Statistical Correlation Between SERS Intensity and Nanoparticle Cluster Size

Abstract

Surface enhanced Raman scattering (SERS) mapping of biomarkers has shown great promise in determining the distribution of proteins of interest in cells and tissues. Metallic nanoparticle (NP) probes are generally used in such mapping. Since SERS intensities from NPs are dependent on size, shape, and interparticle distance/distribution, it is unclear if this method can provide reliable biomarker quantification. To address this problem, we investigated a statistical approach to the quantification of SERS from SERS probe clusters. The investigation began by considering multiple biotinylated surfaces that had been exposed to pegylated NPs (designed for biological SERS mapping) functionalized with streptavidin (defined as SERS probes). The surfaces were imaged with a scanning electron microscope and SERS-mapped with a Raman microscope. Statistical distributions of the SERS probe clusters and mapped SERS intensities on the surfaces were developed. It was found that there was a smooth polynomial relationship between SERS intensity and probe cluster size. Our result is in contrast to the sharp, highly variable intensity increases observed in studies of unmodified NPs. Based on the polynomial relationship found, it is clear that pegylated NP SERS probes might be useful for quantification in the SERS mapping of biological material, as the SERS intensity can be potentially related back to the number of probes at the acquisition point.