Highly sensitive enzyme thermistor determination of ADP and ATP by multiple recycling enzyme systems

Screening of concanavalin A-bead cellulose conjugates using an enzyme thermistor with immobilized invertase as the reporter catalyst

Screening and design of immobilized biocatalysts (IMBs) is a time-consuming process. An ideal process should be universal, fast, convenient, precise, and reproducible. Many of these requirements are met by enzymic flow microcalorimeters, also known as enzyme thermistors (ETs) or thermal assay probes (TAPs). Adaptation of ETs to real measurements of reaction rates requires coupling of the mathematical description of the reaction-diffusion phenomena in the ET column with heat balance and, subsequently, experimental verification of the mathematical model. This article presents such a process developed as an adaptation of ETs for the characterization of the microkinetic properties of IMBs and their further application for screening of IMBs. The IMBs characterized were the preparations of invertase, biospecificaly adsorbed on concanavalin A conjugated to activated bead cellulose. (c) 1994 John Wiley & Sons, Inc.

Thermal Biosensor and Microbiosensor Techniques

This chapter describes principles and features of thermal biosensors and microbiosensors and includes a discussion of different thermal transducers. A number of instrumental concepts are described in detail from larger flow injection instruments to miniaturized devices and chip designs with thermal arrays. A thermal–electrochemical hybrid sensor is also presented. The chapter contains many descriptions of actual assays from different fields, such as process and in vivo monitoring, multianalyte determination, operation in organic solvents, and environmental analysis.

Principles and applications of thermal biosensors

A review of thermistor-based calorimetric measurement is presented. The principles of thermometric measurements are highlighted in the introduction followed by the instrumentation, materials and methods. Various applications relating to enzyme activity measurements, clinical monitoring, process monitoring, multianalyte determination, hybrid sensing, environmental monitoring, non-aqueous measurements and other miscellaneous applications are described. A brief note on future developments and a detailed reference list is also included.

Investigation of catalytic properties of immobilized enzymes and cells by flow microcalorimetry

The investigation of catalytic properties of immobilized biocatalysts (IMB) is a time-consuming and not-always-simple procedure, requiring a simple and accurate method of enzyme-activity measurement. In comparison with generally-used techniques, flow microcalorimetry (FMC) has proven to be a very practical and versatile technique for direct monitoring of the course of enzyme reactions. The principal advantage of FMC is integration of the enzyme reaction and its monitoring in one step. This review summarizes the information needed for the complete kinetic or catalytic characterization of the IMB by FMC, without the requirement of any independent analytical method. The optimal experimental procedure is proposed. Examples of experimental studies on immobilized biocatalysts using the FMC are provided. The method is applicable to purified enzymes as well as to enzymes fixed in cells.

Thermal biosensors in biotechnology

The application of enzyme thermistor devices for the continuous monitoring of enzymatic processes is described. Different hardware concepts are presented and discussed, practical results are also given. These devices were used to analyze the enantiomeric excess in biotransformation processes and for thermal immunoanalysis. In addition, the biosensors were applied for the monitoring and control of an L-ornithine producing process and for the application in hemodialysis monitoring. A review section discusses the use of thermal biosensors for monitoring biotechnological processes in general.

Thermistor-based biosensing

In this review a universal thermistor-based biosensor system is described with examples from clinical chemistry, bioprocess monitoring and environmental control. The technique is based on the measurement of the small temperature changes associated with enzymatic reactions occurring in a microreactor with immobilized enzyme. The system has good operational stability and a sensitivity that permits measurements down to 1 microM concentrations. Current developments include devices constructed by micromachining for multisensing purposes and miniaturised instrumentation intended for use in portable monitoring. With use of special supports for enzyme immobilisation even untreated whole blood samples can be applied. Another current line of investigation involves hybrid biosensors, such as combinations of electrochemistry and calorimetry into bioelectrocalorimetric devices with interesting new properties.

Determination of minute amounts of ATP by flow injection analysis using enzyme amplification reactions and fluorescence detection

A flow-injection system for assay of trace levels of ATP is described that incorporates a small column reactor containing co-immobilized hexokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase. In the presence of appropriate cofactors, ATP is by the synergistic operation of the enzymes repeatedly recycled, resulting in substrate amplification. The ultimately generated NADH is measured fluorometrically. By this approach, where the enzymatic degradation step and the detection step are completely separated, it is possible to operate them individually under optimal conditions. The amplification factor is directly proportional to the residence time of the sample zone within the enzyme reactor, which time might be manipulated by altering the flow-rate and in the extreme by performing stopped-flow experiments. Amplification factors between 15 and 1000 were obtained, but it was found that increased amplifications did not lead to significantly lower detection limits; thus, it appears that a practical lower limit of detection is of the order of 1-5 nM. An investigation of this paradoxical feature, and a possible explanation for it, is given.

Enhancing biosensor performance using multienzyme systems

Enhancing the performance of biosensors, in terms of increasing the range of analytes that may be detected, and the sensitivity and specificity of the detection event, would improve the prospects for commercializing this technology. Coupling the catalytic activities of several enzymes is one approach being used to address these issues. Sequences of enzymes, where ligand binding triggers the activation of enzymes, or where biocatalytic pre-concentration of intermediates permits augmentation of the signal, may be used. In addition, enzymatic recycling of the analyte can be used to increase the sensitivity by several orders of magnitude.

An integrated silicon thermophile as biosensor for the thermal monitoring of glucose, urea and penicillin

A new kind of calorimetric biosensor for the measurement of the heat (molar enthalpy change) of enzymatic reactions is presented. The device operates according to the Seebeck effect, the same principle on which thermocouples are based. The thermopile used in this work consists of an array of p-type silicon/aluminium strips integrated on a thin silicon membrane (5 microns). Its sensitivity is about 1 V output voltage per watt of heating power, corresponding to a temperature resolution in the order of 10(-5) K and a heating power resolution of some tenths of a mu W in the flow system used. Furthermore, this performance is obtained without any control of external temperature because of the high common-mode thermal noise rejection ratio of the thermopile. The universal technique of calorimetry combined with the specificity of biochemical reactions makes this biosensor very versatile, with a broad range of possible applications. Glucose oxidase together with catalase for the determination of glucose, urease and penicillinase for the monitoring of urea and penicillin G, respectively, were immobilized directly onto the back side of the thermopile. The sensor was operated in conjunction with flow injection analysis which, in addition to its traditional advantages, allows preconditioning of the samples. Thus, artefacts due to mixing effects were suppressed and interference caused by differences in ionic strength between sample and carrier was strongly decreased. Detection limits between 1 and 2 mM were reported in the flow injection conditions described.

Enzyme assays

The past year or so has seen the development of new enzyme assays, as well as the improvement of existing ones. Assays are becoming more rapid and sensitive as a result of modifications such as amplification of the enzyme product(s). Recombinant DNA technology is now being recognized as a particularly useful tool in the search for improved assay systems.