Metal ion-induced multifunctionality in luminescent hydrogels for information encryption and mercury ion detection

[Display omitted] •A metal ion-induced strategy to construct a multifunctional hydrogel.•This strategy utilizes Au-induced luminescence, Zn2+-induced shape memory, and Hg2+-induced fluorescence quenching.•This hydrogel exhibited fluorescence, shape memory effect and ionic conductivity properties.•Simple and versatile construction of three-dimensional encryption platforms and detection of Hg2+.•Information is written by Hg2+ and protected by Zn2+ fixing the shape, which is read under shape recovery and UV irradiation. Information security has long been a focal point of research. However, the development of cryptographic hydrogels endowed with both high security and multifunctionality remains a challenge. Herein, we reported a method to construct multifunctional hydrogels using a metal ion-induced strategy. Leveraging Au- induced luminescence, Zn2+- induced shape memory, and Hg2+- induced fluorescence quenching, our method engendered a suite of distinctive properties, including fluorescence, shape memory effects, and ionic conductivity. Tunable fluorescence was utilized for detecting Hg2+ with a detection limit as low as 0.0007 μmol/L. Additionally, a successful design of a multilevel information encryption platform, ranging from 2D to 3D, was achieved by combining the aforementioned properties. The information written using Hg2+ as ink can be protected by the fixed shape of Zn2+, and the encrypted information can only be read under the conditions of shape recovery and UV irradiation. This simple yet effective strategy demonstrates a promising future for the application of this hydrogel in information encryption.