Silica coated gold nanorods (GNRs@SiO 2 ) with dumbbell-like morphology allowing dual functionalization in an individual nanostructure have attracted great attention for applications such as sensing and biological imaging. We report a detailed study on the feasibility of controlling the morphology of silica coating on GNRs. The morphology of the silica shell can be either cylindrical or dumbbell shaped. With constant GNR concentration, the ratio of hexadecyltrimethylammonium bromide (CTAB) and tetraethylorthosilicate (TEOS) concentrations is the key to determine the amount of available TEOS for silica deposition on the GNR since the TEOS will diffuse toward the surface of GNRs. The effect of morphologies on surface-enhanced Raman scattering (SERS) performance was also investigated, and we found that the dumbbell morphology of silica coated gold nanorods has the most significant SERS enhancement. Our study is significant in terms of the capability to control the dumbbell morphology of silica coated gold nanorods, which can eventually broaden the application of these plasmonic nanomaterials.

Gold nanorods (AuNRs) have emerged as a powerful element in the development of nanomaterial-based sensors due to their localized surface plasmon resonance extinction at visible and near-infrared wavelengths. In this study, we present a strategy for plasmonic detection of mercury using PEG-thiol-coated AuNRs (PEG@AuNRs). The PEG@AuNRs, prepared by a simple ligand exchange, demonstrate superior advantages including sensitivity, stability, and specificity than the as-synthesized hexadecyltrimethylammonium bromide-coated AuNRs. The plasmonic responses of PEG@AuNRs toward the same amount of Hg in the system can be significantly manipulated by adjusting the AuNR concentration in the system and the incubation time between AuNRs and Hg 2+ . Both Hg 2+ −S complexation and amalgam formation contribute to the unique behavior of plasmonic response which enable the design of a smart Hg 2+ -sensing platform with an adjustable peak plasmonic response region. This study not only demonstrates the advantages of mercury-sensing systems based on PEG@AuNRs but also advances the fundamental understanding of ligand impacts on plasmonic properties for the plasmonic detection of mercury.

It has been shown that controlling the morphology and composition of Pt-based nanocrystals can effectively enhance catalytic properties. We report a detailed study on the impact of using co-reducing agents in the galvanic replacement reaction (GRR) between Ag shell templates and Pt precursors to better control the morphology, composition, and resulting performance of the fabricated Pt-based catalysts. Mesoporous silica-supported silver shell-coated gold nanodumbbell nanostructures (AuNDB@Ag@mSiO2) are synthesized via reducing silver ions which have penetrated through the mSiO2 layer and then be deposited on the surface of the AuNDBs. These are used as templates and the morphology and optical properties of these templates can be adjusted by altering the amount of Ag+ in the depositing condition. The mSiO2 layer shows some flexibility and does not influence the silver shell formation on the surface of AuNDBs. Additionally, the thickness of the silver shell of the template and the strength of the reducing agent used in the GRR impact the morphology, composition, and catalysis performance of the resulting Pt-based catalysts. A plausible mechanism on those observations is studied and discussed.