Portable and reusable HHSS@LaVO4:Eu3+/polyacrylamide/sodium alginate for dynamic fluorescence switching detection of Fe3+ and secure information encryption

Portable and reusable solid-state fluorescence sensors have received much attention in the field of metal ion detection as a superior alternative to traditional liquid-based fluorescence sensors. In this study, a novel HHSS@LaVO 4 :Eu 3+ /polyacrylamide/sodium alginate (HLE/PS) hydrogel was successfully constructed for portable dynamic fluorescence switching detection of Fe 3+ and encryption of security information. The HLE/PS hydrogel was synthesized from HHSS@LaVO 4 :Eu 3+ fluorescent nanofillers embedded in a semi-IPN network of polyacrylamide (PAM) and sodium alginate (SA). The HLE/PS hydrogel has demonstrated excellent performance in the detection of Fe 3+ in aqueous solutions with high selectivity, high sensitivity, fast response (8 min), wide detection range (2–1000 μM), low detection limit (0.78 μM) and ease of use. It can be reused up to five times, underlining its utility and economy as a good performance fluorescence sensor. Notably, the quenching of Fe 3+ fluorescence by ultrasmall LaVO 4 :Eu 3+ nanoparticles on HHSS supports was significantly enhanced compared to conventional large-sized rare earth phosphor fillers. Additionally, by exploiting the reversible fluorescence switching function of the HLE/PS hydrogel, we further developed a high-security multi-layer information encryption platform. Finally, we thoroughly investigated the fluorescence response mechanism of HLE/PS hydrogels to Fe 3+ ions. This work not only provides a representative case for the preparation of packed rare-earth fluorescent hydrogels, but also demonstrates their potential as multifunctional smart luminescent materials.