The surface-enhanced Raman scattering detection of N-nitrosodimethylamine and N-nitrosodiethylamine via gold nanorod arrays with a chemical linkage of zwitterionic copolymer

Abstract

Due to the emerging issue of the contamination of sartan medicines and drinking water with N-nitrosodimethylamine (NDMA) and/or N-nitrosodiethylamine (NDEA), the detection of NDMA/NDEA has become an important theme. In this study, we utilized the focused ion beam (FIB) technique to fabricate gold nanorods (Au NRs) and Surface-enhanced Raman Scattering (SERS) substrates and modified them with 1,2-ethanedithiol to quench the high luminescence excitation background signals derived from the high density of localized surface plasmon resonance. To improve the surface hydrophilicity, zwitterionic copolymer PGMA-r-PSBMA was grafted onto the nanosurface of Au NRs, which was confirmed by contact angle analysis and AFM. Raman spectra of the copolymer were observed to confirm the successful grafting of Au NRs, which was also corroborated by TEM and SEM. The Au NRs could easily trap the small polar NDMA and NDEA molecules in aqueous solution due to strong zwitterionic hydrophilicity. Furthermore, the self-association of the anions and cations of the polymeric chain grafted in the hot spot zone assisted in trapping the NDMA/NDEA polar molecules. The Raman scattering cross-section of NDMA/NDEA molecules could be enhanced through the chemical linkage of 1,2-ethanedithiol and the self-association behavior of the zwitterionic copolymer. Accordingly, for the first time, we detected the characteristic peaks of NDMA/NDEA through SERS with detection limit of 10⁻⁸ M for both molecules.