Sugar detection using drop evaporation

Evaporation deposition of a spilt sugary drop on the supporting surface can attract ants to surround it. People have a long history of using this phenomenon as an implication of sugar in the drop. Unfortunately, it is hard to detect sugar concentration and has to depend exclusively on ants. Here, we show a facile strategy for the eye-naked detection on sugar concentrations in common liquid mixtures, based on their evaporation depositions. Our experiments show that evaporation drops without any sugar form clear ring-like depositions, and the width of the ring area enlarges with the increase in sugar concentration. We demonstrate that the increase in sugar concentration can increase the liquid viscosity and decrease the capillary flow velocity, thus weakening the “coffee ring” effect. Our further experiments indicate that the temperature has insignificant effects on the correlation between sugar concentrations and ring-like depositions, but the substrate wettability impacts on the correlation by promoting the formation of ring-like depositions. Based on the mechanism study, we develop a strategy for detecting sugar concentrations via quantitatively correlating them with the width of the ring area, and demonstrate that it is valid for various liquid mixtures, for example, carbonate beverage, liquid medicine, and plant nutrient. Our findings not only present new insights into the understanding of the sugary drop evaporation, but also provide a facile strategy of detecting sugar concentration that promises great applications in food safety, pharmaceutical detection, and agricultural product measurements.