Aerosol Capture for Coupling to Microfluidics: A Miniaturized Low-Cost Device for Size-Resolved Particle Collection

Inhaled aerosols impact human health by depositing harmful species in the lungs (e.g., metals and organic pollutants) and act as a key pathway for airborne disease transmission. Aerosol inhalation is highly size-dependent, with smaller particles (particulate matter <2.5 μm, PM_2.5) depositing deeper in the lungs (e.g., alveoli) leading to strong correlations between PM_2.5 and mortality, along with other respiratory and cardiovascular diseases. A longstanding challenge for detailed aerosol chemical analysis is that most PM_2.5 health studies collect offline samples, which are subsequently analyzed offsite, requiring high-cost collectors and significant downstream effort and cost. Herein, we present a low-cost, miniature 3D-printed impactor coupled to a microfluidic channel to allow for downstream analysis of PM in liquid. After size-segregated collection of airborne particles within the device, water is flowed through a microfluidic channel that resuspends insoluble particles or dissolves soluble particles. Size-dependent collection efficiencies (50% cutoff diameters, <i>d</i>₅₀'s) for the supermicron (PM_>1) impactor were 0.8 and 1.0 μm using monodisperse (polystyrene latex spheres) and polydisperse (red-fluorescent spheres) standards, respectively. Coarse (PM_>2.5) impactor <i>d</i>₅₀'s were 2.4 and 2.6 μm, respectively. Optical photothermal infrared (O-PTIR) and Raman microspectroscopy confirmed collected particle composition. The sizes of re-entrained PSLs (1, 1.25, and 1.5 μm) were measured to have diameters of 1.0, 1.2, and 1.5 μm, respectively, with a Coulter Counter, indicating the successful downstream analysis of collected particles without modification during impaction and resuspension. Soluble particles (ammonium sulfate) were dissolved by the flowing water and measured with ion chromatography. This study shows that 3D-printed impactors are capable of collecting particles with a well-defined size cut, as well as nondestructively resuspending and chemically analyzing the particles. These 3D-printed devices are a miniaturized, low-cost (<$2) option that sets the stage for semicontinuous microfluidic analysis of size-selected aerosols to evaluate health impacts ranging from toxin exposure to disease transmission.