Visual detection of captopril based on the light activated oxidase-mimic activity of covalent organic framework

Light-activated mimic oxidase is a promising alternative of natural enzyme, in which oxygen molecule is decomposed with the catalysis of mimic oxidases under light radiation and the corresponding substrates are oxidized without H2O2. However, most of the reported light activated nanozymes are metal oxides and carbon-based nanomaterials, and there is still much room for exploration of new kinds of light activated nanozymes and improvement in light absorption capacity and substrate selectivity to extent their applications. Covalent organic frameworks (COFs) are porous crystalline polymers and have been widely applied in photocatalysis due to the versatile chemical stability and extended π-conjugated framework. Herein, a new nitrogen-rich triazine-containing COF (TTA-Tp COF) was illustrated to exhibit light activated oxidase mimic activity. Under white LED irradiation, the oxidase-mimic activity of TTA-Tp COF was dramatically enhanced and the colorless solution visibly changed to blue within 10 min using 3, 3′, 5, 5′-tetramethylbenzydine (TMB) as substrate. Further study demonstrated that the enhanced oxidase-mimic activity might be accounted for the increased π-electron communication and light harvest efficiency ascribing from the fully conjugated feature of TTA-Tp COF, and thus TTA-Tp COF could be easily excited under visible light to generate reactive oxygen species (ROS) in the presence of dissolved oxygen which oxidized TMB to its oxidized blue product. As a mimic oxidase, TTA-Tp COF has the advantages of easy light control, excellent catalytic oxidation ability and good stability. Moreover, the light activated oxidase mimic activity of TTA-Tp COF was applied to visually detect captopril, and the linear range is 1.0 to 100.0 μM (R2 = 0.992) with a detection limit of 0.78 μM (3σ/K). The TTA-Tp COF based colorimetric method also had a good selectivity, and the measured captopril concentration in captopril tablet was identical to that obtained by the standard method. Moreover, the spiked experiments for tablet samples and 100 folds diluted human serum samples received recoveries ranging from 91.9 to 105.6%, suggesting a high accuracy of the present TTA-Tp COF based colorimetric method.