Restrictive dual capacitively coupled contactless conductivity detection for microchip electrophoresis

Abstract

New capacitatively coupled contactless conductivity detection (C4D) for microchip electrophoresis with enhanced detection limit down to ppb level is developed. Our approach to improve sensitivity is to restrict the detection cell to enhance the signal coupling into the confined detection cell. A C4D cell design consists of a pair of dual top-bottom RF emitting electrodes and a pair of receiving electrodes disposed downstream onto a very thin plastic microfluidic chip. The dual C4D electrode geometry in conjunction with thin electrophoresis microchips doubles the total cell capacitance while electrodes are very close to the channel therefore reduce the cell impedance with enhanced signal coupling resulting to enhanced signal to noise ratio, improved sensitivity and enables a more efficient signal coupling and extraction from the detection volume in the electrophoretic microchip. A detection limit of 0.3 - 1 μM has been demonstrated with this optimized dual C4D detector. The average detector sensitivity obtained is 42 mV/mM.