Tunability and stability of gold nanoparticles obtained from chloroauric acid and sodium thiosulfate reaction
1 Bioengineering Department, J.B. Speed School of Engineering, Room 411, Lutz Hall, Belknap campus, Louisville, KY, 40292, USA
2 Conn Center for Renewable Energy Research, J.B. Speed School of Engineering, University of Louisville, Louisville, KY, 40292, USA
Nanoscale Research Letters 2012, 7:337 doi:10.1186/1556-276X-7-337Published: 22 June 2012
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.