New insights about the effect of cosolvent on the plasmon of gold nanoparticles of different sizes

A comprehensive study has been carried out on the effect caused on the localized surface plasmon resonance of gold nanoparticles (AuNPs) of different sizes by cosolvents formed by tetrahedral alcohols. Specifically, methanol, ethanol, 2-propanol and tert-butanol at different molar fractions and AuNPs of 5, 15 and 30 nm synthesized following a variant of the Turkevich chemical reduction method and characterized by electron microscopy and spectrophotometry techniques have been used. By applying Mie theory, theoretical absorption spectra have been obtained showing almost a null effect on the plasmon position after the addition of the cosolvent due to changes in the dielectric constant of the medium, exposing the importance of the structure of the medium, since, by increasing the hydrophobicity of the alcohol, a greater aggregation effect on the AuNPs has been found, which is also highlighted by increasing their size. The importance of future research is highlighted to understand the aggregation mechanism found, which could be the result of alcohol-alcohol, alcohol-stabilizer, or alcohol-metal surface interactions.