1.4_Microfluidics.ppt

8/19/2019 1.4_Microfluidics.ppt

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Microfluidics


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• Microfuidics systems – widely used in biomedical, precision

manuacturing processes and pharmaceutical industries.

• Principal application o microfuidics systems are in:

• Chemical analysis

• Biological and chemical sensing

• Drug deliery

• Molecular separation such as D!" analysis

• "mpli#cation

• $e%uencing or synthesis o nucleic acids and

• &nironmental monitoring.

• Microfuidics is also an essential part o precision control

systems or automotie, aerospace and machine tool

industries.

Microfluidics


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'. "bility to wor( with small samples, which leads to signi#cantly

smaller and less e)pensie biological and chemical analysis.

*. Most microfuidic systems o+er better perormance with

reduced power consumption.

. Most fuidic systems or biotechnical analyses can be

combined with traditional electronics systems on a singlepiece o silicon as a lab-on-a-chip /0C1.

2. $ince, many o these systems are produced in batches, they

are disposable ater use, which ensures saety in application

and saings in the costs o cleaning and maintenance.

Advantages of Microfluidics Systems


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• " microfuidic system consists o no33les, pumps, channels,

reseroirs, mi)ers, oscillators and ales in micro or meso

scales.

• 4eming '5561 de#nes the scope o microfuidics systems as

a fuidic system comprises the ollowing ma7or components.

•

Microsensors used to measure fuid properties pressure,temperature and fow1.

• Actuators li(e micro-ales, micro-pumps and compressors

are used to alter the stat o fuids.

• Distribution channels regulating fows in arious branches

in the system. &g. Capillary networ(s, microchannels o non-

circular cross section.

• 8hey typically hae open-cross sectional areas o µm2.

• 8he channels direct fuid fows o ew a ew hundred

Microfluidics System


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• Microchannels o non-circular cross-sections are usually

produced by chemical etching in open channels.

• 8wo open channels are bonded to proide the closed conduit.

• 8hese channels can be produced in lengths o less than a

millimeter.



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• &lectrodynamic orces are proided by electro-osmosis or

electrophoresis in bio testing and analytical systems are

e)tensiely used to drie the fuid.

• $ystems integration includes integrating the microsensors,

ales and pumps through the microchannel lin(s.

• 8his integration inoles the re%uired electrical systems that

proide electro-hydrodynamic orces, the circuits or

transduction and processing the electronic signals and control

o the microfuid fow in the system.

• Microfuidic systems can be built with a ariety o materials,

such as %uart3, glasses, plastics and polymers, ceramics,

semiconductors and metals.

• Design o microfuidic systems re%uires special considerations

eg. scaling law.• $urace-to-mass ratio chan es drasticall when the s stems



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• &lectrohydrodynamic pumping is an e+ectie way o moing

fuids in microchannels.

• ell-(nown !aier-$tro(es e%uations or fuid dynamics can

no longer be used in predicting the dynamics o fuid fow in

microsystems.

•

8hereore, theoretical ormulations are to be modi#ed in orderto apply or microchannel fows.



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• &4D deals with the motion o fuids drien by an electric #eld

applied to the fuids.

• 8here are two principal applications o &4D in microsystems.

• &lectro-osmotic pumping and electro-phoretic pumping.

• 8hese uni%ue techni%ues are used to moe chemical and

biological fuids in channels with e)tremely small cross-sections, ranging rom µm2 to mm2.

• ;low rates in such techni%ues will be in the order o µm3/s.

• Microfuidics are widely used in the pharmaceutical industry

and in biochemistry analysis using e)tremely small sample

%uantities in the order o ew hundred nanoliters.

• &4D pumping does not hae any moing mechanical parts

such as rotating impellers.

Electrohydrodynamics (EHD)


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• 0ten, it is the only e+ectie way to moe fuids in e)tremely

small channels because o the capillary e+ect.

• 8his e+ect in fuid fow in small conduits is principally due to

the surace tension and the an der aals orces in fuid

molecules.

•

Conse%uently, conentional olumetric mechanical pumpingcan not be e+ectiely used or the fuid moement through

these e)tremely small cross sections.

• 0ne speci#c application is the capillary electrophoresis C&1

process or rapid accurate chemical and biological analysis.

• ;ree electric charges in solents can be produced in seeral

ways.

• ;or eg. By electrolytes.

• Dielectric li%uids sub7ected to ery high oltage can produce



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• "nother way to generate charges is by electriying layered

li%uids with spatial gradients o electric conductiity and

permitiity as indicated in the ollowing e%uation Bart et al.

'55


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• ;ig. illustrates the generation o ionic solution in an electro-

osmotic pumping in a conduit Bart et al. '55


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• ;ree charges are produced by the gradient o electric

conductiity, which is presented by the di+erence in the

resistiities and the permitiities between the two materials.

• $igns o the surace charges in the material layer are

determined by the permitiities o the materials.

•

;or eg. 9 material layer ' were close to being an insulator,then the surace charge induced would be opposite to the

sign o the electrode array.

• 0nce ree charges are generated in the fuid, pumping o the

fuid along the longitudinal direction can be accomplished byapplying electric #eld to the electrodes in the array along the

length o the channel as shown.



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• =sed to moe electrically neutral fuids through channels o

e)tremely small cross-sections.

• Condition is that the wall o the conduit or channel must hae

attached immobile charges.

• " glass wall shown1 can produce such immobile charges

along the surace, i it is coated either with ioni3able materialsdeprotonated silanol groups1 or with strongly absorbed

charged species that are present in the fuid..

Electro-osmotic Pumping


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• 9n such cases, electro-osmotic motion o fuid in

microchannels o capillary tubes can be produced in any

electrolyte fuid.

• Because the gradient o the concentration o electric charges

decreases toward the centre o the conduit, a dual layer o

fuid with arying concentration o charges is ormed.

• Charges in the double layer can be moed with the applied

electric charges along the longitudinal direction.

• Momentum o the moing charges can drie the solent

through the fiud channel.• " uni%ue eature o electro-osmotic fow is that a uniorm

elocity pro#le o the moing fuid across the cross section o

the tube channel is obtained.

Electro-osmotic Pumping


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• =sed to separate minute oreign particles or species rom the

bul( fuid.

• Microfuidic systems with electrophoresis are widely used in

biomedical and pharmaceutical industries.

• Moement o ions o the particles in a hetrogenous medium is

prompted by an applied high-oltage electric #eld.• 9ons with di+erent charges moe in opposite directions along

the channel in the separation process.

• hen the fow is ully deeloped, the ions in the stream can

automatically separate themseles by their inherent electro-

osmotic mobility under the infuence o applied electric #eld.

• 9t is a highly desirable situation in chemical and biological

analyses, in which separation o arious minute species is

oten a di>cult tas(.

Electrophoretic Pumping


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Electrophoretic Pumping


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• ?ate o fow in both electro-osmotic and electro-phoretic

pumping is linearly proportional to the applied electric #eld.

• 8hese pumping methods inole no moing mechanical parts.

• 9t is especially suitable or miniaturi3ed systems.

• 0nly a small sample o analyte is re%uired in most cases with

this type o pumping in microfuidic systems.

• @elocity o moing ree charges in &4D pumping can be

determined with the ollowing e%uation Aoacs '5561.

EHD Pumping

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1.4_Microfluidics.ppt