Erythrosine B – coated gold nanoparticles as an analytical sensing tool for the proper determination of both compounds based on surface-enhanced Raman spectroscopy

•Double SERS sensing methodology for determining AuNPs and erythrosine B.•Erythrosine B as Raman reporter.•Charge-transfer effect as additional enhancement mechanism.•Highly sensitive indirect determination of AuNPs through an erythrosine-assisted SERS method.•Contribution to analytical nanometrology. An analytical sensor for gold nanoparticles (AuNPs) and erythrosine B, based on surface-enhanced Raman spectroscopy (SERS) using a specially designed nanostructured substrate is reported. It is well documented that highly conjugated organic molecules, such as food dyes, display a strong additional charge-transfer effect when adsorbed on the AuNPs metallic surface, exhibiting good abilities to act as Raman reporters. In this work, five synthetic food dyes were selected and studied as AuNPs sensor molecules. Erythrosine B showed the highest AuNPs-binding affinity due to its greater enhancement of the Raman signal with respect to the other dyes tested. Thus, this dye was selected to be part of the sensor. This fact allowed the development of an analytical sensor for both AuNPs and erythrosine B. The optimal performance conditions of the sensor for both analytes were studied, showing to be especially sensitive for the determination of AuNPs. A linear relationship exists between the SERS signal intensity and AuNPs in the 1.0 to 12.0 ng L−1 range and between 5.0 and 150.0 µg L−1 for erythrosine. Detection limits (LODs) were 0.3 ng L−1 and 1.4 µg L−1 for AuNPs and erythrosine B, respectively. The potential of this analytical method was demonstrated by applying it to the quantification of AuNPs in enriched environmental, biological and cosmetic samples, and of erythrosine B in food samples. The proposed analytical approach satisfies the need for a simple, quick and sensitive methodology to determine AuNPs in samples of interest, thus contributing to analytical nanometrology.