, E. Hovig and R. Sirevag, Lab Chip, 2005, 5, 416–420.

102 M. Vincent, Y. Xu and H. M. Kong, EMBO Rep., 2004, 5,795–800.

103 S. Tyagi and F. R. Kramer, Nat. Biotechnol., 1996, 14, 303–308.104 S. Tyagi, S. A. E. Marras and F. R. Kramer, Nat. Biotechnol.,

2000, 18, 1191–1196.105 M. Culha, D. L. Stokes, G. D. Griffin and T. Vo-Dinh, Biosens.

Bioelectron., 2004, 19, 1007–1012.106 M. Culha, D. L. Stokes, G. D. Griffin and T. Vo-Dinh, J. Biomed.

Opt., 2004, 9, 439–443.107 T. G. Drummond, M. G. Hill and J. K. Barton, Nat. Biotechnol.,

2003, 21, 1192–1199.108 M. A. Dineva, D. Candotti, F. Fletcher-Brown, J. P. Allain and

H. Lee, J. Clin. Microbiol., 2005, 43, 4015–4021.109 D. Huh, W. Gu, Y. Kamotani, J. B. Grotberg and S. Takayama,

Physiol. Meas., 2005, 26, R73–98.110 P. Mwaba, S. Cassol, R. Pilon, C. Chintu, M. Janes, A. Nunn and

A. Zumla, Lancet, 2003, 362, 1459–1460.111 A. Y. Fu, H. P. Chou, C. Spence, F. H. Arnold and S. R. Quake,

Anal. Chem., 2002, 74, 2451–2457.

56 | Lab Chip, 2007, 7, 41–57 This journal is � The Royal Society of Chemistry 2007

112 A. Goodey, J. J. Lavigne, S. M. Savoy, M. D. Rodriguez,T. Curey, A. Tsao, G. Simmons, J. Wright, S. J. Yoo, Y. Sohn,E. V. Anslyn, J. B. Shear, D. P. Neikirk and J. T. McDevitt,J. Am. Chem. Soc., 2001, 123, 2559–2570.

113 W. R. Rodriguez, N. Christodoulides, P. N. Floriano, S. Graham,S. Mohanty, M. Dixon, M. Hsiang, T. Peter, S. Zavahir, I. Thior,D. Romanovicz, B. Bernard, A. P. Goodey, B. D. Walker andJ. T. McDevitt, PLoS Med., 2005, 2, e182.

114 M. Fryland, P. Chaillet, R. Zachariah, A. Barnaba, L. Bonte,R. Andereassen, S. Charrondiere, R. Teck and O. Didakus,Trans. R. Soc. Trop. Med. Hyg., 2006, 100, 980–985.

115 I. V. Jani, G. Janossy, D. W. Brown and F. Mandy, Lancet Infect.Dis., 2002, 2, 243–250.

116 A. G. J. Tibbe, B. G. de Grooth, J. Greve, P. A. Liberti,G. J. Dolan and L. W. M. M. Terstappen, Cytometry, 2001, 43,31–37.

117 N. Christodoulides, P. N. Floriano, S. A. Acosta, K. L. M. Ballard,S. E. Weigum, S. Mohanty, P. Dharshan, D. Romanovicz andJ. T. McDevitt, Clin. Chem., 2005, 51, 2391–2395.

118 J. P. Shelby, J. White, K. Ganesan, P. K. Rathod and D. T. Chiu,Proc. Natl. Acad. Sci. U. S. A., 2003, 100, 14618–14622.

119 P. Gascoyne, J. Satayavivad and M. Ruchirawat, Acta Trop.,2004, 89, 357–369.

120 F. K. Balagadde, L. You, C. L. Hansen, F. H. Arnold andS. R. Quake, Science, 2005, 309, 137–140.

121 N. Futai, W. Gu, J. W. Song and S. Takayama, Lab Chip, 2006, 6,149–154.

122 S. Petronis, M. Stangegaard, C. B. Christensen and M. Dufva,Biotechniques, 2006, 40, 368–376.

123 X. Heng, D. Erickson, L. R. Baugh, Z. Yaqoob, P. W. Sternberg,D. Psaltis and C. Yang, Lab Chip, 2006, 6, 1274.

124 M. H. Hazbon, N. Guarin, B. E. Ferro, A. L. Rodriguez,L. A. Labrada, R. Tovar, P. F. Riska and W. R. Jacobs, J. Clin.Microbiol., 2003, 41, 4865–4869.

125 G. T. A. Kovacs, Micromachined Transducers Sourcebook,McGraw-Hill, New York, 1998.

126 M. Madou, Fundamentals of Microfabrication, CRC Press, BocaRaton, FL, 1998.

127 I. H. A. Badr, R. D. Johnson, M. J. Madou and L. G. Bachas,Anal. Chem., 2002, 74, 5569–5575.

128 H. Hisamoto, M. Yasuoka and S. Terabe, Anal. Chim. Acta, 2006,556, 164–170.

129 B. H. Lapizco-Encinas, B. A. Simmons, E. B. Cummings andY. Fintschenko, Anal. Chem., 2004, 76, 1571–1579.

130 P. S. Dittrich and A. Manz, Nat. Rev. Drug Discovery, 2006, 5,210–218.

131 P. A. Singer and A. S. Daar, Science, 2001, 294, 87–89.132 F. Salamanca-Buentello, D. L. Persad, E. B. Court, D. K. Martin,

A. S. Daar and P. A. Singer, PLoS Med., 2005, 2, 383–386.133 N. Tsapis, D. Bennett, B. Jackson, D. A. Weitz and D. A.

Edwards, Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 12001–12005.134 D. A. LaVan, T. McGuire and R. Langer, Nat. Biotechnol., 2003,

21, 1184–1191.135 J. Z. Hilt and N. A. Peppas, Int. J. Pharm., 2005, 306, 15–23.136 E. Rodgers, Diffusion of Innovations, the Free Press, New York,

4th edn, 1995.137 P. Yager, T. Edwards, E. Fu, K. Helton, K. Nelson, M. R. Tam

and B. H. Weigl, Nature, 2006, 442, 412–418.138 Frost & Sullivan Report: United States In Vitro Cancer Diagnostics

Market, Frost & Sullivan, March 1, 1999.139 C. H. Ahn, J. W. Choi, G. Beaucage, J. H. Nevin, J. B. Lee,

A. Puntambekar and J. Y. Lee, Proc. IEEE, 2004, 92, 154–173.

This journal is � The Royal Society of Chemistry 2007 Lab Chip, 2007, 7, 41–57 | 57