An efficient antimicrobial depot for infectious site-targeted chemo-photothermal therapy

Silver and photothermal therapy (PTT) have been widely used for eradicating the drug-resistant bacteria. However, the risks of excess of silver for humans and the low efficiency of PTT still limit their in vivo therapeutic application. Integration of two distinctive bactericides into one entity is a promising platform to improve the efficiency of antimicrobial agents.

In this study, a chemo-photothermal therapeutic platform based on polydopamine (PDA)-coated gold nanorods (GNRs) was developed. The PDA coating acquired high Ag⁺ ions loading efficiency and Cy5-SE fluorescent agent labeled glycol chitosan (GCS) conjugation (Ag⁺-GCS-PDA@GNRs). This platform became positively charged in the low pH environment of the abscess, allowing their accumulation in local infection site as revealed by thermal/florescence imaging. The loaded Ag⁺ ions was released in a pH-sensitive manner, resulting in selective Ag⁺ ions delivery to the abscess environment (pH ~ 6.3). More importantly, the ultralow dose of Ag⁺ ions could effectively damage the bacterial membrane, causing the permeability increase and the heat resistance reduction of the cell membrane, leading to the large improvement on bactericidal efficiency of PTT. On the other hand, the hyperthermia could trigger more Ag⁺ ions release, resulting in further improvement on bactericidal efficiency of chemotherapy. Combinational chemo-hyperthermia therapy of Ag⁺-GCS-PDA@GNRs could thoroughly ablate abscess and accelerate wound healing via a synergistic antibacterial effect.

Our studies demonstrate that Ag⁺-GCS-PDA@GNRs is a robust and practical platform for use in chemo-thermal focal infection therapy with outstanding synergistic bacteria ablating.