Demonstrating Size and Charge Exclusion on SERS Substrates (original) (raw)

Abstract

Surface-Enhanced Raman Spectroscopy (SERS) amplifies Raman laser-stimulated emission of molecules when they are in close proximity to a metal surface, commonly silver, platinum, and gold. These amplifications are at least six orders of magnitude, thus providing the sensitivity to detect physiologically relevant concentrations of molecules in a biological sample. This enhancement is provided by chemical adsorption, which provides some selectivity due to the chemical bonds involved. In a biological sample, however, one may not be interested in the concentrations of all the molecules present. This problem can be addressed by using the concepts of size and charge exclusion in conjunction with a porous metal electrode acting as a SERS substrate. Size exclusion allows us to focus on receiving spectral information from only certain molecules by restricting the size of the pores present in our substrates. This method lets molecules under the pore diameter to be detected, while rejecting those that are larger than the diameter. Using this electrode, we present a charge to the previously neutral surface of the substrate, varying the charge to enable chemical species to adsorb and desorb at our prompting. Taking advantage of the chemistry of the different molecules present in the sample, we can select molecules for adsorption based on their particulary charge. Applying these concepts, we demonstrate quantitative analysis of several biological molecules typically present in a biological sample at physiological concentrations.

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