Core-shell gold @silver hollow nanocubes for higher SERS enhancement and non-enzymatic biosensor

Abstract

Here we report a simple low-cost method to produce surface-enhanced Raman scattering (SERS) substrates with improved efficiency and high sensitivity towards uric acid and ascorbic acid sensing using non-enzymatic amperometric electrochemical method. Trisoctahedral gold (Au) core-silver (Ag) shell cubical shaped nanoparticles were synthesized simply by varying the surfactant in the reaction medium, and afterwards we made them hollow by galvanic displacement reaction. Spherical core-shell nanoparticles (both solid and hollow) were also prepared to compare results with cubical one. We have performed transmission electron microscopy (TEM) studies to understand the morphology of these nanoparticles and UV–vis–NIR and Raman spectroscopy studies to understand optical properties. We have obtained a huge SERS enhancement (~109) for hollow Au@Ag nanocube using 4-mercapto benzoic acid (4-MBA) as analyte. Because of the very thin Ag shell wall, both core Au and shell Ag interacts with the incoming electromagnetic wave, and also due to the presence of multiple sharp edges and corners in both core and shell part of the nanoparticles there is a large enhancement of the electromagnetic field. We have performed cyclic voltammetry study using the nanoparticles as electrode to understand how interfacial charge transfer and electron accumulation is happening in between an electrode and electrolyte interface and we have obtained a very high current response for hollow core-shell nanocube due to more surface area. High current response with voltage enable us to use hollow core-shell nanocubes as non-enzymatic electrochemical sensor for sensing uric acid (UA) and ascorbic acid (AA). We found a good sensitivity (1.509 μAmM−1cm−2 and 209.027 μAmM−1cm−2 for UA and AA, respectively) and very low detection limit (0.36 μM and 0.019 μM for UA and AA, respectively) towards sensing, which allows us to use Au@Ag hollow nanocube as a good UA and AA sensors.