Microfluidic impedance cytometry chip combining composite cell pre-focusing microchannel and 3D symmetric microelectrodes for cell classification

Microfluidic impedance cytometry (MIC) enables label-free single-cell analysis; however, positional variations in particles within microchannels induce significant signal fluctuations, thereby limiting detection accuracy and reproducibility. This work presents a novel MIC chip that integrates a composite inertial-focusing microchannel with 3D symmetric low-melting-point alloy microelectrodes to achieve precise particle pre-focusing and stable impedance detection. Numerical simulations of secondary-flow fields and electric field distributions were systematically evaluated, confirming enhanced focusing performance and high signal uniformity. The MIC chips were fabricated using a single standard soft-lithography process combined with a reverse-extraction technique, significantly simplifying the fabrication processes while maintaining structural precision. Experimental results demonstrated a focusing efficiency exceeding 95%, a signal-to-noise ratio of 17.2 dB, and a low coefficient of variation of 7.9% for 15 μm particles, indicating significantly improved detection stability compared with conventional designs. Moreover, the proposed device enabled reliable classification of mixed particles and cells, highlighting its potential for high-accuracy, label-free cytometry and cell counting applications.