Silver Nanocube- and Nanowire-Based SERS Substrates for Ultra-low Detection of PATP and Thiram Molecules

The shape-anisotropic metal nanoparticles support large surface plasmon resonance (SPR) wavelength tuning and higher intrinsic electromagnetic hot spots for excellent surface-enhanced Raman spectroscopy (SERS) performance. Here, two shape-anisotropic nanostructures, silver nanocubes and nanowires with sharp features and high yield, are synthesized using the polyol reduction method. Finite-difference time-domain (FDTD) simulations are performed to understand the origin of the SPR peaks in the absorption spectra and for optimization of excitation wavelengths for large near-field enhancement. Silver nanocubes and nanowires exhibit broad plasmon resonances over the visible region of the electromagnetic spectrum with maxima around 498 nm and 410 nm, respectively. The SERS activity of nanocubes and nanowires are investigated for three molecules of different Raman activity. The SERS spectra show higher activity for nanocubes and ultra-low molecular detection (10(-15) M) capability of the fabricated substrates for rhodamine B (RhB) dye, p-aminothiophenol (PATP), and pesticide thiram. Relatively higher enhancement of some Raman modes is observed when excited with laser wavelength 532 nm indicating photo-induced charge transfer from metal to molecule.