# Plasmonic Nanomaterials for Micro- and Nanoplastics Detection
## 4 SERS-Based MNPs Detection  
As mentioned earlier in the introduction, the detection of plastic particles in the nanometric and micrometric range is still challenging for most techniques, but it is also an urgent issue that needs to be resolved. SERS is a very sensitive technique with a great potential for the detection of trace analytes [62; 63]. In fact, the SERS technique enhances the weak Raman signals of theprobe molecules thanks to the hot spot generated from a nano-metallic substrate at close distance [64]. At the same time, the SERS sensor can also identify chemical and biological species of different natures thanks to their diagnostic Raman fingerprints [65; 66]. SERS can thus provide qualitative and quantitative information that are useful for detecting the presence of MNPs in real samples, and even for discriminating between the different polymeric materials, by analyzing their different Raman signatures in the spectrum. The typical Raman active peaks mode for common plastic materials (i.e., polystyrene--PS, polymethyl-methacrylate--PMMA, polyethylene terephthalate--PET, polycarbonate--PC, polypropylene--PP, polyvinyl chloride--PVC) are reported in Table 2, together with their assignment. The most relevant and diagnostic peaks for each material are highlighted in bold in the table. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Polymer**} & **Wavenumber** & **Assignment** \\  & **(cm\({}^{-1}\))** & **(cm\({}^{-1}\))** \\ \hline  & 616 & In-plane aromatic ring deformation \\  & 795 & -C–H out-of-plane deformation \\  & **1003** & **Aromatic ring C–C stretching mode** \\  & **1030** & **C–H in-plane deformation** \\  & 1150 & C–C stretching mode \\  & 1205 & C\({}_{6}\)H\({}_{5}\)–C vibration \\ PS & 1310 & CH\({}_{2}\) in-phase twist \\
[67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80] & 1352 & CH deformation \\  & 1410 & Ring stretching \\  & 1455 & CH\({}_{2}\) bending \\  & 1527 & Ring stretching \\  & 1583 & C–C stretching \\  & 1600 & Ring skeleton stretching \\  & 2915 & Asymmetric CH\({}_{2}\) stretching \\  & 3060 & Aromatic CH stretching \\ \hline  & 602 & C–COO stretching, C–C symmetric stretching \\  & **817** & **C–O–C symmetric stretching** \\  & 878 & CH\({}_{2}\) stretching \\  & 925 & CH\({}_{2}\) stretching \\  & 1000 & O–CH\({}_{3}\) rock \\ PMMA & 1081 & Stretching C–C skeletal mode \\
[67; 68; 74; 78; 81; 88; 89; 90; 91; 92; 93] & 1264 & C–O stretching, C–COO stretching \\  & 1648 & C–H asymmetric bending of \(\alpha\)–CH\({}_{3}\) and C–H asymmetric \\  & 1460 & bending of O–CH\({}_{3}\) \\  & 1648 & Combination band involving C–C stretching \\  & **1736** & **C=O stretching of C-COO** \\  & 2848 & Combination band involving O–CH\({}_{3}\) \\  & **2957** & **C-H stretching of O–CH\({}_{3}\), C–H asymmetric stretching** \\  & **ofa-CH\({}_{3}\) and asymmetric stretching of CH\({}_{2}\)** \\  & 3002 & C–H asymmetric stretching of O–CH\({}_{3}\) and C–H asymmetric \\  & 3454 & Overtone of 1736 cm\({}^{-1}\) \\ \hline  & 633 & C–C symmetrical bending vibration of the benzene ring \\  & **854** & **C=C stretching vibration between the benzene ring and the carboxyl group** \\  & 1116 & Ester C(O)–O and ethylene glycol C–C bonds \\  & 1178 & Ring in-plane C–H bond and C–C stretching \\ PET & 1288 & C(O)–O stretching \\
[74; 84; 94; 95] & 1308 & Ring C–H in-plane bending \\  & 1414 & C–H bending and O–C–H bending \\  & 1452 & CH\({}_{2}\) bending and O–C–H bending \\  & **1613** & **C=C stretching vibration of the carboxyl group** \\  & 1724 & C=O stretching vibration \\  & 2895 & C–H bond of methylene sequences \\  & 2960 & Methylene groups nearby oxygen atoms \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Typical Raman peaks of the different microplastics. PS: polystyrene. PMMA: polymethyl-methacrylate. PET: polyethylene terephthalate. PC: polycarbonate. PP: polypropylene. PVC: polyvinyl chloride. The most relevant modes are reported in bold.