JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Pharmacy III Year PHARMACEUTICAL BIOTECHNOLOGY Previous Question Paper (August/September-2021 - R17)

A biosensor is an analytical device that integrates a biological sensing element with a physical transducer to convert a biological response into a measurable electrical signal. The working principle involves three primary stages:

1. Recognition: The biological element (such as enzymes, antibodies, nucleic acids, or microorganisms) specifically interacts with the target analyte. This interaction is highly selective and results in a biochemical change, such as the production or consumption of ions, electrons, gases, or heat.
2. Transduction: The transducer converts the biochemical change into a quantifiable physical signal. Common types include electrochemical, optical, thermal, or piezoelectric transducers.
3. Signal Processing: The resulting signal is amplified and processed by electronic circuitry to provide a digital or analog output proportional to the concentration of the analyte.

The efficiency of the biosensor depends on the stability of the biological component and the sensitivity of the transducer in detecting the specific analyte-receptor binding event.

Amperometric Biosensors: These sensors measure the current generated by the oxidation or reduction of electroactive species at a constant potential applied to the working electrode. The current produced is directly proportional to the concentration of the analyte. A common example is the glucose biosensor, where glucose oxidase catalyzes the oxidation of glucose, and the resulting electron transfer is measured at the electrode surface.

Potentiometric Biosensors: These sensors measure the potential difference (voltage) between a working electrode and a reference electrode under conditions of zero current. The potential is related to the concentration of the analyte (usually ions) according to the Nernst equation. These sensors are highly sensitive to ion activity, such as H+, NH4+, or CO2. A classic example is the ion-selective electrode (ISE) or pH-sensitive field-effect transistor (pH-FET), where the accumulation of specific ions at the membrane surface creates a potential shift that is recorded as the analytical signal.