Multicolor colorimetric tannic acid detection enabled by coordination-mediated oxygen vacancies modulation in MoOx nanosheets

Tannic acid (TA), a common polyphenol in food and beverages, is challenging to detect rapidly on-site due to limitations of conventional methods. Here, we present a colorimetric sensor based on oxygen-vacancy-rich molybdenum oxide nanosheets (MoOx, 2 < x < 3) for rapid, selective, and multi-color visualization of TA. The sensor exploits coordination between TA and Mo sites on MoOx, modulating localized surface plasmon resonance (LSPR) and shifting light-absorption of the MoOx-TA complex. UV-induced oxygen vacancies enhance the optical response, enabling fast color change from blue to green to yellow within seconds. Under optimized conditions, the sensor achieves a low detection limit of 0.31 μM and a linear range of 10–700 μM. With high selectivity against common interferents and antioxidants, and coupled with classification algorithms, it enables accurate TA determination in real samples. This work provides a robust, enzyme-free, cost-effective strategy for TA detection and a versatile tool for food quality control and on-site analysis.