Construction of borate-ester-based COFs with high specific surface area for the detection of H2O content in the food field

Excessive H2O content in food will cause the hydrolysis of nutrients and provide a favorable environment for the growth of mycotoxins, thus, developing fast response, low detection limit, and high detection capacity sensors is urgently needed for food quality and safety. In this work, we developed two borate-ester-based covalent organic frameworks (COF-5 and COF-10) with high specific surface areas (1189.0 m2·g−1 and 1105.1 m2·g−1), which exhibited rapid response (COF-5 about 40 s and COF-10 about 35 s), good linearity (COF-5:R2 = 0.9981 and COF-10:R2 = 0.9993), and low detection limits (LODCOF-5 = 0.044 v/v% and LODCOF-10 = 0.016 v/v%). DFT theoretical calculation demonstrated that H2O participated in the partial hydrolysis of the B-O bond, resulting in the enhancement of fluorescence. Based on the good fluorescence properties, these two probes had been successfully used to quantificationally detect H2O content in honey, corn starch, and milk powder with satisfactory results, indicating an excellent application potential in the food field.