RECENT DEVELOPMENTS OF BIOSENSORS BASED ON THERMISTORS AND SEMICONDUCTORS

Abstract

The enzyme thermistor (ET) is a simple flow calorimeter primarily intended for rapid metabolite assays with use of immobilized enzymes, but it can be used as a general biocalorimeter as well. The reaction heat produced in a small column containing immobilized biocatalyst is measured with a thermistor as a temperature change of the effluent of the column. The temperature change is linearjvs. the substrate) icon— centration over wide ranges from about 1 uM to several hundred mM depending on the actual enzyme reaction. Considerably higher sensitivities can be obtained by using recycling enzyme systems. Up to 60 samples per hour can be analyzed. A large number of metabolite assays of clinical as well as of biotechnological interest has been studied. The ET assay can easily be automated and is well suited for monitoring and control of biotechnological processes due to its high operational stability. For the monitoring of larger molecules a thermometric enzyme immunoassay (TELISA) has been developed and automated. Hydrogen- and ammonia-sensitive semiconductors of Pd-MOS type could be combined with enzymes and cells into highly sensitive biosensors. Addition of another catalytic metal, such as Ir on the gate of the MOSdevice results in enhanced ammonia-sensitivity. Highly sensitive methods for the determination of e.g. urea and creatinine have been developed. Detection is made in the gas phase, which is advantageous.