Ultrasmall Au–Ag Alloy Nanoparticles: Protein-Directed Synthesis, Biocompatibility, and X-ray Computed Tomography Imaging

The ultrasmall sizes of nanoparticles have attracted significant attention for potential applications in the fields of catalysis and nanomedicine. Herein, we reported on the green preparation and X-ray computed tomography (CT) imaging of ultrasmall bimetallic bovine serum albumin-directed gold–silver (Au–Ag@BSA) nanoparticles (2–4 nm) using BSA as a stabilizing and template-directed agent. Further, the effects of synthesis conditions were systematically explored to prepare products by adjusting the different molar ratios of Au/Ag. The resulting Au–Ag@BSA nanoparticles exhibited the spherical shape, well-dispersed ability, as well as long-term room-temperature stability. The cytotoxicity effects of Au–Ag@BSA nanoparticles on A549 and MCF-7 cells were compared with those of individual Ag nanoparticles, and the results indicated a lower cytotoxicity effect by Au–Ag@BSA nanoparticles. Furthermore, the in vivo toxicity of Au–Ag@BSA nanoparticles was investigated in the early stage zebrafish embryos. The results indicate that there are not any obvious changes of survival and hatching percentages at multiple growth stages (4–120 hpf) even with a high level of Au–Ag@BSA nanoparticles (up to 80 mM), revealing good biocompatibility. Interestingly, a rational design of the Au/Ag molar ratio (3:2) surprisingly possessed enhanced CT performance compared to the performance of the Au nanoparticles and iohexol. Accordingly, this study highlights a new prospect in the green preparation of ultrasmall alloy nanomaterials with good biocompatibility and will be of great interest in developing CT contrast agent, catalyst, as well as drug delivery carrier.