A Highly Sensitive SERS Substrate for Detection of Nanoplastics in Water

Raman spectrocopsopy is a technique which measures the unique Raman vibrations of analytes allowing for the acquisition of unique spectral fingerprints. However, due to the low strength of Raman scattering the sensitivity is poor. Surface-enhanced Raman scattering (SERS) takes advantage of the electromagnetic and chemical interaction between a target molecule and a rough metallic surface to enhance Raman scattering. This enhancement results in low sensitivity making SERS a powerful tool for detection purposes in various fields such as food safety, medicine, security, and environmental monitoring [1-3]. The enhancement of Raman signals is primarily attributed to the localized surface plasmon resonances (LSPRs) that occur on the surfaces of metallic nanostructures [4]. However, the degree of enhancement is strongly dependent on the chemical properties, size, shape, and interparticle gap of the metallic nanostructures that are inherent to the SERS substrate. Consequently, conventional techniques used for fabricating SERS substrate are typically expensive and require a high degree of precision [5]. To date, various methods have been utilized to fabricate effective SERS substrates for the detection of trace amounts of analytes. However, the free diffusion of molecules in fluids often results in a significant proportion of analytes not being able to effectively access the active regions (i.e. hotspots) of the SERS substrate in such samples, limiting the potential enhancement of Raman signals. The efficient attraction of a target analyte to the active regions of the substrate is therefore a crucial factor in maximising the sensitivity of SERS detection [6]. To this end, various hydrophobic SERS substrates have been realised as their greater contact angles for water-based analytes maximise the proximity of analyte molecules to the desired hotspots for sensitivities and specificities that allow the detection of analytes present in trace quantities [7].