Tunability and stability of gold nanoparticles obtained from chloroauric acid and sodium thiosulfate reaction
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NANO EXPRESS
Open Access
Tunability and stability of gold nanoparticles obtained from chloroauric acid and sodium thiosulfate reaction Guandong Zhang1, Jacek B Jasinski2, Justin Lee Howell1, Dhruvinkumar Patel1, Dennis P Stephens1 and Andre M Gobin1*
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. Keywords: gold nanoparticles, gold colloid, gold nanoplates, near-infrared absorption, surface plasmon resonance, sodium thiosulfate, core-shell structure
Background Metal nanoparticles are one of the basic building blocks of nanotechnology. 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. Specifically, 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 [4-6]. These applications have sparked great interest in the development of synthetic methods for preparing different gold-based nanostructures. The anisotropy in nanoparticle shape offers high * Correspondence: [email protected] 1 Bioengineering Department, J.B. Speed School of Engineering, Room 411, Lutz Hall, Belknap campus, Louisville, KY 40292, USA Full list of author information is available at the end of the article
near-infrared absorption and improved Raman scattering [7]. Based on Mie scattering theory, shifts in the surface plasmon resonance (SPR) [8] occur when the particles deviate from spherical geometry. Non-spherical gold nanoparticles present multiple absorption bands correlating with their multip
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