Characterization of Conventional One-Step Sodium Thiosulfate Facilitated Gold Nanoparticle Synthesis

Abstract

Gold-gold sulfide nanoparticles are of interest for drug delivery, biomedical imaging, and photothermal therapy applications due to a facile synthesis method resulting in small particles with high near-infrared (NIR) absorption efficiency. Previous studies suggest that the NIR sensitivity of these nanoparticles was due to hexagonally shaped metal-coated dielectric nanoparticles that consist of a gold sulfide core and gold shell. Here, we illustrate that the conventional synthesis procedure results in the formation of polydisperse samples of icosahedral gold particles, gold nanoplates, and small gold spheres. Importantly, through compositional analysis, via UV/vis absorption spectrophotometry, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS), we show that all of the nanoparticles exhibit identical face center cubic (FCC) gold crystalline structures, thus suggesting that sulfide is not present in the final fabricated nanoparticles. We show that icosahedrally shaped nanoparticles result in a blue-shifted absorbance, with a peak in the visible range. Alternatively, the nanoplate nanoparticles result in the characteristic NIR absorbance peak. Thus, we report that the NIR-contributing species in conventional gold-gold sulfide formulations are nanoplates that are comprised entirely of gold. Furthermore, polydisperse gold nanoparticle samples produced by the traditional one-step reduction of HAuCl4 by sodium thiosulfate show increased in vitro toxicity, compared to isolated and more homogeneous constituent samples. This result exemplifies the importance of developing monodisperse nanoparticle formulations that are well characterized in order to expedite the development of clinically beneficial nanomaterials.

The surface chemistry of near-infrared resonant gold nanotriangles obtained via thiosulfate synthesis

“…In order to assess the influence of the AuNPs treatments on cell adhesion and proliferation, 5 × 10 5 cells were seeded in 6 multi-well plate and grown at 37°C in 5% CO 2 humid atmosphere in CCM. After 24 h medium was replaced by aliquots with different final concentrations of AuNPs (25,50,100,200, 500 µM of gold) and under these conditions cells were cultured during 24 h. Additionally, BALB/c 3T3 cell cultures without AuNPs were also evaluated and used as control. After exposure time, cells were washed with PBS, adherent cells were stained with AO dye (Sigma) and immediately examined by epifluorescence microscopy (Olympus BX51) equipped with appropriate filter connected to an Olympus DP71 color video camera.…”

“…An interesting strategy to overcome this is the use of sulfur compounds as reducing agents of Au(III) ions in aqueous solutions. Sulfide and thiosulfate have been both used to obtain truncated AuNTs with intense absorption in the so-called NIR-I biological window (around 800 nm) [22][23][24][25][26][27]. However, due to the presence of spherical AuNPs in addition to the AuNTs, there has been some controversy about the nanoparticles responsible for NIR absorbance [28][29][30][31][32].…”

Core-shell of FePt@SiO2-Au magnetic nanoparticles for rapid SERS detection

“…The most common and well investigated metallic nanoparticles, gold nanoparticles hold particularly interesting characteristics. Gold nanoparticles were applied in the significant place in medicine, material sciences, as well as diagnostics for their unique optical and physiochemical properties [ 1 , 20 – 25 ]. Their facile synthesis and bio-conjugation procedures, along with its unique surface plasmon properties, made gold nanoparticles practicable in labs without expensive or sophisticated equipment [ 26 – 28 ].…”

Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

“…Appropriate centrifuging programme allowed to remove most of the colloidal gold from the solution, SI Figure S3, S4. Other methods like density gradient centrifugation , or microfiltration or flocculation can be also useful to achieve the desired separation.…”