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Size- and matrix-independent SERS quantification of polystyrene nanoplastics using interfacially assembled AgNPs@CTAB films
Summary
Researchers fabricated a two-phase interfacially assembled silver nanoparticle SERS substrate that quantifies polystyrene nanoplastics across the 29–100 nm size range without size-dependent bias, achieving detection limits as low as 0.049 µg/mL with strong reproducibility across tap, river, drinking, and seawater matrices.
Reliable quantification of nanoplastics (NPLs) in aquatic environments remains challenging due to their small size and limited hotspot accessibility in conventional SERS systems. Herein, a facile two-phase interfacial assembly strategy was developed to fabricate a uniform and reproducible surface-enhanced Raman scattering (SERS) substrate composed of silver nanoparticle (AgNPs) and cetyltrimethylammonium bromide (AgNPs@CTAB) at the toluene–water interface, which was subsequently applied for the detection of polystyrene nanoplastics (PSNPLs) with particle sizes of 29, 40, 65, and 100 nm. The optimized synthesis conditions (AgNO3:NaBH4 = 0.01:0.005 M and CTAB = 1 ppm) produced densely packed and interconnected AgNP networks that generated abundant plasmonic hotspots, enabling strong SERS enhancement of deposited PSNPLs. Toluene acts as a good solvent for PSNPLs at the interface, inducing surface softening and interfacial redistribution of PSNPLs, which reduces size-dependent hotspot accessibility and promotes uniform polymer–metal coupling. As a result, the method achieved size-independent quantitative analysis across 29–100 nm, demonstrating reliable reproducibility and ultrasensitive detection with limits of detection down to 0.049–0.111 µg.mL–1 and strong linearity (R2 > 0.98) across the concentration range of 0.5–2.5 µg.mL–1. The intensity of the characteristic PSNPL band at 1002 cm–1 remained stable in the presence of most interferents, with only minor signal enhancement observed for sugars, and maintained robustness across real-water matrices (i.e., tap, river, drinking, seawater, and artificial seawater). FE-SEM and optical microscopy (OM) analyses confirmed the formation of a continuous, interconnected AgNP network and the spatial distribution of PSNPL deposits as discrete domains across the substrate, supporting the structural uniformity and measurement reproducibility of the SERS platform. This reproducible and size-independent SERS platform enables rapid quantification of PSNPLs under diverse matrix conditions, representing a step toward practical environmental monitoring.