Molecular Sensing Efficiency of Gold-Silver Alloy Nanowires

Abstract

Noble metal nanomaterials with a controlled dimension and shape have attracted much attention for their unique physical and chemical properties such as tunable surface plasmonics, surface enhanced Raman scattering (SERS), high-efficiency electrochemical sensing, enhanced fluorescence, and quantum conductance for the last decade. Surface plasmon resonance characteristics are highly affected by size, shape, and morphology of noble metal nanomaterials. In the case of silver (Ag) nanomaterials, plasmonic resonance absorption is typically observed in the wide spectral range from ultraviolet (for nanoparticles) to near-infrared (for high aspect ratio nanowires). Gold (Au) nanomaterials also have tailorable plasmonic characteristics, and there are facile accessible routes to synthesize well-featured nanomaterials. Recently, porous gold (p-Au) materials have been developed in different morphology and pore size in order to use them as good SERS substrates because nanopores act as SERS ‘hot spot’. Porous gold materials are rationally synthesized through electrochemical gold-silver alloying and silver dealloying route. If the alloying-dealloying route processes in a cylindrical nanopore (e.g., in anodic aluminum oxide membrane), p-Au has a one-dimensional (1D) morphology (i.e., nanowire). Meanwhile, the composite form of gold-silver (AuAg) alloy has also been synthesized in the different morphologies of particle, wire, and cage in nanometer size. An alloy nanoparticle supported in a mesoporous matrix has been used as a catalyst for carbon monoxide oxidation. Unusual electron dynamics is observed in alloy nanoparticles due to a nonequilibrium electron distribution. A recent notable report is that AuAg alloy nanocage shows bright three-photon luminescence which enables ultrasensitive and high contrast imaging for biological samples (e.g., cells, tissues, etc.). Even though AuAg alloy nanomaterials have unique characteristics, there is still a limited study on molecular sensing application using them. In this study, we prepared AuAg alloy nanowires (NWs) through templating route using anodic aluminum oxide (AAO) templates, and used them as SERS platforms. AuAg alloy was electrochemically deposited in nanocylindrical nanopores, and then the AAO hard template was completely removed by a HF aqueous solution. The resulting alloy nanowires are dispersed in a cresyl violet acetate (CV) solution (1 × 10 M) under sonication. Raman spectrum was