Quantification of Nanoplastics and Inorganic Nanoparticles via Laser-Induced Breakdown Detection (LIBD)

Nanoparticles with diverse characteristics are difficult to quantify at low concentrations in the water environment (10⁶-10⁹ particles mL^-1 for nanoplastics originating from the breakdown of plastic debris) for the evaluation of effective treatment methods. This study examines the sensitivity, or limit of detection (LOD), of laser-induced breakdown detection (LIBD) for the counting of nanoparticles, including nanoplastics. For polystyrene (PS) standards with sizes of 20-400 nm, LIBD shows relatively low LODs (for example, 2 × 10⁶ particles mL^-1 for 100 nm particles) compared with turbidity monitoring, UV-vis spectroscopy (both 6 × 10⁸ particles mL^-1), and nanoparticle tracking analysis (2 × 10⁷ particles mL^-1). For nanoplastics (PS, polypropylene, and polyethylene terephthalate), the detection limits are 10⁴ - 10⁵ particles mL^-1, one to two orders of magnitude lower than the PS standards. LIBD can quantify inorganic nanoparticles, such as zeolite, titania, and hematite. The sensitivity increases (i.e., LOD reduces) with increasing particle density, while some particles are prone to artifacts. The low LODs make LIBD a robust technique for counting nanoparticles of various types and sizes, even at the concentrations found in the permeate of membrane-based water treatment systems. Given the high sensitivity, LIBD has the potential to be applied in membrane integrity monitoring and fundamental studies on membrane mechanisms.