Portable and reusable HHSS@LaVO:Eu/polyacrylamide/sodium alginate for dynamic fluorescence switching detection of Fe 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:Eu/polyacrylamide/sodium alginate (HLE/PS) hydrogel was successfully constructed for portable dynamic fluorescence switching detection of Fe and encryption of security information. The HLE/PS hydrogel was synthesized from HHSS@LaVO:Eu 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 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 fluorescence by ultrasmall LaVO:Eu 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 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.