Ask an Expert: I see some dogbone shaped gold nanoparticles under TEM. Will this cause any issues?
The formation of "dog bones" or other shapes such as "dumbbells" or "peanut shaped" particles in a gold nanoparticle solution may be a quality control issue and can be attributed to a number of factors.
In a surfactant based-seed mediated gold nanorod synthesis, the anisotropic shape of gold is thought to be controlled by a surfactant micelle (CTAB) acting as a template for directional growth of crystalline gold. It is thought that CTAB preferentially binds to the {110} facet (the cylindrical portion of the nanorod) over the {111} facet (the ends of the nanorod). The addition of a reducing agent (normally ascorbic acid) to a solution of gold salt containing CTAB capped seeds causes those seeds to grow along the {110} plane as the reducing agent reduces gold salt onto them, thus forming rods.
If the pH of the growth solution, temperature of the reaction, or concentration of the reducing agent are too high, the synthesis reaction rate can increase causing an undesired gold growth pattern at the ends of the nanorods (1). This uneven pattern of growth is likely caused by the fact that the surfactant does not guard the ends of the nanorods nearly as well as it does along the length, thus creating "dog bones" (2).
At NanoHybrids, we tackle this potential problem by carefully monitoring our synthesis to control rod thickness, length and shape. Additionally, every batch is inspected under TEM to ensure shape and size monodispersity.
References:
(1) pH-tuned synthesis of gold nanostructures from gold nanorods with different aspect ratios. Wang et al, Nanotechnology 16-11 (2005).
(2) Fine-Tuning the Shape of Gold Nanorods. Gou et.al, Chemistry of Materials 17-14 (2005).
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Our gold nanorod products:
CTAB-stabilized and PEGylated Gold NanoRods
