Microwave-plasma dry-etch for fabrication of conducting polymer microelectrodes

An inexpensive dry etch technology based on a low-pressure microwave plasma generated in a countertop microwave oven is characterized for the patterning of a conductive polymer microelectrode. The etch process is described, and the microwave-generated plasma is characterized by emission spectroscopy. The plasma is generated with an atmospheric mixture of mostly nitrogen and oxygen. A 10 μm wide band microelectrode composed of PEDOT:Tosylate, an optically transparent conductive polymer, is fabricated on a plastic substrate. Conductive polymer etch rates are approximately 280-300 nm/minute. A patterned microelectrode is characterized by atomic force microscopy. The horizontal distance of a 10-90% height of a plasma-etched 150 nm thick electrode was measured to be 360 ± 200 nm (n = 5). Electrodes are further characterized using steady-state cyclic voltammetry, and they have an electroactive area congruent with their geometric area. Finally, a complete device is assembled and used as a separation platform for biogenic amines. A microwave-etched 250 μm PEDOT:PSS electrode is employed for end-channel electrochemical detection on this microchip, where an electrophoretic separation of dopamine and catechol and a micellar electrokinetic chromatography separation of dopamine and serotonin are performed. Both mass and concentration LODs are comparable to other electrochemical detectors in an end-channel configuration. With the added advantages of easy processing, robustness, optical transparency, and low cost, we expect microwave-etched polymer films to be a viable alternative to traditional electrodes.