Optimized Pretreatment for Raman-Based Nanoplastics Detection

Nanoplastics are widely distributed in environmental and biological systems and are increasingly recognized as a potential ecological and health concern. Reliable analysis of nanoplastics in real environmental samples requires pretreatment; however, standardized and nondestructive pretreatment strategies remain limited. In this study, we develop a simple and efficient pretreatment protocol for Raman-based nanoplastic detection of polystyrene (PS) nanoplastics. Using PS nanospheres of three nominal sizes (300, 600, 800 nm) as a standard particle, four commonly applied chemical digestion reagents (H₂O₂, Fenton's reagent, NaOH, and HNO₃) were systematically evaluated. H₂O₂ effectively removed organic matter while inducing minimal alteration to polymer structure. For preconcentration, vacuum filtration combined with optimized ultrasonication achieved a recovery rate of up to 92% without causing membrane contamination. During sample preparation, freeze-drying suppressed the coffee-ring effect, and optimization of droplet volume enabled uniform particle deposition on the substrate, thereby ensuring reproducible single-particle Raman measurements. By optimizing digestion, preconcentration, and sample preparation steps, this pretreatment protocol reduces systematic biases introduced during sample preparation and provides a practical basis for standardized pretreatment of PS nanoplastics under the tested conditions.