Synthesis of anisotropic silver-coated nanoworms for sensitive SERS detection of crystal violet and ammonium nitrate.

Abstract

Silver (Ag)-coated nanostructures (NSs) are exceptionally promising for surface-enhanced Raman scattering (SERS) spectroscopy-based trace detection of molecules due to their superior plasmonic properties. However, the effect of Ag coating on nanoworms (NWs), particularly for SERS applications, is less explored. Herein, we report anisotropic Ag-coated NWs (Ag@NWs) that exhibit excellent SERS sensitivity. In particular, we report the formation of an anisotropic Ag shell on NWs using the seeded method. The wavy morphology of these NWs, along with the optimized reaction conditions during the seeded method, enables the formation of a highly anisotropic Ag shell structure without secondary nucleation inside the growth solution or agglomeration. Finite difference time domain simulations confirm that the anisotropic Ag@NWs are more effective for field enhancement than the NWs, both in the isolated and aggregated states. Furthermore, the anisotropic Ag shell generates significantly higher field enhancement than its isotropic counterpart around the core NW. We provide the first experimental evidence of the excellent SERS sensitivity of Ag@NWs and provide a comparison of the SERS performance of the NWs and Ag@NWs using crystal violet as a probe molecule. Ag@NWs provided a 3.5-fold higher analytical enhancement factor than the NWs and accomplished a detection limit of ten picomolar and ten micromolar for crystal violet and ammonium nitrate, respectively. These findings show that the integration of an anisotropic Ag shell significantly improves the SERS performance of the NWs, and Ag@NWs serves as an ultrasensitive nanomaterial for quantitative trace detection of analytes.

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