Synthesis of Finely Controllable Sizes of Au Nanoparticles on a Silica Template and Their Nanozyme Properties

Abstract

The precise synthesis of fine-sized nanoparticles is critical for realizing the advantages of nanoparticles for various applications. We developed a technique for preparing finely controllable sizes of gold nanoparticles (Au NPs) on a silica template, using the seed-mediated growth and interval dropping methods. These Au NPs, embedded on silica nanospheres (SiO2@Au NPs), possess peroxidase-like activity as nanozymes and have several advantages over other nanoparticle-based nanozymes. We confirmed their peroxidase activity; in addition, factors affecting the activity were investigated by varying the reaction conditions, such as concentrations of tetramethyl benzidine and H2O2, pH, particle amount, reaction time, and termination time. We found that SiO2@Au NPs are highly stable under long-term storage and reusable for five cycles. Our study, therefore, provides a novel method for controlling the properties of nanoparticles and for developing nanoparticle-based nanozymes.

Synthesis of Gold-Platinum Core-Shell Nanoparticles Assembled on a Silica Template and Their Peroxidase Nanozyme Properties

“…The K m of SiO 2 @Au@Pt was higher than those of Au NPs (K m = 123 µM), SiO 2 @Au@Au NPs (Km = 60 µM), glucose oxidase-conjugated Au-attached SiO 2 microspheres (K m = 208 µM), MnO 2 NPs (K m = 83 µM), and latex-conjugated MnO 2 NPs (K m = 99 µM). The K m of SiO 2 @Au@Pt was lower than those of Au NPs-decorated porous silica microspheres (K m = 523 µM) and Prussian-blue-decorated latex NPs (K m = 2.19 mM) [ 55 ]. The V max of SiO 2 @Au@Pt was higher than that of SiO 2 @Au@Au (V max = 2.1 × 10 −10 M −1 ∙s −1 ), indicating that SiO 2 @Au@Pt oxidizes TMB at a faster rate than SiO 2 @Au@Au.…”

“…The peroxidase-like activity of SiO 2 @Au@Pt NPs synthesized with 100–400 μM Pt 2+ was estimated using a TMB assay. The SiO 2 @Au seeds showed very weak peroxidase-like activity because of the lack of spaces on the SiO 2 @Au NPs and the small Au NPs on the SiO 2 template, resulting an insufficient surface area for the catalytic reaction between the Au NPs and the TMB-H 2 O 2 mixture [ 55 ]. The UV-Vis absorption spectra of all SiO 2 @Au@Pt NPs showed an absorbance peak at 453 nm ( Figure 3 c–e), indicating that all of the SiO 2 @Au@Pt NPs had peroxidase-like activity that was dependent on the initial Pt 2+ concentration.…”

“…Au@Ag or Au NPs immobilized on SiO 2 NPs have been developed recently [ 54 , 55 , 56 , 57 , 58 ]. In these nanostructures, the SiO 2 NPs serve as a template and the metal NPs are introduced to the surface using the seed-mediated growth method.…”

“…Because of the SiO 2 core, the metal NPs assembled on SiO 2 nanostructures are cost-effective, more stable during surface modification, easily separatable from the reaction solution, aggregate less than fine metal NPs, and redisperse into solution with enhanced separation compared with single metal NPs. Furthermore, the effects of various synthesis factors on metal NPs assembled on SiO 2 have been studied using near-infrared surface enhanced Raman scattering nanoprobes for bioimaging [ 55 , 56 ]. However, research regarding the high peroxidase-like activity of the metal NPs assembled on SiO 2 is limited.…”

“…First, a suspension of Au seeds (approximately 2.5 nm) was prepared using tetrakis(hydroxymethyl)phosphonium chloride (THPC) and HAuCl 4 . Then, the Au seeds were mixed with aminated SiO 2 NPs (approximately 160 nm) overnight to obtain SiO 2 @Au seeds, as previously reported [ 54 , 55 , 57 , 58 , 62 , 63 , 64 ]. On the SiO 2 @Au seeds, the reduction of Pt 2+ to Pt(0) was directly induced using AA, a mild reducing agent, in the presence of polyvinylpyrrolidone (PVP).…”