Dual-mode antibacterial core-shell gold nanorod@mesoporous-silica/curcumin nanocomplexes for efficient photothermal and photodynamic therapy

Bacteria are becoming increasingly resistant to antibiotics because of their overuse. As a result, new therapies are urgently needed to replace traditional antibiotic therapies. Photodynamic therapy and photothermal therapy are considered to be effective sterilization methods instead of antibiotics to resist drug-resistant pathogens. In this work, silica-coated gold nanorods with photothermal conversion effects were employed as photothermal carriers, and curcumin was selected as photosensitizer, to form PTT/PDT dual-mode antibacterial nanocomposites (AuNRs@Cur). Comparing with their counterparts Cur and AuNRs, AuNRs@Cur exhibited higher singlet oxygen yield and photothermal conversion efficiency, which greatly improved the utilization rate of photosensitizer and consequently effectively enhanced the photoinactivation effect of bacteria. The inhibition rate of AuNRs@Cur on S. aureus and E. coli under 405 and 808 nm dual irradiation was higher than that of Cur or PDT alone. The changes of bacterial membrane structure were revealed by scanning electron microscopy (SEM) and confocal fluorescence imaging. The reactive oxygen species and thermal energy generated by dual-wavelength (405 + 808 nm) laser irradiation can cause the destruction of bacterial outer membrane structure, resulting in bacterial death. In addition, the cytotoxicity and hemolytic activity of AuNRs@Cur were negligible. AuNRs@Cur nanocomposites proved that   photodynamic-photothermal synergistic treatment can greatly improve the bactericidal effect. Therefore, construction of AuNRs@Cur provides a new idea for pathogen infection caused by drug-resistant bacteria, and provides relevant nano-carrier experience for follow-up drugs.