Internal magnetic driven self-assembly of gold-nickel nanowires as SERS substrate for thiram fungicide detection using handheld Raman spectrometer

Abstract Designing three-dimensional (3D) arrays of metal nanomaterials without linker molecules is challenging for the fabrication of high-performance surface-enhanced Raman scattering (SERS) substrates. In this study, self-assembly of bi-segmented gold-nickel nanowires (Au-Ni NWs) solely driven by internal magnetic coupling of Ni tips was developed for fabrication of SERS substrates. Au-Ni NWs were fabricated using template-based electrodeposition technique. The variation of Au-Ni NWs arrangement was strongly influenced by aspect ratios of Ni segment. SERS intensity and Raman mapping measurements of 4-mercaptobenzoic acid (4-MBA) coated Au-Ni NWs were performed to evaluate analytical enhancement factor (EF) and hotspot location. The tip-to-tip Au-Ni NWs orientation so-called hybrid structure between firecracker and star arrangements gave the strongest EF about 106 and the largest SERS hotspot regions. These developed Au-Ni NWs arrayed on silicon wafers were used as SERS substrates for a demonstration of thiram detection. The linear response was in the range of 100 to 800 ppb with about 29.7 ppb limit of detection. As a proof of concept, a study for feasibility test of thiram contaminated watermelon seed detection was evaluated using handheld Raman spectrometer. This sensing platform could be used for on-site rapid detection of fungicide residual in biological samples.