Improving particle detection sensitivity of a microfluidic resistive pulse sensor by a novel electrokinetic flow focusing method

Abstract

A novel and simple method of improving the particle detection sensitivity of a microfluidic resistive pulse sensor was presented in this paper. This novel electrokinetic flow focusing method utilizes a focusing solution (with high resistivity) flowing from the upstream focusing channel to the downstream focusing channel. The focusing solution in the sensing gate works like a virtual insulation wall that greatly narrows the gate and thus improves the detection sensitivity. An equation was derived to relate the magnitude of the output signal to the resistivity and the width of the focusing solution. The width of the focused particle solution under different voltages was numerically predicted. The results show that the magnitude of output signal increases with the decrease in the width of the focused particle stream. More importantly, the detection sensitivity can be improved by decreasing the space occupied by the focusing solution in the upstream and downstream channels as much as possible. Detection of 1 μm particle with a sensing gate of 30 × 40 × 10 μm (width × length × height) was successfully achieved. The proposed method is simple and advantageous in detecting smaller particles without fabricating a small sensing gate.