Size Control of Silver-Core/Silica-Shell Nanoparticles Fabricated by Laser-Ablation-Assisted Chemical Reduction

Abstract

Aqueous colloidal silver nanoparticles have substantial potential in biological application as markers and antibacterial agents and in surface-enhanced Raman spectroscopy applications. A simple method of fabrication and encapsulation into an inert shell is of great importance today to make their use ubiquitous. Here we show that colloids of silver-core/silica-shell nanoparticles can be easily fabricated by a laser-ablation-assisted chemical reduction method and their sizes can be tuned in the range of 2.5 to 6.3 nm by simply choosing a proper water-ethanol proportion. The produced silver nanoparticles possess a porous amorphous silica shell that increases the inertness and stability of colloids, which decreases their toxicity compared with those without silica. The presence of a thin 2 to 3 nm silica shell was proved by EDX mapping. The small sizes of nanoparticles achieved by this method were analyzed using optical techniques, and they show typical photoluminescence in the UV-vis range that shifts toward higher energies with decreasing size.

One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

“…Recently, the approaches of PLAL and laser photochemical reduction have been combined into a single process through ablation of a solid target either immersed in or subsequently exposed to metal salt solution, in what is termed reactive laser ablation in liquid (RLAL) [10,[45][46][47][48][49][50][51][52]. RLAL has been widely used to generate metal-silica nanostructures, including Si/M (M = Ag, Au, Pd, Pt) core/shell NPs [47], Ag-core/silica-shell NPs [48], and large silica particles decorated with Au or Ag NPs [49]. While these RLAL reports have demonstrated the generation of hybrid semiconductor-metal nanocomposite materials in a single step, the metal-silica products are too large for catalysis applications such as CO oxidation that typically requires sub-5 nm metal NPs [53][54][55][56].…”

“…In this work, we report a RLAL approach where a Si wafer immersed in a KAuCl 4 solution is ablated using sub-50 femtosecond (fs) laser pulses (fs-RLAL), producing significantly smaller silica-Au nanostructures than in previous reports using nanosecond lasers [47][48][49]. Using a high surface area support such as silica is commonly used to stabilize metal nanoparticles during catalytic reactions [60,61].…”

Assisted laser ablation: silver/gold nanostructures coated with silica

“…There are different pathways for synthesizing nanoparticles (NPs); however, it is a challenge for all of them to improve the control of physical properties of the nanostructures, since their behavior will largely depend on their characteristics (Fojtik et al 1993;Jiménez et al 2004;Pyatenko et al 2004;Popovici et al 2006;Pyatenko et al 2007;Jiménez et al 2008;Cobley et al 2009;Jiménez et al 2010;González-Castillo et al 2015;Ermakov et al 2017). In 2008, Jiménez et al demonstrated a novel hybrid physicalchemical method based on a chemical reaction assisted by laser ablation (Jiménez et al 2008).…”

“…This method, assisted laser ablation (ALA), is basically a chemical synthesis (redox) where one of the reactants (silicon) is supplied in nanometer dimensions by laser ablation (Jiménez et al 2010). The laser ablation method is a powerful technique for producing nanostructured materials in different environments (Fojtik et al 1993;Jiménez et al 2004;Pyatenko et al 2004;Popovici et al 2006;Ermakov et al 2017). Recently, González-Castillo et al reported the synthesis of silver (Ag) NPs by ALA in two steps (González-Castillo et al 2015).…”

“…In the second step, the silver salt (AgNO 3 ) was added. In a subsequent work, (Ermakov et al 2017) SiO 2 H 2 isomers on the silica NP surface (McCarthy and Gauss 2016), produced during the vigorous oxidation of silicon NPs (laser ablation), were proposed as possible reducing agents of the silver ions. The silica coatings provide inertness and high dispersibility, which has enabled their use in numerous applications (Rodriguez et al 2005;Abderrafi et al 2012;Jimenez-Villar et al 2013, 2017.…”