A Micromachined Freestanding Electrochemical Sensor for Measuring Dissolved Oxygen

A freestanding, miniaturized electrochemical oxygen sensor for biomedical implantation has been microfabricated and characterized. The sensor is fabricated on a flexible and biocompatible polyimide substrate using lithographic techniques and singulated with an excimer laser. The sensor consists of a round-shaped planar sensing portion (diameter: 2.4 mm and thickness: 180 μm) and metal lines and contact pads for connection with external analytical tools. The sensing portion is comprised of three electrodes (working, counter, and reference electrodes), an electrolyte reservoir filled with liquid electrolyte, and a semipermeable membrane for oxygen introduction. The electrodes are patterned using a single layer of gold without the adhesion layer to eliminate any multilayer metallic structure in the sensing region. Both polydimethylsiloxane and fluorinated ethylene propylene semipermeable membranes are characterized. The fabricated sensor demonstrated an oxygen response of -14 nA/atm.% and good linearity (correlation coefficient exceeding 0.99). This device can potentially be incorporated into physiological applications, including monitoring oxygen tension in biomedical-related applications over semi-chronic time periods.