Estimating the Analytical and Surface Enhancement Factors in Surface-Enhanced Raman Scattering (SERS): A Novel Physical Chemistry and Nanotechnology Laboratory Experiment

Abstract

R ecently, the National Science Foundation projected that the current 10-billion dollar nanotechnology sector will employ 2 million workers, including as many as 1 million workers in the United States. 1 It is expected that over 80% of the jobs created in this sector will require trained individuals in nanoscience. However, little training at the undergraduate level has been initiated to provide highly specialized scientists to this rapidly developing field. The proposed laboratory experiment, which was implemented for both undergraduate and graduate student laboratories in physical chemistry and nanotechnology, addresses the future projected demand.In 1998, G. C. Weaver and K. Norrod proposed an undergraduate laboratory to introduce the surface-enhanced Raman scattering (SERS) effect and to extend the scope of the Raman theory normally covered in physical chemistry courses. 2 A Raman-active molecule, pyridine, was adsorbed on colloidal silver nanoparticles (AgNPs) to demonstrate the large increase in Raman signal. Although successful, the SERS experiment did not estimate the analytical enhancement factor (AEF) and surface enhancement factor (SEF), the most important values for characterizing the SERS effect. 3,4 The Raman signal enhancement of 100À300 times was simply determined by calculating the ratio of integrated areas for specific vibrational modes of pyridine adsorbed on AgNPs and in solution. However, the pyridine concentrations (1.0 Â 10 À1 M for normal Raman and 6.25 Â 10 À3 M for SERS measurements) were extremely large when compared with the trace amounts of analyte that are now detected via SERS. In the following years, theoretical and experimental studies have demonstrated that single-molecule SERS-based detection and identification can be achieved under favorable circumstances. 5,6 Because of the enormous enhancement, SERS found numerous cutting-edge applications in medical, biological, chemical, military defense, homeland security, pharmacological, and environmental settings. 7À9 Most SERSbased detection and identification applications require an accurate determination of the magnitude of the signal enhancement.In this experiment, Raman and fluorescence spectrophotometers were employed to estimate the analytical and surface enhancement factors for rhodamine 6G adsorbed on a Creighton colloid. 10 Among the many kinds of SERS-active substrates, silver colloids are known to lead to huge enhancement factors and to enable single-molecule SERS experiments. 5À7,11 The Creighton method has been widely used for its simplicity, relative low cost, accessibility, and time efficiency. These parameters were critical in designing a feasible experiment for a laboratory. Not surprisingly, in 2007, Solomon et al. implemented the Creighton procedure for the synthesis of colloidal AgNPs as a new laboratory experiment for a general chemistry class. 12

Influence of natural organic matter on fate and transport of silver nanoparticles in saturated porous media: laboratory experiments and modeling

“…2a (I)) (Pavel et al 2012;Trefry et al 2010). The same modes were observed for the wet glass beads in the presence or absence of AgNPs ( Fig.…”

“…2b-d), which was also observed for other types of NOM or fluorescent dye molecules (Pavel et al 2012;Trefry et al 2010;Vogel et al 1999). Humic acid substances are known to exhibit a broad absorption in the visible spectral range (Vogel et al 1999).…”

Tangential Flow Ultrafiltration: A "Green" Method for the Size Selection and Concentration of Colloidal Silver Nanoparticles

“…23 2. Prepare 300 ml of a 2 mM NaBH 4 solution and 100 ml of a 1 mM AgNO 3 solution using autoclaved water cooled at 10 °C.…”

“…The final colloid had a characteristic golden yellow color ( Figure 1B). 22,23 The UV-Vis absorption spectrum of this colloid had a typical sharp, symmetrical surface plasmon peak (SPR) at 394 nm ( Figure 1C). The Raman spectrum of the original Creighton colloid and the final 100-kD retentate presented only three vibrational modes, namely the bending (1640 cm …”

“…First, unfuctionalized AgNPs (4 L, 15.2 μg ml -1 ) were synthesized using the well-established Creighton method 22,23 by the reduction of AgNO 3 with NaBH 4 . AgNP polydispersity was then minimized via a 3-step TFU using a 50-nm filter (460 cm 2 ) to remove AgNPs and AgNP-aggregates larger than 50 nm, followed by two 100-kD (200 cm 2 and 20 cm 2 ) filters to concentrate the AgNPs.…”