Amperometric biosensor-based flow-through microdetector for microdialysis applications

A new flow-through electrochemical microcell was fabricated, in order to be used as an on-line detector in microdialysis-based investigations. The microcell is obtained by sandwich-like assembling the electrode system patterned on a glass chip and a silicon rubber gasket bearing the fluidic elements (inlet, outlet, flow channel, and containers for reference and counter electrode). Four Pt microelectrodes (100 (mu)m × 100 (mu)m squares), a Pt counter electrode, and a Ag reference electrode were patterned on a 9 mm × 14 mm glass chip by thin film technology. The silicon rubber cover was fabricated using a polydimethylsiloxane based precursor and a plastic mold, and it avoids significant dilution of the sample before getting in contact with the sensing electrodes. The microdetector can be directly connected to the outlet of the microdialysis probe reducing significantly the delay between sampling and detection. The microelectrodes were modified with enzymebased chemistries in order to detect glucose, glutamate, and choline by electrooxidation of the hydrogen peroxide produced in the reaction of the analytes with their corresponding oxidases. Problems concerning appropriate linear range, interference elimination, and cross-talk elimination were addressed.