A Simple 3-D Microelectrode Fabrication Process and Its Application in Microfluidic Impedance Cytometry

Microfluidic impedance cytometry (MIC) has wide applications in single-cell analysis. However, the complex microelectrode fabrication process seriously restricts the miniaturization and commercialization of MIC devices. Common microelectrode configurations such as a coplanar electrode, a symmetric electrode, and a liquid electrode have difficulties in meeting the requirements of high detection accuracy and simple fabrication at the same time. Hence, a simple 3-D symmetric microelectrode fabrication process is developed in this article. We design a microchip containing both a microfluidic channel and a microelectrode channel. The alloy with high surface tension and low melting point is used to fabricate the 3-D microelectrodes by injecting the melted alloy into the microelectrode channel with a properly controlled driving pressure. The melted alloy flows into the microelectrode channel and automatically stops at the end of the microelectrode channel due to the effect of surface tension. This process intrinsically provides a high-precision alignment for the 3-D microelectrodes. The fabricated MIC chip is experimentally tested, and the results show that it can effectively count and classify microspheres of different sizes. This study can facilitate the development and commercialization of MIC devices.