Microfluidic chips for capillary electrophoresis with integrated electrodes for capacitively coupled conductivity detection based on printed circuit board technology

A simple and low budget microfabrication method compatible with mass production was developed for the integration of electrodes for capacitively coupled contactless conductivity detection (C4D) in Lab on a Chip devices. Electrodes were patterned on a printed circuit board using standard processing. This was followed by lamination–photolithography–lamination to cover the electrodes in dry film photoresist (DFR) using an office laminator. This resulted in a flush, smooth surface on top of the detection electrodes, enabling subsequent integration of a microfluidic network at a distance dictated by the thickness of the DFR (17 μm, 30 μm and 60 μm were used in this work). This process was applied to create two types of detectors, re-usable detectors to be used in combination with a separate microfluidic network and integrated detectors where the microfluidic network is irreversibly sealed to the detector. A poly(dimethylsiloxane) (PDMS) slab containing the microfluidic network was positioned on top of the re-usable detectors to create the PDMS hybrid devices. The integrated DFR devices were created by patterning and sealing the microchannel in DFR using subsequent lamination and lithographic steps. The sensitivity of the C4D made using this new technology for small inorganic cations was between 6 and 20 μM, which is comparable with devices made using significantly more advanced technologies. Where the 17 μm film slightly improved the sensitivity, the use of 30 μm thick insulating films was preferred as these did not impose significant restrictions on the applicable field strengths.