Simple Approach to Assess the Maximum Hot Spot SERS Enhancement Factors in Colloidal Dispersions of Gold Nanoparticle Aggregates

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.