A Novel Ion Species- and Ion Concentration-Dependent Anti-Counterfeiting Based on Ratiometric Fluorescence Sensing of CDs@MOF-Nanofibrous Films.

Traditional fluorescent anti-counterfeiting labels based on "on-off" fluorescence can be easily cloned. It is important to explore advanced anti-counterfeiting fluorescent labels with high-level security. Here, a pioneering ion species- and ion concentration-dependent anti-counterfeiting technique is developed. By successive loading Cu2+ -sensitive yellow emitted carbon dots (Y-CDs) and Cu2+ non-sensitive blue emitted carbon dots (B-CDs) into metal-organic frameworks (MOFs) and followed by electrospinning, the B&Y-CDs@MOF-nanofibrous films are prepared. The results show that the use of MOF not only avoids the fluorescence quenching of CDs but also improves the fluorescence stability. The fluorescence Cu2+ -sensitivity of the CDs@MOF-nanofibrous films can be regulated by polymer coating or lamination. The fluorescent label consisting of different Cu2+ -sensitivity films will show Cu2+ concentration-dependent decryption information. Only at a specific ion species and concentration (Cu2+ solution of 40-90 µm), the true information can be read out. Less or more concentration (<40 or >90 µm) will lead to false information. The identification of the real information depends on both the species and the concentration. After Cu2+ treatment, the fluorescence of the label can be recovered by ethylenediaminetetraacetic acid disodium (EDTA-2Na) for further recycling. This work will open up a new door for designing high-level fluorescent anti-counterfeiting labels.