Precision flow focusing in 3D printed microchannels for enhanced impedance spectroscopy

Precise particle positioning is critical for achieving high-quality signal acquisition in impedance-based single-particle analysis. We present a novel microfluidic platform that enables tunable three-dimensional (3D) hydrodynamic focusing using a single-layer microchannel fabricated via projection micro stereolithography (P μ SL). The design integrates a nozzle structure, vertical sheath flow, and a constricted sensing region. Unlike planar designs where particles often settle on the channel bottom, the nozzle structure elevates the particle stream above the floor, minimizing particle–wall interactions. This configuration enables robust lateral and vertical confinement, with positioning governed by flow dynamics rather than particle size, leading to more consistent alignment near the electrodes. Numerical simulations and fluorescence imaging confirm precise control of particle trajectories within the channel cross-section. Impedance measurements using fluorescent microspheres demonstrate significant improvements in signal-to-noise ratio (SNR), reaching up to 17.38 dB. This scalable, label-free approach offers enhanced signal quality and fabrication simplicity, making it well-suited for integration into impedance-based biosensing, cytometry, and chemical detection systems. • Tuneable flow focussing helps to maximize impedance-based measurement sensitivity. • A high-resolution 3D P μ SL-printed micronozzle generates highly-focussed flow. • Single-step printed channel streamlines fabrication and enhances functionality.