Novel colorimetric detection of polypropylene nanoplastic via inhibition of salt-induced aggregation of gold nanoparticle

Colorimetric sensing using nanomaterials is widely studied, yet its application to nanoplastic detection remains underdeveloped. In this study, a non-destructive colorimetric method was developed to detect polypropylene nanoplastic (nano-PP) by inhibiting salt-induced aggregation of gold nanoparticles (AuNP). The method utilizes the electrostatic and steric stabilization effects of nano-PP to prevent aggregation triggered by NaCl (0.05–0.10 M), resulting in a quantifiable change in the localized surface plasmon resonance (LSPR) at 520 nm. Without nano-PP, rapid AuNP aggregation caused a red-to-gray color transition and LSPR signal loss. In contrast, increasing nano-PP concentrations effectively restored dispersion and recovered the 520 nm peak. Zeta potential analysis revealed a shift in nano-PP surface charge from –45.97 mV to + 39.27 mV, enabling electrostatic interaction with negatively charged AuNP. Control experiments using stabilizing agent or toluene alone failed to inhibit aggregation, confirming that stabilization occurred specifically in the presence of nano-PP. The detection limit ranged from 0.15 to 1.26 mL (9.95–51.08 mg/L), depending on NaCl concentration, with full detection achieved in 1 min. This technique offers a rapid, sensitive, and cost-effective alternative to conventional spectroscopic methods and establishes a foundation for extending colorimetric sensing to other nanoplastics in aqueous environments.