Micro-3D-printed integrated system with liquid-metal coils for simultaneous size-selective sampling and concentration sensing of respirable ferrous metal aerosols

Respirable ferrous metal aerosols generated during metal processing and transportation pose exposure risks, motivating compact systems that can simultaneously classify particles by size and assess ferrous-particle concentrations. Conventional inductive sensors typically employ relatively large wire-wound coils and sensing channels, limiting their responses to few-micrometer particles. Here, we present a micro-3D-printed sampling-to-sensing platform integrating a two-stage inertial impactor, aqueous particle-transfer pathways, 100 μm sensing channels, and embedded liquid-metal coils within a monolithic polymer body. Vacuum-filled eutectic gallium-indium forms five-layer, 50-turn solenoids surrounding the sensing channels. The impactor stages exhibited aerodynamic cut-off diameters of 5.28 and 0.99 μm, enabling nominal >5 μm and 1-5 μm collection fractions. The coil achieved an inductance of 907.1 nH and a maximum Q-factor of 9.1 at 30 MHz. Under Fe-only aerosol conditions, peak-rate calibrations yielded R² values of 0.900 and 0.910, with time-resolved concentration-estimation nRMSE values of 6.72% and 8.95% for the two fractions, respectively. Under a controlled Arizona test dust background, inductive peak rates increased with Fe-source-associated increments in APS-measured total particle concentrations (R² = 0.9428 and 0.9348). Detectable responses persisted during a separate 60-min continuous mixed-aerosol challenge. These results demonstrate size-selective inductive sensing with initial evidence of concentration-dependent responses and operational stability under a laboratory-generated mineral-dust background.