A water-soluble boronic acid sensor for caffeic acid based on double sites recognition

Due to reversibly and covalently binding with Lewis bases and polyols, boronic acid compounds as fluorescent sensors have been widely reported to recognize carbohydrates, ions, hydrogen peroxide, and so on. However, boronic acid sensors for highly selective recognition of caffeic acid rather than catechol or catechol derivatives have not been reported yet. Herein a novel water-soluble sensor 5c with double recognition sites based on a boronic acid was reported. When 2.3 × 10^-4 M of caffeic acid was added, the fluorescence intensity of sensor 5c decreased by 99.6% via inner filter effect (IFE) because its excitation spectrum well overlaps with the absorption spectrum of caffeic acid under neutral condition, while the fluorescence increased or did not change obviously after binding with other analytes including carbohydrates and other catechol derivatives. In addition, the response time to caffeic acid is fast at room temperature, and a high binding constant (9245.7 ± 348.3 M^-1) and low LOD (1.81 × 10^-6 M) was calculated. Moreover, determination of caffeic acid content in caffeic acid tablets was studied, and the recovery rate is sufficient. Therefore, sensor 5c can be used as a potential tool for detecting biologically significant caffeic acid in real samples.