The response characteristics and ideal operating conditions are described for a novel fiber-optic internal enzyme biosensor for hydrogen peroxide. The sensing mechanism involves hydrogen peroxide entering an enzyme containing internal solution by crossing a gas-permeable membrane. Once in the internal solution, the enzyme horseradish peroxidase (HRP) catalyzes the chemiluminescent reaction between hydrogen peroxide and luminol. The resulting light intensity is monitored and related to the analyte concentration. Sensor response properties strongly depend on the composition of the internal enzyme solution. Specifically, the magnitude, rate, and stability of the sensor response depend on the pH, buffer salts, and the concentrations of luminol and horseradish peroxidase. Under optimal conditions, the steady-state signal is linearly related to the square of the hydrogen peroxide concentration according to the kinetics of the HRP catalyzed reaction.
The resulting hydrogen peroxide biosensor is used as the internal sensing element of a glucose biosensor by immobilizing glucose oxidase on the outer surface of the gas-permeable membrane. This glucose biosensor possesses a linear dynamic range from 2 to 18 mM with response times shorter than 60 s. Accurate measurements of glucose in blood are demonstrated.