Assessment of household settled dust via silicon nanomembrane analysis pipeline (SNAP)

Humans spend 70-90 % of their time indoors. However, there is a significant lack of knowledge regarding human exposure to microplastic particles and fibers (MPs) within the indoor environment. Fibers comprise more than 90 % of household settled dust worldwide and have been found in indoor air. Studies have identified MPs larger than 50 μm in indoor dust, but little information is available regarding smaller airborne or settled particles. We have developed methods to detect plastic particles that are larger than 10 μm in settled household dust by distinguishing plastic from cellulosic, proteinaceous, and inorganic particles using Nile Red to stain for plastics and Trypan Blue to stain for cellulosic materials while proteinaceous and inorganic materials remain unstained but visible via transmission light microscopy on ultrathin silicon nitride nanomembranes. This method, which we term the Silicon Nanomembrane Analysis Pipeline (SNAP), allows household settled dust and other sample types to be collected and analyzed on nanomembranes by multiple modes of metrology in situ, avoiding the need to transfer particles to different substrates for capture vs. analysis. Specifically, particles analyzed by fluorescence staining and optical imaging was followed by polymer identification via Raman spectroscopy and subsequently characterized via scanning electron microscopy for size and surface morphology. Using this innovative approach, microplastic particles larger than 10 μm in diameter have been identified in all settled dust samples.