From automated Raman to cost-effective nanoparticle-on-film (NPoF) SERS spectroscopy: a combined approach for assessing micro- and nanoplastics released into the oral cavity from chewing gum

Microplastics (MPs) and Nanoplastics (NPs), a burgeoning health hazard, often go unnoticed due to suboptimal analytical tools, making their way inside our bodies through various means. Surface Enhanced Raman Spectroscopy (SERS), although is utilized in detecting NPs, challenges arise at low concentrations due to their low Raman cross section and inability to situate within hotspots owing to their ubiquitous size and shape. This study presents an innovative and cost-effective approach employing household metallic foils (aluminium and copper) as nanoparticle-on-film (NPoF) substrates for targeting such analytes. Leveraging from the near field enhancements due to plasmonic coupling amidst third-generation hotspots (TGHs) and second-generation hotspots (SGHs), the enhanced SERS activity is achieved. Furthermore, following an extensive comparison of the substrates' flexibility, sensitivity, reproducibility, and robustness, the copper foil-based NPoF platform was used to detect 100 nm polystyrene plastics down to 1 μg/ml concentration. Subsequently, a systematic detection of more than 250,000 MPs with automated Raman spectroscopy was performed, followed by the detection of NPs using SERS with a NPoF substrate in saliva samples released from the gum base in the oral cavity during a one-hour chewing activity. Overall, we report a cost-effective and versatile NPoF substrate, having the potential to screen a diverse array of environmental pollutants envisioned as a potential point-of-site tool by coupling it with a handheld Raman instrument.