Characterization of coatings on metallic nanoparticles by surface‐enhanced Raman scattering (SERS) for environmental purposes

Abstract

Abstract The increasing production and use of engineered inorganic nanoparticles (EINPs) escalate the risk for their unintended release into the environment. Coating of nanoparticles like natural organic matter (NOM) plays an important role in the stability, toxicity, and transport of nanoparticles. Surface‐enhanced Raman scattering (SERS) has been proven to be a promising method to detect and characterize the coating on noble metal nanoparticles. Here, we report on the synthesis of core‐shell Au–Ag nanoparticles (NPs) with a high SERS enhancement factor to study the exchange and competition of different coating agents with different binding abilities to simulate the release of NPs into a receiving environment with a number of potential coating agents. Suwannee River natural organic matter (SRNOM), 4‐mercaptobenzoic acid (4‐MBA), and 4‐mercaptopyridine (4‐MPy) were selected molecules for the experiments. The SERS experimental setup parameters such as aggregation size, laser excitation wavelength, and laser power were optimized before further experiments were conducted. It was shown that 4‐MPy has a higher binding affinity than SRNOM and 4‐MBA through the presence of simultaneous S and N atoms, which leads to dominating the coating process when two coating agents are present in the media at the same time. In addition, it was observed that 4‐MPy and 4‐MBA can replace the SRNOM coating on Au–Ag NPs.