Thermistor, microbe

Figure 5. Thermogram obtained with the microbe thermistor following introduction of various metabolites and inhibitors dissolved in 0.1 M potassium phosphate buffer pH 7.0 into the flow. The arrows indicate addition of a, ImM glucose b, buffer c, ImM glucose + ImM 2,4-dinitrophenol d, ImM glucose e, ImM glucose + 2mM arsenate f, buffer. The steady-state response to ImM glucose is set as 100% (15).

Using the microbe thermistor (J 5) it was possible to determine glucose concentrations in the perfusion medium. Fig. 8. The response was slower than is the case when purified enzyme preparations were used (34). 

Using cells entrapped in polyacrylamide, glucose could be determined. However, severe diffusional restrictions of the system resulted in rather low sensitivity of the system. In this method as well as in the one using a microbe thermistor (15), better analytical resolution would be obtained provided tlie immobilization techniques used are satisfactory. 

Karube [389] has pioneered in the development of many bacterial electrodes based on this principle using various bacteria depending on the target analyte. Ion-selective electrodes for NH3, O2, CO2, H2S and have all been used in conjunction with immobilized whole cells. Riedel et al. [390] have recently demonstrated that preincubation of certain bacterial electrodes with the desired analyte (substrate) can enhance the sensitivity of a sensor toward that chemical by a factor of as much as 25. This induction approach may prove to be widely applicable. The shelf-life of a wholecell electrochemical sensor can extend up to several weeks with fully optimized storage conditions (low temperature, for example). Microbe thermistors (sensors that respond to the heat evolved during bacterial metabolism of a substrate) have also been developed, but these present problems once again with respect to analyte specificity,... 

Flygar L, Larsson P.-O, Danielsson B (1990) Control of an affinity purification procedure using a thermal biosensor. Biotechnol Bioeng 36 723 - 726 Gemeiner P,StefucaV,Welwardova, A,MichalkovaE,Welward L, Kurillova L, Danielsson B (1993) Direct determination of the cephalosporin transforming activity of immobilized cells with use of an enzyme thermistor. 1. Verification of the mathematical model. Enzyme Microb Technol 15 50-56... 

Stefuca V, Gemeiner P, Kurillova L, Danielsson B, Bales V (1990) Application of the enzyme thermistor to the direct estimation of intrinsic kinetics using the saccharose-immobilized invertase system. Enzyme Microb Technol 12 830 - 835 Stefuca V, Welwardova A, Gemeiner P, Jakubova A (1994) Application of enzyme flow microcalorimetry to the study of microkinetic properties of immobilized biocatalyst. Biotech-nolTech 8 497-502... 

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