Estimating the analytical and surface enhancement factors in SERS: A novel physical chemistry and nanotechnology laboratory experiment

Abstract

<p>A unique laboratory experiment was successfully implemented for undergraduate and graduate students in physical chemistry and nanotechnology. The objective of the experiment was to determine the SERS-based sensing capabilities of colloidal silver nanoparticles (AgNPs). These were quantified by estimating the most important values for characterizing the surface-enhanced Raman scattering (SERS) effect, the analytical (AEF) and surface (SEF) enhancement factors. SERS is an embodiment of Raman spectroscopy that currently finds many innovative applications (e.g. cellular imaging, chemical and biological warfare agent detection, protein and DNA recognition, and quality control in both the chemical and pharmaceutical industries). Students achieved this by synthesizing a Creighton colloid and characterizing its optical properties by UV-VIS absorption spectrophotometry. The AEF (7.4 x 104) and SEF (5.2 x 101) values were then estimated from the measured Raman, SERS, and fluorescence emission spectra of a test probe, rhodamine 6G (R6G), adsorbed on the colloidal AgNPs. The estimated enhancements did not correspond to single-molecule detection (maximum 105 and 7 x 109 for colloids). However, the R6G analyte concentration (1.0 x 10-6 M) was three orders of magnitude less than in previous laboratory experiments and facilitated rapid acquisition of SERS spectra with very good signal-to-noise ratio for the demonstrative calculation of the SERS enhancement factors. This laboratory experiment introduced students to the fundamentals of SERS spectroscopy and to the concepts related to the light scattering, surface chemistry and resonance effects. Furthermore, students acquired new instrumental and nanotechnology-related skills that will assist them in technologically-demanding careers.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>