Minimally invasive spatial and temporal concentration profiling within working glucose biosensors

The time-dependent evolution of analyte during the operation of working glucose biosensors has been profiled using a carbon fibre microelectrode (CFE). A simple procedure for the fabrication of minimally invasive CFE probes (<8 μm maximum diameter) is described. By positioning the CFE at well-defined distances from a working biosensor surface it has been possible to track the concentration of ferrocyanide, generated in the enzymatic assay for glucose, as a function of space and time. The results indicate that on the timescale of operation of typical glucose biosensors, the enzyme-mediated oxidation of glucose only occurs to a significant extent in a thin layer close to the sensor surface. In much of the analyte volume the reaction is negligible, contrary to present consensus.