Controlled assembly of one-dimensional MoO₃@Au hybrid nanostructures as SERS substrates for sensitive melamine detection

A new, feasible, and highly efficient platform was developed using self-assembly of (3-aminopropyl) diethoxymethylsilane (ATES) to create metallic oxide-based noble metal nanoparticle hybrid materials. The ex situ approach for fabricating 1D MoO₃-nanowires (MoO₃-NWs) or ZnO-nanorods (ZnO-NRs) @Au-nanoparticles (Au-NPs) hybrid surface-enhanced Raman scattering (SERS) substrates not only provides a simple route for the decoration of noble metal nanoparticle on metallic oxide nanomaterials, but also realizes the controllable assembly/co-assembly of pre-synthesized nanoparticles with distinctively different sizes, compositions, shapes, and properties. Control over the self-assembly synthesis for morphology and SERS activity was demonstrated by several parameters: (i) coupling agent of ATES, (ii) ATES content, (iii) Au-NPs content, (iv) Au-NP sizes, and (v) other metallic oxide such as ZnO-NRs. The finite difference time domain (FDTD) method was employed to visualize the enhancement mechanism distribution of the hybrid substrate. Furthermore, the optimized MoO₃-NW@Au-NPs SERS substrate manifests high SERS sensitivity to melamine with a limit of detection (LOD) of 0.1 ppb (0.08 nM) and excellent uniformity (RSD = 9.26%). The LOD was much lower than the maximal residue limit (MRL) of 2.5 ppm in food prescribed by the US Food and Drug Administration (FDA).