Enzyme for biosensing applications

Abstract

Enzymes are very efficient biocatalysts, which have the ability to specifically recognize their substrates and to catalyze their transformation. These unique properties make the enzymes powerful tools to develop analytical devices. Enzyme-based biosensors associate intimately a biocatalyst-containing sensing layer with a transducer. The transformations catalyzed by an enzyme come with the variations of some physicochemical parameters. The role of the transducer is to convert those physicochemical signals into a measurable electrical signal. In biosensors, enzymes are generally immobilized on or close to the transducer. Depending on the chemical and physical characteristics of the enzyme support, different immobilization techniques can be implemented. The transduction mode will be adapted to the physicochemical parameter that is monitored. The variation of the concentration of a substrate or a product in the course of an enzymatic reaction can be detected with the help of a physical or chemical sensor, which then acts as a transducer. Electrochemical biosensors have been then developed involving oxidoreduction reactions. Optical biosensors are based either on fluorescence, absorbance, and bioluminescence or chemiluminescence measurements. Enzymatic reactions are usually associated with a high enthalpy change, which results in a temperature variation that can be recorded using a thermistor. Gravimetric biosensors are based on a mass variation induced by an enzymatic reaction. Due to their proteic nature, enzymes are often fragile and this instability results in a decrease in the enzyme activity and consequently in a decrease in the biosensor performances. Although, fortunately, not all enzymes are concerned, this can limit the development of enzyme-based biosensors. The first biosensors described were the size of a pH electrode but now the progress in the transducer technology makes the fabrication of miniaturized systems possible and this allows the development of small-sized multi-biosensors and the integration of miniaturized biosensors in lab-on-a-chip-type devices. © Springer Science+Business Media, LLC 2010.