Metal nanocrystal-based sensing platform for the quantification of water in water-ethanol mixtures

Abstract

Triangular silver (Ag) nanoplates with sharp corners exhibit fascinating optical properties, but their triangular shapes make them thermodynamically unstable. In the current work, we used this intrinsic instability as the basis for a novel sensing platform for the quantification of water in water-ethanol mixtures. Specifically, we designed a system that uses the color and spectral changes associated with the spontaneous rounding of the sharp corners of triangular Ag nanoplates exposed to bromide ions (Br−) to quantify the water fraction in water-ethanol mixtures. The rate of change of the color and spectral features of a water-ethanol mixture containing Ag nanoplates resulting from the introduction of KBr was found to be strongly correlated with the volume fraction of water in the mixture. This relationship, which was attributed to the dependence of the solubility of KBr on the volume fraction of water in water-ethanol mixtures, allowed the quantification of water in water-ethanol mixtures having any water volume fraction (from 0 to 1.0). The proposed colorimetric sensing platform exhibited reliable sensing results in two real products containing water and ethanol (an alcoholic beverage and an ethanol-based hand sanitizer). It was also successfully applied to determining the relative amount of water in water-isopropyl alcohol mixtures, suggesting that it can be applied to mixtures of water and other alcohols. The present findings suggest that the proposed nanocrystal-based sensing platform holds great potential for use as a point-of-care analytical tool for the quantification of water in the fine chemical, pharmaceutical, and food and beverage industries.