Superparticles of gold nanorods with controllable bandwidth and spectral shape for lipophilic SERS

The plasmonic nanoparticle components assembled by certain methods have great application potential in single particle scattering and surface-enhanced Raman spectroscopy (SERS) detection. Gold nanorods (GNRs) are a type of promising plasmonic material for nanoparticle assembly due to their large, shape-induced local field enhancement and tunable surface plasmon resonances (SPRs). However, it is difficult to obtain the spectra of the anticipated bandwidth and shape, due to the coupling effect between the GNRs and the concentration of GNRs with different SPRs. In this paper, a superparticle assembly method with predictable spectral bandwidth and shape prepared by batch gradient descent (BGD) algorithm fitting and emulsion method is proposed. Specifically, broadband GNRs were obtained by mixing 6 types of GNRs, which the ratios were determined by a BGD algorithm. Then the superparticles were prepared by a method of oil-in-water emulsion with solvent evaporation, resulting in superparticles with broadband spectra from 700 nm to 1100 nm. The bandwidth and shape of the spectra could be tuned by changing the concentration of GNRs of different LSPRs. After removing the CTAB template of mesoporous silica, the assembled broadband superparticles can also measure SERS enhancement for the lipophilic dye molecule Nile red, which opens up a broad space for its sensing application.