We report plasmonic enhancement of Raman signal by employing silver nanotriangles to detect methylene blue in concentrations below 10-5 M. The characteristic morphology and dimensions have helped in producing an enhancement even at low power.

We present a method for detecting Methylene Blue (MB) using Confocal Raman Spectroscopy assisted with plasmonic enhancement from colloidal silver nanotriangles (NTs). The amplified Raman signal from the analyte aggregated over nanoclusters facilitated the detection of concentrations below 10 -5 M.Methylene blue and silver NTs were mixed in equal proportions and a thin film of the solution was drop casted on a glass slide for collecting Raman data. Raman signals were acquired from the plasmonic hotspots (PHs) present in the sample, using 532 nm laser excitation. PHs in the sample were identified as dark blue spots, as seen under confocal microscope. These PHs were formed by the adsorption of dye on aggregated NTs and give a stronger signal because of localised surface plasmon resonance (LSPR). The triangular morphology contributed to a better enhancement due to the lighting rod effect [1]. From experimental data, it is inferred that the limit of detection was well below the concentration reached, 0.25x10 -5 M.The main challenge to be addressed is the repeatability of the technique owing to the non-uniform and unstable hotspots scattered throughout the colloid. The reliability of this method can be increased with appropriate modification of the drop casting method to achieve a more uniform film. Considering the ease of implementation and cost-effectiveness, colloidal silver NTs are promising substrates in Surface Enhanced Raman Spectroscopy.

Simultaneous silver salt reduction and deposition at specific sites of graphene oxide films by femtosecond laser irradiation is achieved and Raman analysis corresponding to varying concentration of silver salt loading is investigated.