Design considerations for SERS detection in colloidal solution: Reduce spectral intensity fluctuation

The intensity fluctuation of surface-enhanced Raman scattering (SERS) has seriously hampered its practical applications. The previous studies that involved SERS intensity fluctuation mostly focus on the assembled substrates or single molecule and single nanoparticle but have few attention on colloidal solutions containing numerous molecules and/or nanoparticles. Here, we studied the time-elapsed SERS spectra of three different analytes in colloidal solution. Their peak intensities fluctuated simultaneously and uniformly throughout the acquisition process and had no correlation with their wavenumber wandering. Gravity-induced inhomogeneous distributions of Ag nanocubes in solution led to the spatial and temporal variations of peak intensities, which could be reduced by altering the integration time, particle concentration, and solvent viscosity and density. Furthermore, the dissimilar interactions between analytes and Ag nanocubes showed non-detectable influence over their intensity fluctuations. This investigation gives out the significant guidance for SERS detection in colloidal solution.