One-Pot, Surfactant-Free Synthesis of Gold Nanostars and Evaluation of Their Antibacterial Effects against Propionibacterium acnes

Abstract

Anisotropic gold nanoparticles, especially gold nanostars, are used in many fields of biomedical applications such as sensing, targeted drug delivery, and diagnostic and photothermal therapy. In this study, we introduced a novel application of gold nanostars as an antimicrobial agent. While spherical gold nanoparticles have an inappreciable effect, gold nanostars exhibit significant antibacterial activity. Besides, the seed-mediated method, a conventional technique for preparing gold nanostars, is rather complex and toxic to human and environment due to unsafe synthesized materials such as surfactants and reducers. In recent years, green chemistry for nanoparticle synthesis is attractive because of its advantages. Instead of the seed-mediated procedure, we present a facile and green procedure to synthesize gold nanostars using ascorbic acid as a reductant and chitosan as a directing-growth agent. The influences of reacting parameters were evaluated to determine the optimal conditions. Star-shaped gold nanoparticles were successfully synthesized with average size tunning from $137.0\pm 20.7\text{nm}$ to $281.9\pm 25.8\text{nm}$ of the core and $14.0\pm 4.4\text{nm}$ to $54.2\pm 11.9\text{nm}$ of branches. Antibacterial activity against Propionibacterium acnes of gold nanostars was also investigated. Propionibacterium acnes is one of the main reasons causing acne vulgaris. The antibacterial test was evaluated by the plate count and well diffusion method. The results showed a significant effect that gold nanostars could be the prospective agent for replacing antibiotics in acne treatment.