On-chip capacitively coupled contactless conductivity detection using "injected" metal electrodes.
We demonstrate the use of injected gallium electrodes for capacitively coupled contactless conductivity detection (C(4)D) within a microchip electrophoresis device. Evaluation of the electrodes for quantitative detection of electrophoretically separated lithium, sodium and potassium ions showed the system offers competitive detection limits of 6.1 × 10(-6) M, 6.7 × 10(-6) M and 8.5 × 10(-6) M, respectively. The fabrication process is fast, highly reproducible, and eliminates difficulties with electrode alignment. Using this approach C(4)D can be readily achieved in any microchip by simply adding extra 'electrode' channels to the microchip design.