Simple Approach to Assess the Maximum Hot Spot SERS Enhancement Factors in Colloidal Dispersions of Gold Nanoparticle Aggregates
Pablo A. Mercadal, Juan C. Fraire, Eduardo A. Coronado
Abstract
In recent work, a narrow distribution of nanoparticle (NP) aggregates in terms of the number of NPs and controlled interparticle distances has been obtained inducing NP aggregation with very low concentrations of a molecular linker, demonstrating that it is possible to determine the concentrations of the different aggregates using a suitable simulation of the extinction spectra. Herein, we introduce a new quantity denoted the single hot spot active concentration enhancement factor (SHSACEF) to assess in a rigorous way the surface-enhanced Raman spectroscopy (SERS) enhancement contribution. The SHSACEF discriminates the relative contributions to the overall SERS signal from the molecules located in each hot spot (HS) in a colloidal sample consisting of a mixture of NP aggregates of different sizes. The capabilities of this method is tested by inducing Au NP aggregation using a supramolecular complex (cucurbit[6]uril and methylviologen) and comparing the experimental values of the SHSACEF with theoretical simulations of the maximum enhancement generated for an individual HS in each nanoaggregate.