BIOSENSORS

In Defense Shreya JohnM.Phil.

Biotechnology

WHAT ARE BIOSENSORS?• Biosensor is an analytical device

containing biological sensing - biorecognition – element in a close contact with a transducer.• The interaction between the

biorecognition element and analyte changes the physical properties which are converted by the transducer into electric signal, and finally detected by some data processing unit.

BIOSENSORS AGAINST TERRORISM??

• Terrorism does not always use lethal weapons such as high end guns, tanks, missiles, dynamites, bombs, nuclear weapons, etc. sometimes they also use biological weapons.• These biological weapons are intentional release or

dissemination of biological agents. These agents are bacteria, viruses, or toxins (otherwise known as biological warfare).• Hence, it is known as ‘Bioterrorism’.

TRAGIC EVENTS CAUSED BY CHEMICAL AND BIOLOGICAL TOXINS (CBTS)

Several tragic events have happened in the past, and are recurring:• Minamata disaster (1932-1968, Japan) due to mercury release, • Seveso disaster (1976, Italy) due to dioxin release, • Bhopal tragedy (1984, India) due to methyl isocynate gas leak, • Level seven nuclear disasters in Chernobyl (1986, Ukraine) and

more recently in Fukushima Daiichi (2011, Japan)• Plague (1994, India; 2006, Congo), flu (2009, worldwide), cholera

(2010, Haiti)

BIOSENSORS IN DEFENSE

• One of the applications of biosensors is in the area of defense.• For detection of BWA (Biological warfare), sensors with

immobilized antigen or antibody are used. • The most commonly used physicochemical transducers

include electrochemical, optical and piezoelectric sensors (Miroslav Pohanka et al., 2007).

Figure 1: Classification of technologies for the detection of chemical and biological toxins (CBTs) in the context of warfareagents and industrial-toxins. The techniques enclosed in brackets are the most successful and promising techniques for detection of warfare-agents. Optical biosensors, which are based on physical techniques is shown

separately (Bhardwaj and McGoron, 2014).

CONVENTIONAL TECHNIQUES

• The first literature evidence of technique for the detection and protection against toxins responsible for smallpox was reported in Philosophical Transactions of the Royal Society in 1714 (Taylor, 1714).

• Robert Koch and Louis Pasteur first reported the use of microbial culturing methods for identification of pathogenic agents for anthrax, tuberculosis and cholera, and the development of vaccine against them during 1870s (Brock, 1999).

Microbial assays

• Identifies new and existing biological warfare agents (BWAs) and the vaccines against them (Murray et al., 2003; Lim et al., 2005).

• Takes a day to a month.

The Ames test

• Validates new techniques to identify mutagens (Terziyaska et al., 2000; Knight et al., 2004; Yang et al., 2005).

Commercially available

biosensors• VITEK and API

series (bioMerieux, U.S.A.)

• MicroLog (BioLOG, U.S.A.)

• Microbial Identification Systems (MIDI Inc. U.S.A.)

ADVANCED BIOSENSOR TECHNOLOGIES

The most commonly used physicochemical transducers include Electrochemical sensors, optical sensors and piezoelectric sensors

ELECTROCHEMICAL BIOSENSORS

• Low cost and good sensitivity.• Several types of electrochemical biosensors are utilised:

Potentiometric, amperometric, and impedimetric. • Potentiometric biosensors - based on ion-selective electrodes.• Working Principle - These devices measure the change in ion

concentration during reaction taking place in the biorecognition layer.• Very popular semiconductor-based biosensors are light-addressable

potentiometric sensors (LAPS).

• The LAPS immunosensors were used to detect Francisella tularensis (Thompson et al., 1992) with a limit of detection (LOD) at 3.4 × 103 cells/ml and Bacillus melitensis with LOD equal to 6 × 103 cells/ml during the 1 h incubation time (Lee et al., 1993).

• The commercial system Bio-Detector, based on 8-channel LAPS, was developed by Smith Detection (Warrington, UK).

• This device intended for mobile laboratories is able to detect bacterial pathogens such as Bacillus anthracis with LOD 103 Cells/ml and toxins such as botulotoxin with LOD 0.1 ng/ml in 15 min.

PHYSICAL : OPTICAL BIOSENSORS

• Gives information on changes in physical properties, thermal, mechanical, optical etc., of cells in response to toxins.

Optical Biosensors

Surface Plasmon Resonance (SPR)

Resonant Mirror (RM)

Convenient for direct detection of bacteria without any label as well as for serotypization (Miroslav Pohanka et al., 2007).

SPR Biosensors

Used for detection of-• Bacillus anthracis (Tim

et al., 2004)• HIV (Bringham-Burke et

al., 1992)• Clostridium perfringens

beta-toxin (Hsieh et al., 1998)

RM BiosensorsApplied for-• Staphylococcus

aureus assay

Commercially available devices

• Bioward 1• BIAcore

PIEZOELECTRIC BIOSENSORS

• Convenient for label-free and real-time monitoring of interactions between antibody and antigen.

• Predominantly quartz crystal microbalance (QCM) is used.

• This sensor is produced by International Crystal Manufacturing (www.icmfg.com).

• Working principle - The change of resonance frequency recorded is proportional to the mass bound on the crystal surface.

• Commercial crystals have typically two gold electrodes on the opposite sides.

• Direct monitoring of cell concentration using monoclonal antibody immobilized through protein A to the gold electrode allows to detect 105 cells/ml of Salmonella typhimurium (Prusak-Sochaczewski et al., 1990) and 106 cells/ml of Escherichia coli in drinking water (Plomer et al., 1992).

• Wong et al. (1992), developed the QCM sensor for Salmonella species with immobilised monoclonal antibody, it was possible to detect 104 cells/ml.

• Carter et al. (1995), was able to detect 105 cells/ml of Vibrio cholerae.• The horse polyclonal antibody was used for the detection of SARS-

associated corona virus (Zuo et al., 2004).• QCM with immobilised antigen was used for Francisella tularensis assay

as immunoprecipitate with monoclonal IgM antibody providing LOD of 5 × 105 cells/ml within 30 min (Pohanka et al., 2005).

CONCLUSION

• Biosensors provided similar sensitivity as provided by other conventional detection instruments and techniques.

• Some biosensors reached even detection limits similar to the PCR techniques.

• Typical time of immunodetection is 15 min, but some devices like resonant mirror, quartz crystal microbalance are able to provide signal within 5 min.

• Biosensors can be used for detection of bacteria and viruses as well as toxins.

• Due to their small size and low cost, biosensors are convenient not only for laboratory routine but also for mobile laboratories and portable systems in the field.