Optimization of physical parameters of 'injected' metal electrodes for capacitively coupled contactless conductivity detection on poly(dimethylsiloxane) microchips

Capacitively coupled contactless conductivity detection (C⁴D) and its integration with Lab-on-a-Chip (LOC) systems has been well studied. However, most reported methods require multi-step electrode patterning/ fabrication processes which in turn leads to difficulty in consistently aligning detection electrodes. These limitations have the potential to compromise analytical performance of the electrodes and increase the time and cost of device production. We have previously demonstrated a simplified approach for C⁴D electrode integration with poly(dimethylsiloxane) electrophoresis LOC devices by utilizing 'injected' gallium electrodes. The developed fabrication process is fast, highly reproducible, and eliminates difficulties with electrode alignment. Using this approach C⁴D can be readily achieved in any microchip by simply adding extra 'electrode' channels to the microchip design. This design flexibility allows for straightforward optimization of electrode parameters. Here, we present the optimization of physical electrode parameters including orientation, length and distance from separation channel. The suitability of the optimized system for on-chip C ⁴D detection was demonstrated through the excellent intra- and inter-day repeatability (< 4 %RSD) of electrophoretically separated lithium, sodium and potassium ions.