Engineering miniature gold nanorods with tailorable plasmonic wavelength in NIR region via ternary surfactants mediated growth

Plasmonic nanoparticles are endowed profound capability for sensing, biomedicine, and cancer therapy. However, the inaccessibly adjustable wavelength in near infrared (NIR) region window and size limit for the particles penetration in tumor strongly hinder their developments. Miniature gold nanorods (mini-Au NRs) with diameter less than 12 nm can effectively address this challenge due to the tiny size and tailorable NIR absorption. Herein, we adopt ternary surfactants (hexadecyl trimethyl ammonium bromide (CTAB), sodium oleate (NaOL), and sodium salicylate (NaSal)) mediated growth strategy to precisely synthesize miniature Au NRs under micelle space-confinement. Importantly, the selectively dense accumulation of ternary surfactants can efficiently improve the micellar stacking parameters (p) and lower micellar free energy (F), further tends to achieve the formation of Au NRs with tiny diameter and high purity. Compared with that of conventional methods, the purity of mini-Au NRs up to 100% can be dramatically improved via varying the relative concentration of ternary surfactants. The diameter of Au NRs can be dynamically controlled to 6, 8, and 11 nm through regulating the concentration of silver nitrate and the mole ratio of ternary surfactants. Such ternary surfactants system is favorable for the aging of tiny Au NRs, and further enables the aspect ratio-tunable in the region from 2.70 to 7.32, as well as tailorable plasmonic wavelength in wide NIR window from 700 to 1,147 nm. Therefore, our findings shed a light on the precise preparation of small sized plasmonic nanoparticles and pave the way to applications in biomedicine, imaging, and cancer therapy.