Covalent organic framework-assisted solar energy storage in long-lived organic radicals for enzyme-free colorimetric detection of xanthine

Abstract

Xanthine monitoring is meaningful for both human health and food industrial, but rapid, cost-saving and natural enzyme-free detection of xanthine is still a big challenge. Herein, a new covalent organic framework (FPPy-TSC COF) with unique photoelectric properties is developed for rapid, enzyme-free and sensitive colorimetric detection of xanthine in complex real samples. In the presence of xanthine, FPPy-TSC COF interacts with xanthine through hydrogen bonds, and the electrons generated by FPPy-TSC COF under light irradiation can be transferred to xanthine with the result of storing solar energy in the form of long-lived organic radicals. Then the electrons stored in xanthine gradually reduce dissolved oxygen to oxygen radicals under dark conditions, which subsequently catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized products (oxTMB). Based on the characteristic absorption and color changes, xanthine can be detected under dark condition by naked eyes, spectrometry and smartphone with the detection limit low to 3.23μM (3σ/K). Moreover, xanthine contents in serum and pork samples can be accurately detected with the recoveries ranging from 95.28 to 107.34%. This work not only proposes a novel enzyme-free detection system for xanthine, but also broadens the sensing application of COF nanozymes under dark condition.