Multicolour colorimetric/fluorescent dual-signal sensor based on carbon dot nanoenzymes-red emitting carbon dots-TMB for highly selective detection of tannic acid

Carbon dots (CDs) with both fluorescence and nanozyme activity are regarded as excellent probe for developing fluorescence/colorimetric dual-mode sensing systems. The sensitive, selective, rapid and portable detection of the natural polyphenol antioxidant tannic acid (TA) is of great significance. This study reports the employment of green-emitting carbon dots with peroxidase-like activity (Fe-CDs) and red-emitting carbon dots (R-CDs) as dual probes to establish a fluorescence/colorimetric dual-mode sensing biosensor to realize the detection of tannic acid. With the presence of hydrogen peroxide, Fe-CDs catalyze the oxidation of TMB to produce a blue product (OX-TMB), causing the color solution change from red to blue. Meanwhile, the fluorescence of the sensing platform weakens with blueshift in emission wavelength because of the inner filter effect (IFE). Because TA can effectively inhibit the Fe-CDs/TMB chromogenic reaction, its presence leads to the recovery of both solution color and fluorescence intensity. This sensing platform exhibits good selectivity, anti-interference ability to various antioxidants. The colorimetric and fluorescence sensors demonstrate excellent linear relationships within the concentration ranges of 8–600 nM and 8–1000 nM, respectively, with detection limits as low as 4.54 nM and 7.47 nM. A portable hydrogel-based detection platform was then developed, enabling multi-color colorimetric/fluorescence dual-channel visual detection either by the naked eye or with smartphone assistance. The system has been successfully applied to detection TA in real samples with recovery rates at 95.51–107.87%. This research provides a novel dual-signal verification strategy for the highly sensitive and selective detection of natural antioxidants and offers a new approach for the real-time analysis of active components in complex matrices.