Low-Melting Alloy Microfluidic Electrode Based on Hydrophobic Valve and its Application in Coulter Counter

This paper presents a new method to fabricate low-melting point alloy (LMPA) electrodes inside polydimethylsiloxane (PDMS) microfluidic channels. The melting alloy is injected into a subchannel designed as a hydrophobic valve, which provides a threshold pressure to flow through. Thus, with an appropriate control of the injecting pressure, the melting alloy can fully fill the subchannel without passing through it and blocking the main channel. After the solidification, an LMPA microelectrode is formed and automatically aligned on the side of main channel. A Coulter counter microfluidic chip is fabricated using this method and a coefficient variation (CV) of 1.99% is obtained for 10-μm beads. The results show that the proposed method is a feasible solution to fabricate robust microelectrodes in polymer-based microfluidic chips without the expensive lithography or sputtering.