using a high-concentration monomer for polymerization and bioreceptor

entrapment, leakage of bioreceptors is observed.

v. Encapsulation: In this, a semi-permeable membrane is used, which allows a

selective bioreceptor to seep in and form a capsule around it. An inexpensive

approach, but limitations in terms of pore size and permeability are observed.

22.1.1.2 Classification Based on Transducer

1. Electrochemical: Herein, a systematically modified electrode with various ma­

trices and chemicals or a non-modified electrode is used as a transducer.

Potentiostatic techniques like impedance, voltammetry, amperometry, and con­

ductometry are used to measure the signals.

2. Optical: In this, optics-dependent sensors act as transducers. Methods like ab­

sorption, fluorescence, phosphorescence, photomultiplier tube, etc. are utilized

for measuring the signals [10].

3. Calorimetric: Heat and temperature-based sensors are used. Changes in these

parameters are recorded as signals.

4. Piezoelectric: Materials like quartz that resonate at a particular frequency when it

comes in contact with the target analyte are used. The bioreceptor is also coated

with this piezoelectric substance. Upon reaction, the frequency is altered, which

is captured as signals.

22.1.1.3 Classification Based on Electron Transfer

Biosensors are divided into three major categories based upon the electron transfer

mechanism:

1. First-generation: These are mediator-less sensors. Herein, the analyte concentra­

tion or the product of the enzyme-analyte reaction is measured via diffusion to

FIGURE 22.3

Schematic representation of various immobilization approaches.

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Bioelectronics