An apparent direct electron transfer between various electrode materials and peroxidases immobilized on the surface of the electrode has been reported in the last few years. An electrocatalytic reduction of hydrogen peroxide stars at about +600 mV versus a saturated calomel (reference) electrode (SCE) at neutral pH. The efficiency of the electrocatalytic current increases as the applied potential is made more negative and starts t o level off at about -200 mV versus SCE. Amperometric biosensors for hydrogen peroxide can be constructed with these types of peroxidase modified electrodes. By co-immobilizing a hydrogen peroxide-producing oxidase with the peroxidase, amperometric biosensors can be made that respond t o the substrate of the oxidase within a potential range essentially free of interfering electrochemical reactions. Examples of glucose, alcohol and amino acid sensors are shown.

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