Positively Charged Noble Metal Nanoparticles Colloid For SERS In Situ Detection Of Anions

With the development of scientific technology and economy, the human life has improved. Meanwhile, all sorts of security issues also follow. These issues were originated the misused of chemical substances. As an important sort of pollutants, the rapid detection method of anionic pollutants such as the explosives and toxic pollutants is urgent. Currently, the traditional methods of detection of these chemicals are commonly performed with complex instrumentation such as chromatography and mass spectrometry, which required the complex sample pretreatment process and the long detection period.Surface-enhanced Raman scattering (SERS) with the fine sensitivity, selectivity and fingerprint characteristics is a widely pursued spectroscopic tool in the analysis of chemical and biological samples. The key of application of surface enhanced Raman detection is preparation with high SERS activity of the substrate, which can make the analyte fully adsorbed onto the surface of the substrate. The most popular noble metal nanoparticle colloids are generally prepared by chemical reduction of an appropriate soluble metal salt, eg. silver and gold colloidal nanoparticles charge-stabilized by anions such as citrate and hydroxylamine with negatively charged nature, which can be usually employed to detect the compound with sulfur or nitrogen. For other pollutants, the surface modification of substrate is required. The detection is achieved by adsorbing the analyte in the hotspot using the interaction between modifier and analyte.In this dissertation, we developed a surface enhanced Raman spectroscopy in situ detection method based on electrostatic interactions. To achieve the surface enhanced Raman spectroscopy in situ detection of anions, the positively charged noble metal nanoparticles was obtained by surface modification. The main contents are as follows:(1) The silver nanoparticles colloid modified by cysteamine hydrochloride was the SERS substrate to detect the sodium pentachlorophenate on the surface fruit and vegetables in situ, an insecticide. The -NH3+ on the surface of silver nanoparticles is present by modification cysteamine hydrochloride, which can adsorbed the sodium pentachlorophenate by electrostatic interaction into the hotspots. The surface modification of silver nanoparticles sol can be applied to detect anionic contaminants on the surface of a fruit and vegetable in situ nondestructive by surface enhanced Raman spectroscopy, which has the potential applications in the fast food safety analysis.(2) The transformation of the negatively charged silver nanoparticles colloid into positively charged ones was demonstrated by sodium diethyldithiocarbamate (DDTC), a potent copper chelating agent. The positively charged silver nanoparticles colloid was applied in situ to detect the inorganic explosives anions NO3- and ClO4- on the surface with a portable Raman spectrometer through the electrostatic interaction. The common plasmonic metal nanomaterials could facilely be transformed into the positive-charged ones with DDTC surface modification, which could be contributed to the trace analysis of inorganic anion oxidizer in crime scene investigation and homeland security combining with a portable Raman spectrometer.