Airborne micro- and nanoplastics revealed at the submicron scale using an optimized Nile Red-confocal microscopy...

Airborne micro- and nanoplastics (MnPs) are emerging atmospheric contaminants of increasing concern for inhalation exposure. However, their environmental quantification remains highly uncertain due to limited detection capability in the submicron range and insufficient validation of fluorescence selectivity. Here, we developed and validated an optimized Nile Red-assisted confocal laser scanning microscopy (NR-CLSM) workflow enabling direct on-filter detection of airborne MnPs down to 0.3 μm. An optimized excitation-emission configuration (561/570-670 nm) significantly enhances particle recovery while maintaining high polymer selectivity. Common nonpolymeric particulates, including mineral particles, activated carbon, and plant-derived debris, exhibit negligible fluorescence interference under the optimized conditions. Application to total suspended particulate samples collected in suburban Vietnam revealed MnPs concentrations ranging from 1.2 × 10⁴ to 2.5 × 10⁴ particles Nm⁻³ , with submicron and fine particles (0.3-2.5 μm) constituting the dominant fraction. Comparative imaging further demonstrated that non-optimized fluorescence configuration can substantially underestimate airborne MnPs abundance, particularly in the submicron size range. Optical validation using point spread function and full width at half maximum analysis confirmed that the observed submicron fluorescence signals correspond to discrete plastic particles rather than background artifacts. By reducing analytical bias and improving detection reliability, this validated NR-CLSM workflow provides a robust foundation for standardized monitoring and more accurate assessment of inhalation exposure to airborne plastic contaminants.