Photothermal Bacterial Clearance Using Gold Nanoshells Grown on Chitosan Nanoparticles Dielectric Templates

Bacterial infections remain among the top ten major public health concerns, contributing to a high number incidence of disease and mortality worldwide. This issue has been exacerbated by the rise of multidrug-resistant bacteria (MDRB). Consequently, it is crucial to develop novel antimicrobial strategies, including the use of functional nanoparticles. Gold nanoparticles (GNPs) have emerged as promising candidates due to their unique optical properties, particularly their ability to efficiently convert absorbed light into heat through the photothermal (PT) effect, which can be harnessed for bacteria eradication. In this study, gold nanoshells (GNSs) were synthesized and proposed as photothermal devices to bacteria clearance via PT. First, chitosan was modified with 3-mercaptopropionic acid to introduce sulfur groups, facilitating gold deposition onto chitosan nanoparticle surface. Thiolated chitosan nanoparticles (TCNPs), with a size of 178 nm and spherical morphology were synthesized using the ionic gelation method. The gold shell was subsequently formed via a seed-mediated method, wherein gold seeds were adsorbed onto TCNPs and further grown to form the shell. The resulting TCNP@Au exhibited a photothermal conversion efficiency of 31%, making them a promising photothermal agent for bacterial clearance. Notably, the viability of Escherichia coli was significantly reduced in the presence of TCNP@Au and was almost eradicated upon PT treatment, with viability dropping to 0.3 %. In contrast, TCNP@Au were non-toxic for Staphylococcus aureus. Interestingly, S. aureus exhibited a reduced susceptibility to the PT effect, maintaining a viability of 76 % after the laser irradiation treatment. Despite these results, TCNP@Au demonstrated favorable photothermal properties, presenting a novel nanoplatform for antibacterial applications, particularly against Gram-negative bacteria. However, further investigation is required to optimize the PT-based strategies against Gram-positive bacteria, such as S. aureus.