Gram‐Scale Synthesis of Isolated Monodisperse Gold Nanorods

Abstract

Although gold nanorods (AuNRs) have strong potential applications in nanotechnology, plasmonics, and sensing, the scale‐up synthesis of isolated AuNRs in gram quantities remains a challenge. Nearly all previously reported methods produce aqueous solutions of cetyltrimethylammonium bromide (CTAB)‐coated AuNRs in milligram quantities with yields of approximately 20–30 % in terms of AuI to Au0 conversion. In addition, it is difficult to remove the CTAB bilayer from the surface of AuNRs and yet make them soluble and functionalized for further processing and chemical modification. This report describes the synthesis of monodisperse functionalized AuNRs (standard deviation, σ≈5 %) in gram quantities. Our approach involved increasing the concentration of HAuCl4⋅3 H2O in the growth solution to produce larger quantities of starting AuNRs and further reducing the remaining AuI ions onto the surface of AuNRs. The slow and controlled addition of ascorbic acid as a reducing agent continued the conversion of AuI into Au0 (through a disproportionation reaction) onto the surface of the nanorods, which maintained their uniform morphology without creating any unwanted impurities of various shapes. In addition, this approach significantly narrowed the size distribution owing to continuous growth of the partially grown AuNRs during the initial stage of the synthesis. To isolate a 1 g quantity of the AuNRs and to make them functionalized for further chemical reactions, a ligand‐exchange approach was utilized, in which the CTAB surfactant was replaced with 4‐mercaptophenol. The thiol group from 4‐mercaptophenol formed a covalent bond with the surface of the AuNRs, leaving free functional OH groups available for further chemical coupling reactions. For the ligand‐exchange process, a concentrated solution of 4‐mercaptophenol in tetrahydrofuran solution was introduced into the AuNRs solution. Pure AuNRs functionalized with 4‐mercaptophenol were isolated by dispersion and rinsing with an excess amount of THF, followed by centrifugation.

Gold Nanorods for LSPR Biosensing: Synthesis, Coating by Silica, and Bioanalytical Applications

“…One can also mention here the work of Khanal and Zubarev who reported the successful gram-scale synthesis of AuNRs using the El-Sayed protocol by (i) increasing the concentration of gold by a factor of 2; (ii) increasing the volume of aqueous solution by a factor of 600 (from 10 mL to 6 L), and (iii) increasing the yield in reduced gold to ca. 100 by slow addition of AA after the first growth step [ 65 ].…”

Delivery of drugs, proteins, and nucleic acids using inorganic nanoparticles

“…The optical responsiveness of gold nanomaterials has garnered especial interest in gold nanorods (AuNRs), elongated Au-based nanoscale materials with optical properties that can be finely tuned through the aspect ratio of the rods [161,162,163]. Upon wavelength specific irradiation, AuNRs generate heat, potentially providing for localized payload release [164,165,166].…”

Synthesis of Uniform Gold Nanorods with Large Width to Realize Ultralow SERS Detection

“…For classic CTSG of Au NRs, the [HAuCl 4 ] in the growth solution needs to be reasonably high, usually 0.39 mM or above, due to low utilization and a larger amount of active gold species remains after the Au NRs are formed, which cause in corrosion of the resulting Au NRs if they are still kept in the original reaction solutions without necessary purification treatments. [43,52,53] Thanks to the high utilization of HAuCl 4 in the presence of heptanol, HA-CTSG method enables us to produce Au NRs at the [HAuCl 4 ] as low as 0.024 mM (Figure 3a and Table S15). In contrast, no Au NRs can be produced via classic CTSG.…”