A cyclo olefinpolymer microfluidic chip with integrated gold microelectrodes for aqueous and non-aqueous electrochemistry

Abstract

This paper presents an entirely polymeric microfluidic system, made of cyclo olefin polymer (COP), with integrated gold microband electrodes for electrochemical applications in organic media. In the present work, we take advantage of the COP's high chemical stability to polar organic solvents in two different ways: (i) to fabricate gold microelectrodes using COP as a substrate by standard lithographic and lift-off techniques; and (ii) to perform electrochemical experiments in organic media. In particular, fourteen parallel gold microelectrodes with a width of 14 μm and separated from their closest neighbour by 16 μm were fabricated by lithographic and lift-off techniques on a 188 μm thick COP sheet. A closed channel configuration was obtained by pressure-assisted thermal bonding between the COP sheet containing the microelectrodes and a microstructured COP sheet, where a 3 cm long, 50 μm wide and 24 μm deep channel was fabricated via hot embossing. Cyclic voltammetric measurements were carried out in aqueous and organic media, using a solution consisting of 5 mM ferrocyanide/ferricyanide in 0.5 M KNO₃ and 5 mM ferrocene in 0.1 M TBAP/acetonitrile, respectively. Experimental currents obtained for different flow rates ranging from 1 to 10 μL min⁻¹ were compared to the theoretical steady state currents calculated by the Levich equation for a band electrode (R. G. Compton, A. C. Fisher, R. G. Wellington, P. J. Dobson and P. A. Leigh, J. Phys. Chem., 1993, 97, 10410–10415). In both cases, the difference between the experimental and the predicted data is less than 5%, thus validating the behaviour of the fabricated device. This result opens the possibility to use a microfluidic system made entirely from COP with integrated microband electrodes in organic electroanalysis and in electrosynthesis.