The plasmonic nanostructures required for the SERS are commonly in the form of solid substrates, or as colloidal solutions, both of them are not very useful to detect the biomarkers directly on human skins. Gel-based SERS substrates, into which the plasmonic nanostructures are incorporated, will be helpful for the direct collection of the biomarkers from secretions such as sweat. To elucidate these points, we studied the diffusion of Raman probe 4, 4’-Bipyridine (BPY) in the cetyltrimethylammonium bromide:sodium salicylate (CTAB:NaSal) gel. Au nano-island SERS chip was coated with a 1:1 complex of CTAB:NaSal . Then, the diffusion of the probe was studied by SERS spectra as a function of time. The SERS signal intensity increases gradually with increasing time. Highly porous gel rapidly absorbed aqueous analyte solutions generating large SERS signals. The subsequent increase in signal could arise from the diffusion of the analyte molecule into the gel and onto the Au aggregates. Importantly, this gel-based SERS sensor did not significantly compromise the SERS performance of the analyte. We propose that this gel-based SERS sensor can be smeared directly onto the skin surface to absorb the body fluids from sweat, enabling the detection of biomarkers.
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