INTRODUCTION Among the enzyme-based electrochemical biosensors (1-4) for the determination of clinicaland industrial analytes, the most widely used and studied are those for glucose. Because glucose oxidase transfers electrons to diffusing and nondif-fusing mediators, withstands chemical immobilization techniques, and has a high turnover rate (~ 103 s'1) at ambient temperature, this enzyme is commonly used in glucose sensors. Miniaturization of glucose sensors is relevant both to the measurement of glucose in small volumes and in vivo, and size is important in monitoring the dynamics of local chemical events in specific regions of an organ. Sensor miniaturization has allowed in vivo measurements of neurotransmitter release from dopaminergic neurons in mammalian brain tissue with microvoltammetric electrodes (5). In addition, microsensors with dimensions smaller than their substrate diffusion layer rapidly attain steady-state conditions via radial mass transport, allowing the use of signal-averaging techniques. Glucose microsensors have been made by using glucose oxidase immobilized on microcylinders, microdisks, and microplanar surfaces (6-17). These microsensors measure either the change in oxygen partial pressure (16), the concentration of evolved