Synthesis and SERS Activity of Core-Satellite Nanoparticles using Heterobifunctional PEG linkers

Surface-enhanced Raman spectroscopy (SERS) is a sensitive analytical technique, capable of magnifying the vibrational intensity of a molecule absorbed onto the surface of metallic nanostructures. Various solution-based SERS-active metallic nanostructures have been designed to generate strong SERS enhancements. However, most of these SERS substrates rely on the chemical aggregation of metallic nanostructures and although this can induce high SERS intensities through plasmonic coupling, most suffer from poor signal reproducibility and reduced long-term stability limiting their use in analytical applications. To overcome these issues here we report, the synthesis of gold core-satellite nanoparticles (Au-CSNPs) for robust SERS signal generation. The novel CSNP assembly consists of a 30 nm core linked to 18 nm satellite particles via a linear heterobifunctional thiol-amine terminated PEG chains. We explore the effects that the varying chain lengths have on SERS hot-spot generation, signal reproducibility and long-term activity. The chain length was varied by using PEGs with different molecular weights (1000 Da, 2000 Da, 3500 Da). The CSNPs were characterized via UV-Vis spectrophotometry, transmission electron microscopy (TEM), ζ-potential measurements, and lastly SERS measurements. The versatility of the synthesized SERS-active CSNPs were revealed through characterization of optical stability and SERS enhancement at 0,1, 3, 5, 7 and 14 days.