Coupled enzyme reactions in enzyme electrodes using sequence, amplification, competition, and antiinterference principles

Theoretical and Numerical Analysis of Nonlinear Processes in Amperometric Enzyme Electrodes with Cyclic Substrate Conversion

A theoretical model of amperometric enzyme electrodes has been developed in which chemical amplification occurs in a single enzyme membrane via cyclic substrate conversion. The system is based on non-stationary diffusion equations with a nonlinear factor related to the Michaelis–Menten kinetics of the enzymatic reaction. By solving the nonlinear equations using the AGM technique, simple analytical expressions of concentration substrate, product, and amperometric current response are derived. Further, biosensor sensitivity, resistance, and gain are obtained from the current. MATLAB programming was used to carry out the digital simulation. The analytical results are validated with the numerical results. The effect of substrate concentration, maximum enzymatic rate, and membrane thickness on biosensor response was evaluated.

Modelling amperometric enzyme electrode with substrate cyclic conversion

A mathematical model of amperometric enzyme electrodes in which chemical amplification by cyclic substrate conversion takes place in a single enzyme membrane has been developed. The model is based on non-stationary diffusion equations containing a non-linear term related to Michaelis-Menten kinetic of the enzymatic reaction. The digital simulation was carried out using the finite difference technique. The influence of the substrate concentration, the maximal enzymatic rate as well as the membrane thickness on the biosensor response was investigated. The numerical experiments demonstrate significant (up to dozens of times) gain in biosensor sensitivity at low concentrations of substrate when the biosensor response is under diffusion control.

A novel ISFET-type biosensor based on P450 monooxygenases

We made a biosensor based on ion-sensitive field effect transistor (ISFET) using P450 monooxygenase. ISFETs are electrical devices and have been used as pH sensors. We used genetically engineered P450 monooxygenase for our research because of its high enzymatic activity. The fusion enzyme between rat CYP1A1P450 monooxygenase and yeast NADPH-cytochrome P450 oxidoreductase was expressed in yeast Saccharomyces cerevisiae strain AH22. Yeast microsomal membranes were immobilized in an agarose layer on the ISFET. o-Deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin was catalyzed by the enzyme in the presence of nicotinamide adenine dinucleotide phosphate reduced form (NADPH). Formation of 7-hydroxycoumarin from 7-ethoxycoumarin was also measured by fluorescence. The difference of the voltage between the ISFET device and control device without enzymes showed a voltage increase along with the enzymatic reaction of P450 monooxygenases, and this voltage increase in the device was inhibited by addition of MnCl(2), an inhibitor of P450 monooxygenase. There was a positive correlation between the voltage increase in the ISFET device and the fluorescence intensity. This is the first electrochemical biosensing using P450 monooxygenases immobilized on the ISFET, and is applicable to the sensing of chlorophenol compounds.

Glucose determination by means of a new reactor/sensor system operating under non-isothermal conditions

The dynamic and steady-state responses as well as the response times of a glucose biosensor have been studied under isothermal and non-isothermal conditions as a function of analyte concentration. The presence of a temperature gradient across the catalytic membrane system improved the biosensor characteristics, because the dynamic and steady-state responses increased and the response times decreased under non-isothermal conditions. For example, a macroscopic temperature difference of 20 degrees C applied across the catalytic membrane system increases the biosensor sensitivity of 70% and reduces of 50% its response time. The dependence of the observed effects on the magnitude of the temperature difference applied has been correlated with the substrate (and products) transport across the catalytic membrane system due to the process of thermodialysis.

Enzymatic membranes for determination of some disaccharides by means of an oxygen electrode

Membranes for determination of maltose, lactose and sucrose with the use of an oxygen electrode are described. They were obtained by immobilization of glucose oxidase with suitable disaccharide hydrolase in gelatin or albumin. For the sucrose determination mutarotase was also used. The membranes contained one, two or three enzymes working in sequence. The enzyme composition of the membranes influenced the linear range slightly and the value of electrode response considerably. The electrode response of the maltose membranes was also affected by the immobilization material. The measurements with the use of enzymatic membranes were very sensitive to temperature and, to some degree, the pH of the sample. Stability of the membranes was differentiated. The albumin membranes for sucrose determination generated almost the same signal after 1 month of frequent use, whereas the gelatin membranes for lactose determination lost about 85% of the initial activity after 1 week of operation. The electrode response of both the gelatin and albumin maltose membranes decreased in the same time by about 50%.

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.