A naphthalimide based fluorescent liposomal system for sequential copper(II) and hydrogen sulfide detection and its application in hydrogel beads and bioimaging.

Hydrogen sulfide (H2S) is a key endogenous gaseous messenger, and its abnormal levels are closely linked to major physiological and pathological conditions. Developing selective and water-compatible H2S probes is therefore crucial. In this work, we report an amphiphilic naphthalimide-DPA-based fluorescent probe (Nap.Amp) capable of sequential Cu2+ and H2S detection via a fluorescence ON-OFF-ON mechanism. Nap.Amp exhibits strong green fluorescence that is quenched upon the formation of an in situ copper complex (Nap.Amp-Cu), which in turn displays excellent selectivity toward H2S, restoring the emission signal through copper displacement. To enhance aqueous solubility and sensing efficiency, Nap.Amp was incorporated into DOPC liposomes to generate nanoscale vesicles (Nap.Lipo). This liposomal system showed significantly improved Cu2+ affinity, forming nanoaggregates that served as a sensitive platform for H2S recognition. The Nap.Lipo-Cu ensemble detected H2S with a low LOD of 1.62 μM, and the sensing mechanism was validated using DLS and SEM analyses. Beyond solution-phase studies, Nap.Amp-Cu was adapted into portable test formats such as double-chamber gas sensors, paper strips, and alginate hydrogel beads for rapid, instrument-free H2S detection. Nap.Lipo also demonstrated excellent biocompatibility and enabled fluorescence imaging of H2S in L929 cells. Overall, this work presents the first demonstration of a liposome-incorporated naphthalimide-DPA probe (Nap.Amp) as a robust, versatile nanosensor for environmental and biological H2S detection.