Salt-Induced Nano-Trapping for Ultra- Sensitive SERS Detection of Nanoplastics in Drinking Water

The omnipresence of micro- and nanoplastics in the ecosystem and the health risks associated with these minute plastic particles has raised concerns worldwide. Whilst the detection and identification of microplastics has developed over the years, for nanoplastics this remains challenging due to limitations in analytical techniques used. Herein, the development of a simple and efficient method for the surface enhanced Raman spectroscopy (SERS) detection of nanoplastics through an ingenious use of colloidal gold nanoparticles (AuNPs) by as a SERS substrate is reported. A thorough investigation of the UV-vis spectra for the salt-induced aggregation of AuNPs was conducted to shift their maximum absorbance to the SERS excitation wavelength. Building upon these findings, the method combines salt-induced controlled heteroaggregation of nanoplastics and AuNPs with the filtration of the aggregated mixture to draw nanoplastics closer together, both placing them within the hotspot regions and increasing the number of heteroaggregated nanoplastics and AuNPs illuminated by the excitation source for SERS analysis. Consequently, the sensitivity for nanoplastics improves as does the noise (fluctuations) on the measured signal that is associated with the use of colloidal substrates. Using this method, an ultra-low concentration of 18.5 ng/mL of spherical polystyrene (PS) nanoplastics of 50 nm and 100 nm diameter in dH2O, respectively, was detected. Finally, the suitability of the methodology was successfully demonstrated for detecting nanoplastics in drinking water through recovery rates of 94.1% or higher.