The Preparation Of Silver Colloids And Their Application In SERS

The research on surface-enhanced Raman scattering (SERS) is one of the most popular research areas. Recently, the SERS spectroscopy has been applied to single-molecule detection, showing enhancement factor up to 1014～1015. However, its industrialization still has bottlenecks and difficulties until now, such as the poor consistency on the SERS substrates prepared, which leads to the poor reproducibility of experimental data. The main purpose of this paper is to explore new methods to obtain reproducible and highly pure silver colloids and discuss the impact of the reaction time, reactant concentration on silver colloids. At the same time, the effects of the reaction time, post-treatment and sample cells on SERS have been investigated. The main contents can be divided into the following sections:1) Silver colloids are prepared by the microwave-assisted reduction method with sodium citrate as a reducing agent. The characterizations of silver colloids are obtained by UV-visible absorption spectroscopy, transmission electron microscopy and atomic force microscopy. The results show that silver colloidal particles are spherical-like and the distribution is uniform. With the increasing of the reaction time, the size of silver colloidal particles gradually increases.2) The absorption peaks of silver colloids with the different concentrations of silver nitrate and sodium citrate are tested. When the concentration of sodium citrate is fixed, the absorption peak of silver particles undergoes red shift and then blue shift with the increasing of the concentration of silver nitrate, i.e. the size of particles first increases and then decreases; When the concentration of sodium citrate is increased, the absorption peak of silver colloidal particles exhibits blue shift and then red shift, i.e. the size of nanoparticles increases and then decreases.3) The SERS activities of silver colloids with Rhodamine 6G as a probe molecule are checked. The results present that the sizes of silver colloidal particles after the reaction time 3 minutes are between 50nm-60nm, and have the best Raman enhancement.4) The properties of silver colloids with the different post-treatment and its Raman enhancement effect are tested. With the same reaction time, the original silver colloids solution gives the weakest SERS signals. After centrifuging and washing twice, silver colloids have the strongest SERS signals, and the results are highly consistent. 5) The effects of the sample cell on the Raman enhancement are investigated. Experimental results give that the Raman signals for different locations are quite different. Under the same condition, the Raman signals of the sample measured in the capillary are compared with the strongest signals tested in the glass slide. It is shown that the Raman signal strength of the sample measured in the capillary is the higher than that of samples in the glass slide.