Development of a Chemical Sensor Based on Deep Eutectic Solvents and Its Application for Milk Analysis

Deep eutectic solvents (DESs) have unique physical and chemical properties, such as low vapor pressure, ease of synthesis, stability, and non-toxicity. Although they have found application in areas of research such as organic synthesis, electrochemistry, biocatalysis, and the development of biosensors, their use as sensitive coatings for chemical sensors has not been previously considered. This study examines the fundamental principles of generating sensitive coatings for piezoelectric quartz sensors utilizing hydrophilic deep eutectic solvents (choline + polyalcohols). Thin films from DESs with a melting point above 50 °C, including those in the composite coatings with amorphous silicon oxide, have been studied. The sorption characteristics of the coatings were thoroughly examined via piezoelectric quartz microbalance. It has been demonstrated that the limits of detection and determination of volatile organic compounds in aqueous solutions by films based on DESs exhibit lower limits than other polymer coatings. A novel approach is proposed for processing the kinetic curve of the sorption of volatile substances by films based on DES to improve the reliability and detection of volatile compounds in the gas phase above aqueous solutions. The use of DES-based piezoelectric quarts sensors has been demonstrated for assessing microbiological indicators of milk.