Key Factors Affecting the Reproducibility of Synthesis and Growth Mechanism of Near-Infrared Absorbing Hollow Gold Nanospheres

Abstract

Hollow gold nanospheres (HGNs) with nearinfrared (NIR) surface plasmon resonance (SPR) absorption are highly desired for many applications including photothermal ablation therapy (PTA) of cancer; however, they are challenging to synthesize at relevant resonant wavelengths in a reproducible manner. In this work, we have systematically varied the reaction parameters to determine the origin of the irreproducibility of synthesis. This allows for much finer control of the synthesis, including homogeneous NIR absorbing HGNs that were characterized using UV−vis spectroscopy and electron microscopy (EM) techniques. We have found that cobalt seed particle growth time plays a more critical role than previously realized and is one of the most important parameters for high synthetic reproducibility. The results also provide new insight into the mechanism of cobalt seed and HGN growth, which further aids the successful synthesis of high quality HGNs with strong and tunable NIR SPR absorption.

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…HGNs are comprised of a hollow, solvent filled dielectric core and a polycrystalline gold shell [66,[75][76][77]. Both the core width and shell thickness can be tuned through synthesis to produce a range of overall diameters (20-125 nm) and aspect ratios.…”

“…Another effort focused on improving the synthetic reproducibility of NIR absorbing HGNs has been reported [77]. In this work an emphasis was placed on not only gaining control of the cobalt NP growth in order to maximize the size of the template but also on separating the nucleation and growth phases of the growing Co NPs.…”

“…In this work an emphasis was placed on not only gaining control of the cobalt NP growth in order to maximize the size of the template but also on separating the nucleation and growth phases of the growing Co NPs. This was achieved by optimizing reagent concentrations, and evaluating the kinetics of the cobalt nanoparticle growth [77].…”

“…This ensures an early saturation point is achieved and precursors will only deposit on existing nuclei [113]. It was found that the addition of citric acid, which acts as a scavenging agent for excess borohydride, shortened the hydrolysis time leading to a uniform growth period for the evenly reduced cobalt seeds [77].…”

“…For this reason a time course study to determine the optimal incubation period between the reduction step and galvanic replacement step was used to determine if the reaction time could be shortened to prevent potential Co oxidation [77].…”