A novel silver solution for surface-enhanced Raman spectroscopy.

摘要

In order to search for possible applications of Raman spectra in biotechnology and pharmaceutical industry, a novel silver solution has been prepared, through the reduction of silver nitrate by hydrogen peroxide under mild pH condition, and developed to take advantage of the surface-enhanced Raman spectroscopy (SERS) effect for trace analysis of biological materials.; The preparation process has been optimized on time, temperature, pH, oxygen and reagents. At last a colorless, SERS active silver solution with a shelf life of more than 400 days could be reproduced. No ions other than silver and nitrate exist in the silver solution due to the fact that oxygen and water are the only byproducts of the reaction. Even after the exposure of the solution in strong UV light for more than 720 minutes, no major change of the UV-visible spectrum and the SER behavior could be noticed. By using benzoic acid as a model chemical, the excitation profile has been obtained and evaluated. The statistical results of TEM photographs show that the silver particles have almost a spherical shape with a mean diameter of 5 nm. Both reducing agents and oxidizing agents have significant effects on the SERS activities of the silver solution.; SERS of more than 20 chemicals, including dyes, organic acids, nitrogen compounds and antioxidants, have been collected using the silver solution along with two other well-known silver sols, Lee-Meisel and Creighton. The effect of pH on SERS, especially on those of organic acids, has been investigated. Special attention has also been paid to the study the effect of chloride ion on the SERS. Several biologically important chemicals, like 4-aminobenzoic acid, glutamic acid and 4-amino butyric acid, have been chosen to be the target chemicals for above research.; A practical application of normal Raman and SERS in industry has been investigated. 2-ethylhexyl-p-methoxycinnamate (EHMC), which is one of most widely used sunscreen agents in suncare products in the US, exhibits a strong Raman signal in both ethanol solutions of EHMC as well as in commercial sunscreen lotions containing this sun screen agent. A method for the direct detection and analysis of EHMC has been developed using Raman spectroscopy. This was accomplished by correlating the Raman intensities with the HPLC assays for a series of prototype suncare formulations. With the help of an optical fiber, it would be possible to employ Raman spectroscopy as an in-process method in the commercial production of suncare products containing EHMC.