Microfluidic thin-layer flow cell for conducting polymer growth and electroanalysis

Abstract

The design and fabrication of a low cost and versatile poly(dimethylsiloxane) (PDMS)-glass microchip configured to house an electrochemical thin-layer flow cell is reported. The microchip contains an integrated electrochemical cell comprising a sputtered channel gold working electrode (110μmx5mm) and a reference and auxiliary electrode housed together in the channel outlet. The facile fabrication method allows for the production of fully disposable, gasket-free thin-layer cells for a range of channel depths (35–180μm), that are suitable for low-cost, chip-based electroanalytical applications. The microchip was found to exhibit thin-layer behaviour during a series of voltammetric experiments conducted in ferrocyanide/ferricyanide. The cell was observed to experience a high resistance to current, which was dependent on the distance from the channel working electrode to the auxiliary electrode.Polyaniline (PANI) monoliths were grown electrochemically onto the channel electrode (5mm in length). The thickness of these monoliths was shown to be uniform along the length of the electrode. This demonstrates that the IR drop along the channel was not significant over this electrode length. The growth behaviour of the PANI on-chip was further examined in terms of channel depth and flow rate. It was observed that, under certain flow conditions, PANI monolith thicknesses were limited to approximately half the channel depth being employed. This was attributed to increasing volumetric flow rates during PANI growth. Increasing flow and hence convection rates were due to the displacing of channel volume during voltammetric electropolymerisation of PANI.The microfluidic electrochemical cell incorporating the PANI-modified channel electrode was then used for the amperometric detection of ascorbic acid. When the working channel electrode was placed closest to the channel outlet, the microchip was capable of the detection of ascorbic acid at a sensitivity of 15.7μAmM−1cm−1 which is greater than reported previously under similar conditions.