amplifies the current signals into a readable digital display in the readout device [3].

Figure 22.1 gives a schematic representation of the workings of the biosensor device.

22.1.1 Categories of Biosensors

22.1.1.1 Classification Based on Bioreceptor

As shown in Figure 22.1, mainly five kinds of bioreceptors are used for the fabrication of

biosensors. Based on these, there are different types:

1. Enzyme-based biosensor: In these, an enzyme is used as a bioreceptor over the

matrix. This can detect a specific analyte substrate that can compatibly bind with

the enzyme. It has a lock and key model. Enzymes are target analyte-specific.

Enzymes that can recognize the analytes are effective biocatalysts. For instance,

glucose oxidase for glucose, urease for urea, peroxidases for peroxide, etc. The

analyte detection depends upon the attributes like enzyme changing the analyte to

a detectable form, pH, temperature, substrate concentration, enzyme concentra­

tion, etc. Although enzyme-based biosensors are highly selective and specific, there

are certain limitations related to stability and adaptability [4].

2. Antibody/immunosensor: These biosensors are used for pathogen and infection

analysis. An antibody (Immunoglobin-Ig) is a bioreceptor and is used for the de­

tection of diseases and biomarkers like cancer, cardiovascular diseases, hepatitis, etc.

Ig is a target antigen-specific and is immobilized on the matrix. Ig binds with the

antigen to form an antigen-antibody complex, which causes electron shuttling [5].

3. DNA-based biosensor: Herein, complementary DNA strands, usually single strands,

are used as the bioreceptors on the matrix. The target analyte DNA is denatured

chemically and mixed with the electrolyte. The matching sequence identifies this

strand and forms double-stranded DNA bond causing electron transfer [6].

4. Cell-based biosensors: Herein, live microorganisms cells like bacteria and fungi

are used as bioreceptors over the matrix. These measures intracellular and ex­

tracellular parameters. The major limitation is stability and contamination [7].

5. Biomimetric biosensor: Here, synthetic DNA sequences, called aptamers, are

used as bioreceptors over the matrix, which mimic the natural DNA sequence.

These are used for the detection of proteins, amino acids, etc. These are slightly

advantageous as they can be manipulated as needed [8].

FIGURE 22.1

Schematic representation of biosensor components and working principle.

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Bioelectronics