Development of Some Biosensors and Their Analytical Applications

Abstract

The present work provides an insight into the concept, development, and application of the whole-cell biosensors for organophosphorus pesticide determination. For the fabrication of biosensor, Chlorella sp. algal cells having phosphatase activity were chosen. The reason for choosing algal cells as a sensor-modifying agent was their stability in quasi-physiological conditions, easy to handle, economical, high productivity and have a longer life span compared to bacterial or other whole cells. It is necessity for a biosensor that biological recognition element and transducer should work as a single unit, thus, immobilization becomes an important step for biosensor development. Our work has primarily focused on the fabrication of electrochemical biosensors. The algal cells with anticipated phosphatase enzyme were immobilized on the electrode surface using appropriate techniques. The immobilization technique solely depends upon the type of electrode used for preparation of biosensor. The thesis has been divided into two sections- (i) Inhibition based biosensors, (ii) Catalytic biosensors. Inhibition based biosensor are those in which pesticide concentration is determined by measuring the extent of inhibition of the enzyme activity. To increase sensitivity, operational stability, and to attain low detection limit, ZnO nanostructures have been introduced in the design of biosensor. Two types of biosensors have been developed under this section: (i) An electrochemical biosensor for the determination of acephate pesticide was developed based on algal modified silica coated ZnO quantum dots (QDs). The surface active alkaline phosphatase enzyme on the Chlorella sp. algae cell wall dephosphorylates substrate p-nitrophenyl phosphate (pNPP) and release p-nitrophenol (pNP), which being electroactive gets oxidized on the modified working electrode to generate current equivalent to the amount of pNP released from the substrate.