Controlled synthesis of monodisperse gold nanorods with a small diameter of around 10 nm and largest plasmon wavelength of 1200 nm.

Gold nanorods have been widely used in various fields due to their tunable anisotropic localized surface plasmon resonance (SPR) property. The facile preparation of gold nanorods with a tunable SPR wavelength extending to a near-infrared window, and at the same time, a relatively small particle size for facilitating applications especially in the biomedical field is of great value yet highly challenging. In this work, a new reducing agent, 1,6-dihydroxynaphthalene, is proposed for the synthesis of gold nanorods. The results indicate that gold nanorods with good monodispersity, high shape yield, maximum SPR wavelength of 1200 nm, and especially small diameter of around 10 nm can be acquired simultaneously. In terms of spectral and size controls, by respectively varying the experimental parameters including the amount of silver ions, reducing agents, and gold seeds not only can a good linear correlation be acquired corresponding to a SPR wavelength ranging from around 600 nm to 1200 nm, but a regular change in the particle diameter from 10.5 nm to 7.5 nm could also be observed. The structural and morphological evolutions of the particle for each changed parameter were carefully studied, and insights were gained into the growth mechanism based on the detailed analysis of particle evolution at a specific stage of the growth process.

Spectrum and size controllable synthesis of high-quality gold nanorods using 1,7-dihydroxynaphthalene as a reducing agent.

The spectrum and size controllable synthesis of gold nanorods is of great value for their widely applicable aspect ratio dependence of anisotropic surface plasmon resonance. Herein, 1,7-dihydroxynaphthalene with a relatively strong reducibility is proposed as a reducing agent for the controllable synthesis of gold nanorods. The result indicated that gold nanorods with high monodispersity, high shape yield, relatively small diameters, and maximum plasmon resonance wavelength of above 1000 nm can be acquired. More importantly, by virtue of the reducing agent used, fine and precise controls over the plasmon wavelength and diameter of the rod can be achieved via changes in experimental conditions. In particular, increases in the concentration of both silver ions and cetyltrimethylammonium bromide (CTAB) can increase the plasmon wavelength from around 600 nm to 1000 nm but respectively show a decreased diameter with the smallest value of around 14.3 nm and a mildly increased diameter from around 9.0 nm to 14.3 nm; moreover, increasing the concentration of reducing agents and gold seeds can simultaneously cause decreases in the plasmon wavelength from around 1000 nm to 800 nm and the diameters from around 14.3 nm to 9.0 and 7.3 nm, respectively. This powerful and efficient method of controllable synthesis of AuNRs could be valuable and attractive for the application of the as-obtained particles.

High-yield synthesis of monodisperse gold nanorods with a tunable plasmon wavelength using 3-aminophenol as the reducing agent.

Facile synthesis of high quality gold nanorods (AuNRs) with a tunable size is of great value for applications of AuNRs in various fields and for the study of the growth mechanism of such anisotropic nanostructures. However, limitations usually exist in a specific synthetic protocol. In this work, using 3-aminophenol as the reducing agent, we present a AuNR synthetic strategy with an excellent comprehensive performance, which includes an exceptional monodispersity, a AuNR shape purity of around 99%, a conversion ratio of the gold precursor of about 91%, and an easily tuned longitudinal surface plasmon resonance wavelength ranging from 580 to ∼1050 nm. Studies on the impacts of the experimental parameters including silver ions, gold seeds, reducing agent, and cetyltrimethylammonium bromide (CTAB) revealed a profound recognition of the significant effect of the reductive atmosphere, in synergy with other parameters, in directing the growth and structural evolution of the gold seeds, thus deeply affecting the size, shape yield, monodispersity, and morphology of the final structure. These results could be immensely useful for the application and revelation of the growth mechanism of AuNRs.