An <i>in situ</i> gas nanogenerator for pH-responsive controlled release and H ₂ S–chemo combined therapy <i>in vitro</i>

Developing smart nanosystems that integrate controlled drug release with gas therapy represents a promising strategy to enhance chemotherapeutic efficacy while minimizing systemic toxicity. Herein, we report a biodegradable <i>in situ</i> hydrogen sulfide (H₂S) nanogenerator based on ZnS nanoparticles (NPs) for pH-responsive co-delivery of H₂S and doxorubicin (DOX). ZnS NPs were synthesized <i>via</i> a rapid hydrothermal method and subsequently functionalized with hyaluronic acid (HA) to form ZnS@HA, which was then electrostatically loaded with DOX to yield ZnS@HA-DOX NPs. The nanosystem maintains structural integrity under physiological conditions (pH 7.4) but selectively releases both DOX and H₂S in an acidic tumor microenvironment (pH 5.0), as confirmed by fluorescence spectroscopy, lead acetate paper assays, and WSP-1 probe-based quantification. <i>In vitro</i> studies using 4T1 breast cancer cells revealed that ZnS@HA-DOX NPs exhibit significant cytotoxicity compared to ZnS@HA NPs alone, indicating a synergistic effect between H₂S gas therapy and chemotherapy. This work demonstrates the potential of ZnS-based nanogenerators as a multifunctional platform for pH-triggered, site-specific, and synergistic cancer therapy.