Plasmonic heating effect in SERS-based nanoplastic detection

As interest in nanoplastics (NPs) increases, various detection techniques have been suggested. Among them, surface-enhanced Raman spectroscopy (SERS) has received a lot of attention because it provides the information of molecular fingerprints with outstanding high sensitivity. On the other hand, it has been known in SERS community that the laser irradiation used in SERS measurement causes a plasmonic heating effect in the local hot spot area on the surface. However, such heating effect has not been considered together with the thermofluidic properties of nanoplastics during the measurements. Here, we systematically examined such heating effects on the SERS detection of NPs. We used standard type of polystyrene (PS) and poly (methyl methacrylate) (PMMA) nanoparticles, which are deposited on a well-controlled SERS surface. Dark field spectroscopy allows the optical visualization of individual particles, where laser was irradiated on with controlled power density. We showed that nanoplastics can be locally melted on the SERS surface with increasing laser power, verifying the permeation of nanoplastics into a hotspot. Our results suggest that when measuring nanoplastics by SERS, factors such as laser power, wavelength, substrate property and type of NP should be considered all together.