Initial studies of a new approach to the design and use of enzyme-based reactor/sensor systems: amperometric system for glucose.
This paper describes the development and evaluation of a new approach to the design and use of enzyme-based reactor/sensor systems (so-called "enzyme electrodes"). In the new approach, the reactor/sensor design is such that the measured response corresponds to reaction of all substrate in a fixed volume of solution. The result is that equilibrium-based measurements can be made, which in turn should result in advantages such as extended linear ranges and reduced dependencies on experimental variables such as enzyme activity, temperature, activators, inhibitors, etc. The concept was implemented with a glucose oxidase/electron-mediator reactor system immobilized on a glassy-carbon electrode operated in an amperometric mode. The reactor/sensor system was used in a thin-layer (14 microns) cell such that the mean diffusion time of substrate (glucose) across the cell was very short (< 1 s) and the rate-limiting process was the chemical reaction at the reactor surface. In this way, it was possible to quantify the electrical charge corresponding to reaction of all the substrate in a fixed volume of solution perpendicular to the plane of the reactor system. Because the determined charge is dependent only on the total amount of substrate in the fixed volume, results exhibit linear range up to at least 2-fold the Michaelis constant and reduced dependency on pH relative to results obtained with steady-state responses from the same experimental system. A mathematical treatment is presented which yields equations that are consistent with time-dependent responses for current and charge and which provide a rational basis for several data-processing options evaluated.