Nanostructure, solvation dynamics, and nanotemplating of plasmonically active SERS substrate in reverse vesicles

Reverse vesicles (RVs) are the organic counterparts to vesicles and are spherical containers in oils consisting of an oily core surrounded by reverse bilayers with water layers present in between. We present here a facile route for forming stable RV from nontoxic surfactants and oil components. The RV formation is characterized by dynamic light scattering and further confirmed by transmission electron microscopic (TEM) techniques. The water channels present in between the bilayers are found to be a potential template for inorganic nanoparticles’ (NPs) synthesis. Both the UV–Vis absorption spectroscopy and the TEM study reveal successful formation of highly clustered silver NPs within the water layers of the RVs. X-ray powder diffraction analyzes the crystalline nature of the NPs. FTIR spectroscopy shows the signature of different kinds of water molecules in between the RV bilayers. The dynamical description of the templating water, dictating the controlled formation of the NPs in the RV, is well revealed in the picosecond-resolved solvation dynamics study of a hydrophilic fluorescence probe 2′-(4-hydroxyphenyl)-5-[5-(4-methylpiperazine-1-yl)-benzimidazo-2-yl-benzimidazole] (H258). The rotational anisotropy study successfully describes geometrical restriction of the probe molecule in the RV. Notably, this study provides the first proof-of-concept data for the ability of the RV to be a template of synthesizing metal NPs. The as-prepared NP clusters are evaluated to be potential surface-enhanced Raman scattering substrate in solution using crystal violet as a model analyte. The present study offers a new RV, which is a prospective nontoxic nanotemplate and is believed to contribute potentially in the emerging NP-vesicle hybrid assembly-based plasmonic applications.