Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 29: Poster: Experimental Techniques

MO 29.2: Poster

Thursday, March 11, 2010, 16:00–18:30, Lichthof

Peculiar Concentration Dependent Surface Enhanced Raman Scattering (SERS) of Glycine — •Animesh Ojha, Patrice Donfack, and Arnulf Materny — Jacobs University Bremen, Germany

Critical SERS behaviors, strongly influenced by the molecular density at the metal surface, are predicted for multipolar charged molecules. We present the case of glycine, a biological molecule coexisting in solution with its zwitterionic form having two oppositely charged chemical groups. SERS spectra of glycine have been recorded at different concentrations, from 1M, through 6.25x10.2M down to 1.95x10.3M (twice diluted each time) using silver nanoparticle colloids (AgNPs). The UV-visible spectra of pure AgNPs and of the mixtures with glycine at different concentrations, have been measured to explore the interaction behavior of glycine with AgNPs, and revealed an interesting observation indicated by the appearance, shifting, and strength of an additional absorption band as a function of the concentration. Moreover, the intensity of some SERS bands increases consistently with decreasing glycine concentrations and reaches an optimal value at a critical point of ≈ 6.25x10.2M. A further decrease in glycine concentration below the critical point causes the intensity of all SERS bands to drastically drop as expected. Besides the permanent chemisorption at all concentrations, the observed concentration dependent variation of SERS of glycine may be attributed to the specific nature of its interaction with AgNPs, such as molecular tails reorganization at the AgNPs surface as a function of density, which is further indicated by the changes in the UV-visible features of AgNPs with glycine.