Modeling of capacitively coupled contactless conductivity detection on microfluidic chips

Abstract

A novel equivalent circuit model of capacitively coupled contactless conductivity detection (C4D) on microfluidic chips is presented. The impedance of the solution in microchannels facing the two electrodes for C4D was first introduced in the model of C4D on microfluidic chips. The electrodes and the solution facing electrodes were divided into individual segments in the model, and the effect of the length of divided segments on the model was studied. A back-calculating method was put forward to calculate the stray capacitance between the electrodes, and the variation between the calculated value and the simulated value was only 6 %. To evaluate the accuracy of the model, a hybrid poly (methyl methacrylate) (PMMA)/polydimethylsiloxane (PDMS) microchip was fabricated and a simple model was built. Compared with the outputs of the simple model, the data predicted by the novel model show a much closer fit to experimental results, and the variations were within 8 % over a wide concentration range of 1–500 μm for potassium chloride.