Visible light-induced controlled release and biological evaluation of bismuth sulfide quantum dots and silver nanoparticles co-sensitized titanium dioxide nanotubes

Controlled drug delivery has attracted significant attention because of its ability to release therapeutic agents at specific times and locations. Titanium dioxide nanotubes (TNTs), which are known for their unique tubular morphology, large surface area and excellent biocompatibility, have been widely investigated as drug carriers. However, their application in light-induced drug release is limited by their reliance on ultraviolet (UV) light. In this study, bismuth sulfide quantum dots (Bi₂S₃ QDs) and silver nanoparticles (Ag NPs) were used to co-sensitize TNTs, increasing their light absorption in the visible spectrum and effectively reducing the recombination of photogenerated carriers. The methylene blue (MB) degradation of the 1Bi₂S₃-4Ag@U-TNTs was 2.03 times greater than that of pristine U-TNTs within 120 min under visible light (k = 0.0072 min^-1). A double-layer drug release platform was subsequently fabricated, comprising an upper light-responsive layer (1Bi₂S₃-4Ag@U-TNTs, ∼2.01 μm) and a lower drug-loading layer (L-TNTs, ∼7.69 μm). Free radical scavenging experiments revealed that the superoxide radicals (•O₂ ^-) and hydroxyl radicals (•OH) generated by 1Bi₂S₃-4Ag@U-TNTs were the primary active species responsible for breaking the chemical bonds and releasing the drugs from the L-TNTs. The release efficiency of the 1Bi₂S₃-4Ag@U-TNTs/L-TNTs reached 91.38 % within 120 min, and maintained over 84.0 % after five cycles. The antibacterial assessment revealed that the 1Bi₂S₃-4Ag@U-TNTs/L-TNTs achieved nearly 100 % antibacterial efficacy against <i>E. coli</i> within 30 min, significantly outperforming the U-TNTs/L-TNTs (p < 0.001) while maintaining excellent biocompatibility. This visible light-induced drug release platform provides a novel approach for controlled drug delivery.