Possibilities and Limitations of AFM-IR to Detect Nanoplastic Particles in the Atmosphere

Abstract

Potential impacts of nanoplastic particles (NPs) on human health through cellular uptake following inhalation have raised increasing concern. However, detection and quantification of atmospheric NPs remain challenging because most analytical methods lack either the spatial resolution or the chemical specificity needed to identify NPs in complex matrices. In this work, we investigate the possibilities and limitations of nanoscale infrared spectroscopy ena-bled by atomic force microscopy detection (AFM-IR) to identify NPs in ambient air. We establish an analytical framework that combines electrostatic precipitation, for representative nanoparticle col-lection on suitable substrates, with AFM-IR for chemical identification of individual particles at high spatial resolution. We achieved detection limits of 20 nm for silica and 80 nm for polystyrene nano-particles. Experiments conducted with synthetic aerosols confirm that NPs can be distinguished from major atmospheric particle types including soot, mineral dust and sulfate salts. Ambient aero-sol samples were dominated by sulfate, elemental and organic carbon with minor amounts of min-eral dust. Statistical considerations based on the absence of NPs in atmospheric samples suggest that NPs are several orders of magnitudes less abundant than other particles in ambient air. The AFM-IR method offers nanoscale chemical information of NPs, which will be essential for charac-terizing urgently needed nanoplastic reference materials. Although the method allows distinguishing between major particle types present of ambient aerosols and is specific enough to unambiguously identify NPs, the limited throughput of the method will require a selective enrichment of NPs to con-firm their presence in the atmosphere or in any other environmental compartment.