Influence of the Particle Shape and Density of Self-Assembled Gold Nanoparticle Sensors on LSPR and SERS

A low-cost methodology to prepare highly sensitive sensors is reported with different nanoparticles for LSPR and SERS measurements. The LSPR and SERS sensor was self-assembled as an array of polystyrene-capped gold nanoparticles (Au NPs), produced by drop-coating a Au NP suspension on a glass surface followed by plasma etching of the polystyrene. The procedure was applied to different sizes and shapes of Au NPs, primarily 60 nm gold nanospheres and 80 nm gold nanoraspberries, created with precise control on the packing density of the array. The LSPR sensitivity and figure of merit (FOM) for the arrays of gold nanoraspberries were found to be almost 2-fold better than for the nanospheres and had a shorter penetration depth, a consequence of their small-sized surface asperities. The average measured SERS enhancement factor (EF) for the raspberries was also higher than for spheres and control over the EF was achieved using different packing densities which allowed control of the interparticle coupling enhancing the SERS response. The localized EF (hot spot) in dense arrays of nanoraspberries was measured to be in the order of a typical EF required for single molecule SERS, as demonstrated from the general agreement of experimental measurements with simulations performed using Comsol Multiphysics. This simple LSPR and SERS sensor could potentially serve as an effective platform for the identification and quantification of various analytes.