Asymmetrical Molecular Decoration of Gold Nanorods for Engineering of Shape-Controlled AuNR@Ag Core–Shell Nanostructures

Abstract

Gold−silver (Au@Ag) core−shell nanostructures have a stronger surface plasma response, wider absorption and scattering in the UV−vis−NIR region, and distinctive optical properties, which are widely explored in biosensors, information processing, photothermal therapy, and catalysis. Core−shell nanostructures are usually formed by the deposition of the second metal atoms onto the first core metal particles via the chemical wet method. The conventional approaches for the manipulation of the shape usually were done by homogeneous growth or etching of isotropic nanoparticles. Through in situ modification of the first metal core at the different locations, the different growth model of the second metal can be regulated to control the shapes of core−shell structures. Herein, we modified the gold nanorods (AuNRs) asymmetrically at the end and side parts using thiolated molecules to regulate the morphology of gold nanorod@silver (AuNR@Ag) core−shell nanoparticles. Interestingly, the obvious eccentric nanostructures of AuNR@Ag core−shell nanoparticles were obtained with the increase of the molecular weight of macromolecules modified at the end of AuNRs. Therefore the growth mode was adjusted from Frank−van der Merwe mode to Stranski−Krastanow mode. By changing the length of the hydrocarbon chain and functional groups of the small mercaptan molecules at the side of AuNRs, the silver shell exhibits selective growth at the side of the AuNRs, resulting in heterogeneous core−shell nanoparticles and various shapes of the AuNR@Ag core−shell. Our method opens up a new avenue toward preparing core−shell nanostructures with controlled shapes, and the obtained structures are promising in various applications.

Solvent Quality-Mediated Regioselective Modification of Gold Nanorods with Thiol-Terminated Polymers

“…Because of the coordination between Ag ions with N atoms, the silver shell only grew in the P4VP domain. , As-prepared Au@Ag NPs exhibited an olive-like shape, where the sidewall of AuNRs was covered with silver shell and the ends were exposed (Figure e–f). These bimetallic Au@Ag NPs may find applications in the surface-enhanced Raman spectrum and catalysis. − …”

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

“…CTAB molecules are unevenly distributed on the different crystalline surfaces of Au NRs due to the special geometrical shape of Au NRs . When the concentration of CTAB is reduced to a certain extent, thiol molecules can selectively replace the loose CTAB molecules at the NR ends. − The other modification approach is surface coating with organic molecules through electrostatic adsorption, hydrogen bonding, or coordination. We introduce several types of organic capping molecules below, including surfactants (other than CTAB), small molecules, synthetic polymers, and biomolecules.…”

Synthesis of Palladium Nanodendrites Using a Mixture of Cationic and Anionic Surfactants

“…The seed-mediated growth method is a versatile and efficient method for synthesizing high-quality metallic nanoparticles. , This method has some interesting features: (a) particle size and shape can be controlled, (b) the reaction rate is relatively fast when close to room temperature, (c) the experimental process is typically simple and inexpensive, and (d) core–shell particles can be synthesized. − In a typical seed-mediated growth synthesis, the nucleation of metallic crystal seeds starts with a rapidly occurring reduction reaction, resulting in a high concentration of tiny metallic seeds. Then, the seed solution is injected into a growth solution, which supplies the necessary reagents for the seeds to grow into larger nanoparticles. , This growth process can be repeated in multiple, short steps with new growth solutions for each step to grow the nanoparticles slowly, or the process can happen in one, more concentrated, growth solution over a longer period of time, through a process such as Ostwald ripening. , Generally, a metal salt, a reducing agent, and a capping agent are necessary in both seed and growth solutions .…”