Recessed microelectrode array for a micro flow-through system allowing on-line multianalyte determination in vivo

Using CMOS-compatible processes, a microelectrode system for use in a micro flow-through cell was manufactured. The electrode was specially designed t o enable multianalyte determination with immobilized oxidase enzymes and co mbines minimal flow dependency with a very small dead volume (< 1 mu L) of the cell. This allows biomedical applications like measurements of glucose and lactate in interstitial fluid, which can be collected by ultrafiltratio n. Besides a 3-electrode system with 4 individually addressable platinum wo rking electrodes, the sensor contains 2 electrodes that measure the conduct ivity of the sample as well as a Pt thermoresistor to measure the temperatu re. The temperature dependence in enzyme reactions can thus be controlled d uring on-line measurements. The 4 working electrodes comprise multielectrod e arrays, each comprising 192 micro-holes with a diameter of 3.6 mu m. They are arranged symmetrically around the central counter electrode, which is surrounded by a circular Ag/AgCl reference electrode. Between the array and the reference electrode are the loops of the Pt thermoresistor. The thermo resistor is electrically insulated from the measurement solution by a Si3N4 layer. A method for the pretreatment of platinum thin-film electrodes that increas es the reversibility of the electrode process is described. The chemical mo dification of the working electrodes by electropolymerization of a resorcin ol/1,3-diaminobenzene mixture enables interference-free measurement in bloo d and plasma as well as protection against electrode fouling.