Abstract
In the quest for producing an effective, clinically relevant therapeutic agent, scalability, repeatability, and stability are paramount. In this paper, gold nanoparticles (GNPs) with precisely controlled near-infrared (NIR) absorption are synthesized by a single-step reaction of HAuCl4 and Na2S2O3 without assistance of additional templates, capping reagents, or seeds. The anisotropy in the shape of gold nanoparticles offers high NIR absorption, making it therapeutically relevant. The synthesized products consist of GNPs with different shapes and sizes, including small spherical colloid gold particles and non-spherical gold crystals. The NIR absorption wavelengths and particle size increase with increasing molar ratio of HAuCl4/Na2S2O3. Non-spherical gold particles can be further purified and separated by centrifugation to improve the NIR-absorbing fraction of particles. In-depth studies reveal that GNPs with good structural and optical stability only form in a certain range of the HAuCl4/Na2S2O3 molar ratio, whereas higher molar ratios result in unstable GNPs, which lose their NIR absorption peak due to decomposition and reassembly via Ostwald ripening. Tuning the optical absorption of the gold nanoparticles in the NIR regime via a robust and repeatable method will improve many applications requiring large quantities of desired NIR-absorbing nanoparticles.
Highlights
Metal nanoparticles are one of the basic building blocks of nanotechnology
Sodium thiosulfate works as a complexing agent
In summary, we report on a convenient synthesis process to precisely control the optical absorption within the near infrared (NIR) region and established the suitable range of concentrations to allow stable nanoparticle formation
Summary
Gold nanoparticles (GNPs) have attracted enormous attention in chemistry, biomedicine, and electronics due to their very small size, oxide-free surfaces, bio-conjugation properties, good biocompatibility, and unique optical properties Because of their optical activity in the near infrared (NIR), GNPs are extensively utilized in immunoassays [1,2], drug delivery systems [3] as well as imaging, detection, and thermal therapy of cancer [4,5,6]. Na2S may convert to different compounds, and sodium thiosulfate is one of the final compounds producing GNPs [20] These findings encouraged us to attempt to reveal the key factor that dominates the nanostructure formation and the stability of the GNPs in the HAuCl4/Na2S2O3 reaction. The instability of the GNPs is affected by the reaction conditions, resulting in the diversification of the nanostructures
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