Enzyme Biosensors Based on Thermal Transducer/Thermistor

Abstract

Calorimetry is the measurement of heat accompanying a chemical or biochemical reaction (1, 2). The heat changes could be endothermic (absorption of heat) or exothermic (evolution of heat). In the early 1950s the technique of microcalorimetry was devised to measure the heat accompanying a biochemical reaction (3). After the initial elucidation of the concept, scanning microcalorimeters were designed to follow the heat changes accompanying folding and unfolding of protein molecules. The conventional microcalorimeters used sensitive thermocouples as the measurement device whereas the modern calorimeters, designed in the early 1970s, used thermistors, with a temperature sensitivity of 10⁻⁵–10⁻⁶°C. The evolution of calorimetric sensors (4, 5) included heat conduction, isoperibol, and more recently, isothermal calorimetry. The unique advantage of isothermal calorimetry involving thermistors is the fact that the heat evolved or absorbed during a biochemical reaction is a direct measure of the reaction, In the recent past, the concept has been extended to the design of miniaturized thermistor-based calorimeters, 50 mm in length and 15 mm in diameter or smaller.