Au confined covalent organic frameworks nanoenzyme integrated with sodium alginate microsphere for portable...

Developing a portable, affordable, and instrument-free colorimetric sensor for tannic acid detection is crucial for food quality assessment and health monitoring. In this work, we designed a rapid and efficient colorimetric platform by integrating Au-modified covalent organic framework (COF) with sodium alginate hydrogel microspheres for tannic acid detection assisted by mobile phone photo technology. The Au NPs with an average size of 4 nm were reduced by the bipyridine nitrogen on the COF layer under light irradiation, which enhanced the peroxidase-like activity of the nanozyme. Furthermore, the adsorption, hydrogen-bond, and covalent interaction between tannic acid and sodium alginate make the functional hydrogel microspheres exhibit enhanced colorimetric performance, with a linear range from 5.0 to 130 μM and a detection limit of 0.091 μM. In addition, the obtained colorimetric sensor was effectively used for tannic acid analysis in grape beverages and model wine samples with good recovery. This work broadens the horizon for the synthesis and design of visual sensors with functional porous COFs-based nanozyme and the development of portable and low-cost sensors by combining hydrogel microspheres, which could be applied for food analysis and quality control in real environments.