Post-synthesis heating, a key step to tune the LPR band of gold nanorods covered with CTAB or embedded in a silica shell

Abstract

The transitioning of nanotechnology from laboratory to industrial-scale manufacturing poses various challenges in nanoparticle realization. From this perspective, beside the conventional synthetic procedure, based on the seed-mediated growth approach, a reshaping thermal strategy has been investigated to improve the control on gold nanorods aspect ratio, with the aim to point out a potential and encouraging way to better manage the scalability and reproducibility of nanoparticles. For this purpose, nanorods covered with CTAB and nanorods enclosed within a silica shell of tuned thickness have been synthesized and submitted to a post-thermal treatment at various temperatures, up to 300 °C for CTAB recovered gold nanorods (AuNR@CTAB), and up to 500 °C for silica-shell embedded gold nanorods (AuNR@SiO2). For AuNR@CTAB, through accurate temperature control, the longitudinal plasmonic band can be moved very close to the transversal one upon slight reduction of their length. Instead, for AuNR@SiO2, owing to the fully inorganic shell, a higher temperature of treatment can be reached leading to the possibility of reshaping the nanorods into spheres without the observation of any by-products.

Triphenylphosphonium-Functionalized Gold Nanorod/Zinc Oxide Core–Shell Nanocomposites for Mitochondrial-Targeted Phototherapy

“…The GNR@ZnO core–shell nanocomposites were heated at various temperatures (200, 250, 300, and 400 °C), demonstrating a significant blue shift of the LSPR peak from 200 to 400 °C. By increasing the calcination temperature, the average length of the GNR core significantly decreased in the LSPR peak, as confirmed by morphological and optical characterization [ 29 ]. After conjugation with CTPP, the UV–vis absorption spectra of the CTPP-GNR@ZnO core–shell nanocomposites revealed a distinctive CTPP peak at 265 nm and a significant LSPR peak at 760 nm, suggesting that the mitochondrial-targeting CTPP molecule was efficiently conjugated on the surface of the GNR@ZnO core–shell nanocomposites, which is a highly efficient NIR phototherapy agent owing to its highly efficient capacity to generate photothermal heat and ROS [ 49 ].…”

“…GNRs are significantly small, approximately 85 nm in length and 20 nm in width, and demonstrate good optical tunability by controlling the aspect ratio (AR, length/width) of the NPs [ 27 ]. In addition to the seed-mediated growth method as a chemical strategy, physical approaches based on thermal and ultrafast laser-induced heating have also been suggested to modify the morphology of calcinated GNRs [ 28 , 29 ]. Therefore, protecting GNRs from heat-induced shape deformation is essential for effectively using them in particular applications including PTT [ 29 ].…”

“…In addition to the seed-mediated growth method as a chemical strategy, physical approaches based on thermal and ultrafast laser-induced heating have also been suggested to modify the morphology of calcinated GNRs [ 28 , 29 ]. Therefore, protecting GNRs from heat-induced shape deformation is essential for effectively using them in particular applications including PTT [ 29 ]. Zinc (Zn) is a trace element present in the hard tissues of teeth, muscles, bones, and skin [ 30 ].…”

Light-Induced Clusterization of Gold Nanoparticles: A New Photo-Triggered Antibacterial against E. coli Proliferation

“…In fact, within seconds, a layer of gold appeared on the surface of the colloidal solution under irradiation. Upon interrupting the irradiation and shaking the sample, the layer of gold disappeared; this phenomenon, induced by high-power laser irradiation, is widely reported in the literature [ 44 , 71 , 85 , 86 ].…”