Near field FEM simulations of plasmonic gold nanoparticle based SERS substrate with experimental validation

Surface enhanced Raman spectroscopy or surface enhanced Raman scattering (SERS) being a very powerful technique for quantitative and qualitative analysis finds application in low concentration detection of chemical and biological samples. In this work, we have presented a complete methodology of simulating nanoparticles-based SERS substrate. Different configurations namely single nanoparticle, dimer, trimer and tetramer nanoparticle clusters are simulated and enhancement factor for each configuration is estimated. Presented simulations are carried out with COMSOL Multiphysics software using Electromagnetic Waves module (Wave Optics) in frequency domain. The model of gold nanoparticle is established to determine the scatter field, which was further used to estimate the enhancement factor. Simulation results thus obtained are then validated with experimental results. The simulation study using the COMSOL Multiphysics tool helps in the design and development of the SERS substrate for maximum electromagnetic enhancement at a particular wavelength. The presented simulation methodology will be helpful for various SERS related computational studies in future. Presented approach helps in understanding the effect of various parameters such as particle size, inter particle gap, excitation wavelength, etc. on the EM enhancement. Simulating various possibilities before fabrication helps in saving money and time. For device realization, gold nanoparticles are synthesized using Turkevich method to achieve uniform and spherical nanoparticles. Synthesized nanoparticles (40–45 nm radius) were drop casted on a porous cellulose paper substrate to realize a SERS substrate. Nanogaps created between nanoparticles become the hot-spot locations leading to electromagnetic coupling and hence the Raman signal enhancement. Paper based SERS substrate is tested with Rhodamine B (1 μM) test sample. Enhancement of 106 was observed with the developed SERS substrate. UV–Vis spectrometer and Raman spectrometers are used for various characterizations.