Graphene quantum dots as full-color and stimulus responsive fluorescence ink for information encryption

Developing anti-counterfeiting technique with rich information encrypted by cheap, eco-friendly and stable photoluminescent materials is useful yet challenging. Herein, we present the application of graphene quantum dots (GQDs) for full-color and stimuli-responsive information encryption. GQDs with red, green and blue (RGB) fluorescence or ion-responsiveness are prepared based on scalable bottom-up molecular fusion in one-step hydrothermal or solvothermal reaction. Printable fluorescent ink is easily prepared by dispersing GQDs homogeneously in glycerol-containing ethanol. Utilizing the color, pattern, characteristic fluorescence emission spectrum, or stimuli-responsive emission of GQDs, information encryption under daylight and information decryption under UV light are realized. Moreover, N and S co-doped GQDs (N, S-GQDs), which have Cu²⁺-quenchable and cysteine (Cys)-recoverable blue fluorescence, are mixed with lanthanide complex (Eu³⁺DP) to realize order-sensitive stimulus-responsive information encryption.