In Situ Growth of Hollow Gold–Silver Nanoshells within Porous Silica Offers Tunable Plasmonic Extinctions and Enhanced Colloidal Stability

Abstract

Porous silica-coated hollow gold-silver nanoshells were successfully synthesized utilizing a procedure where the porous silica shell was produced prior to the transformation of the metallic core, providing enhanced control over the structure/composition of the bimetallic hollow core. By varying the reaction time and the precise amount of gold salt solution added to a porous silica-coated silver-core template solution, composite nanoparticles were tailored to reveal a readily tunable surface plasmon resonance that could be centered across the visible and near-IR spectral regions (∼445-800 nm). Characterization by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed that the synthetic methodology afforded particles having uniform composition, size, and shape. The optical properties were evaluated by absorption/extinction spectroscopy. The stability of colloidal solutions of our composite nanoparticles as a function of pH was also investigated, revealing that the nanoshells remain intact over a wide range of conditions (i.e., pH 2-10). The facile tunability, enhanced stability, and relatively small diameter of these composite particles (∼110 nm) makes them promising candidates for use in tumor ablation or as photothermal drug-delivery agents.

Bimetallic Nanoparticles: Enhanced Magnetic and Optical Properties for Emerging Biological Applications

“…This technique was utilized to synthesize core-shell nanoparticles by Mancier et al for the generation of Cu/Ag nanoparticles [101]. Similarly, Li and co-workers combined galvanic replacement and diffusion through a protective porous silica shell to synthesize SiO2-coated hollow Ag-Au nanoparticles for use as stable plasmonic agents for NIR activation [102].…”

Surface modification with zwitterionic cysteine betaine for nanoshell-assisted near-infrared plasmonic hyperthermia

“…This procedure generated monodispersed silver nanoparticles, where the size could be adjusted from 40 nm to 100 nm, depending on the concentration of the reactants. For the synthesis of hollow gold-silver nanoshells as described in previous studies [15,40,41], 0.050 g of K 2 CO 3 was added to 200 mL of purified water, which was then injected into 4 mL of 1%…”

“…More specifically, novel metal nanoparticles have been employed as powerful agents for PTT because of their robust photostability and strong optical response via the surface plasmon resonance (SPR). A variety of plasmonic nanostructures including nanospheres, [12,13] nanoshells [14,15], nanorods [16,17], and nanocages [18], have been developed that respond to wavelengths in the visible and near infrared (NIR) regions. In the PTT applications, in addition to a strong extinction, the nanoparticle agents should possess additional properties, such as nontoxicity, long-term colloidal stability, high biocompatibility, and facile functionalization [19].…”

The Development of Smart, Multi-Responsive Core@Shell Composite Nanoparticles

“…After coating with silica, the metal's plasmon peak red-shifted to ~540 nm. This is because the refractive index of silica (n = 1.52) is slightly higher than that of water (n = 1.31), the solvent used to suspend the nanoparticles for collecting spectroscopic data [106]. The optical intensity of these Au@SiO 2 NPs was increased correspondingly when thicker silica shells were created.…”