Selective Labeling\nof Small Microplastics with SERS-Tags\nBased on Gold Nanostars: Method Optimization Using Polystyrene Beads\nand Application in Environmental Samples

Microplastics pollution is being unanimously recognized\nas a global\nconcern in all environments. Routine analysis protocols foresee that\nsamples, which are supposed to contain up to hundreds of microplastics,\nare eventually collected on nanoporous filters and inspected by microspectroscopy\ntechniques like micro-FTIR or micro-Raman. All particles, whether\nmade of plastic or not, must be inspected one by one to detect and\ncount microplastics. This makes it extremely time-consuming, especially\nwhen Raman is adopted, and indeed mandatory for the small microplastic\nfraction. Inspired by the principles of cell labeling, the present\nstudy represents the first report in which gold nanostars (AuNS) are\nfunctionalized to act as SERS-tags and used to selectively couple\nto microplastics. The intrinsic bright signals provided by the SERS-tags\nare used to run a quick scan over a wide filter area with roughly\n2 orders of magnitude shorter analysis time in respect of state of\nthe art in micro- and nanoplastics detection by μ-Raman. The\napplicability of the present protocol has been validated at the proof-of-concept\nlevel on both fabricated and real offshore marine samples. It is indeed\nworth mentioning that a SERS-based approach is herein successfully\napplied on filters and protocols routinely adopted in environmental\nmicroplastics monitoring, paving the way for future implementations\nand applications.