AMPEROMETRIC INTERNAL ENZYME GAS-SENSING PROBE FOR HYDROGEN-PEROXIDE

A novel sensor for the selective detection of hydrogen peroxide is described. This sensor is based on the internal enzyme concept configured in a gas-sensing arrangement. Hydrogen peroxide diffuses across a microporous PTFE membrane and enters the internal solution. The entering hydrogen peroxide is then electrochemically reduced by a horseradish peroxidase (HRP) catalyzed reaction with ferrocyanide as a mediator and the corresponding cathodic current is monitored. This sensing arrangement provides excellent selectivity over ionic species in solution that cannot penetrate the gas-permeable barrier. Critical design parameters include the ph and concentrations of electrolyte, HRP and ferrocyanide in the internal solution as well as the porosity and thickness of the gas-permeable membrane. The response properties are strongly influenced by temperature; where as, they are relatively insensitive to sample pH. The dynamic range for this sensor can be controlled by adjusting the composition of the internal solution, the physical properties of the membrane, and the temperature. The detection limit is 2 muM for sensors with an internal solution composed of 0.5 M potassium chloride, 0.05 M pH 7.4 phosphate buffer, 3 U ml-1 HRP and 0.5 mM ferrocyanide and a 0.45 mum microporous PTFE membrane. Sensors possess response times of 30 s and recovery times less than a minute.