Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

Abstract

1wileyonlinelibrary.com www.particle-journal.com www. MaterialsViews.com Gold nanoshells with tunable surface plasmon resonances are a promising material for optical and biomedical applications. They are produced through seed-mediated growth, in which gold nanoparticles (AuNPs) are seeded on the core particle surface followed by growth of the gold seeds into a shell. However, synthetic gold nanoshell production is typically a multistep, timeconsuming batch-type process, and a simple and scalable process remains a challenge. In the present study, a continuous fl ow process for the seedmediated growth of silica-gold nanoshells is established by exploiting the excellent mixing performance of a microreactor. In the AuNP-seeding step, the reduction of gold ions in the presence of core particles in the microreactor enables the one-step fl ow synthesis of gold-decorated silica particles through heterogeneous nucleation. Flow shell growth is also realized using the microreactor by selecting an appropriate reducing agent. Because self-nucleation in the bulk solution phase is suppressed in the microreactor system, no washing is needed after each step, thus enabling the connection of the microreactors for the seeding and shell growth steps into a sequential fl ow process to synthesize gold nanoshells. The established system is simple and robust, thus making it a promising technology for producing gold nanoshells in an industrial setting.polymer particles, are particularly attractive because of their unique optical and chemical properties, which allow visible and near-infrared light to be absorbed and converted into heat with high effi ciency, and absorption peaks can be tuned by the ratio of core size to shell thickness. The photothermal conversion characteristics can be advantageous for biomedical applications, such as photoacoustic imaging, [ 8 ] photothermal therapy, [ 9 ] sensing, [ 10 ] and gene silencing, [ 11 ] as well as solar energy applications. [ 12 ] The present study focuses on the synthesis of silica-gold core-shell particles (referred to as gold nanoshells). A typical synthetic method is seed-mediated growth, which was originally proposed by Halas and co-workers; [ 13 ] this method consists of three steps: surface modifi cation of the core silica particles, gold nanoparticle (AuNP) decoration of the modifi ed silica surface as "seeds," and growth of the AuNP seeds into a shell through the reduction of gold ions. Although this method allows for better control of the shell thickness, the preparation process is rather time consuming, taking days to complete. The bottleneck step is the AuNP seeding process, in which AuNPs are separately prepared by the reduction of gold ions, [ 14 ] aged for a certain period, ranging from several days to 2 weeks, [ 15 ] and then mixed with a suspension of surface-modifi ed silica particles to be adsorbed on the modifi ed silica surface due to the electrostatic attraction between the negatively charged AuNPs and the positively charged modifi ed silica surface. This process is f...

Synthesis and Surface Engineering of Inorganic Nanomaterials Based on Microfluidic Technology

“…Meanwhile, core-shell structured SiO 2 -Au nanoparticles were synthesized by using a simple and scalable microstructure mixer ( Figure 2 d) [ 88 ]. Similarly, silica nanocomposites modified by gold nanoparticles have been synthesized by using a central collision microreactor [ 89 ]. Moreover, TiO 2 -SiO 2 , Fe 3 O 4 -SiO 2 -Pt, and Co 3 O 4 -SiO 2 nanoparticles have also been fabricated by microfluidic technology [ 31 , 90 , 91 , 92 ].…”

Microfluidics for silica biomaterials synthesis: opportunities and challenges

“…This enables the coupling of seeding and shell growth into a sequential flow in microreactors to synthesize core-shell SiO 2 -Au nanocomposites through commercial slit interdigital microstructured mixer ( Figure 6C) or central collision-type microreactor ( Figure 6D). 47,50 Similar multistep nucleationcontrolled growth method can be also employed to synthesize TiO 2 -SiO 2 ( Figure 6E), 51 Fe 3 O 4 -SiO 2 -Pt ( Figure 6F), 48 and Co 3 O 4 -SiO 2 nanocomposites. 53 Our recent studies first demonstrated the flexibility of two-inlets spiral-shaped microreactors in the synthesis of anisotropic multifunctional hierarchical structures.…”

“…(D) Sequential flow synthesis of gold-coated silica particles in the central collision-type microreactor. Reproduced with permission from ref 50. (E) Controlled growth of silica-titania hybrid functional nanoparticles through a multistep microfluidic approach.…”

Protective Filtration for Microfluidic Nanoparticle Precipitation for Pharmaceutical Applications

“…Work on microfluidic mixing has contributed significantly to enabling the synthesis of nanoparticles with defined properties by antisolvent precipitation. Devices which rely on staggered herringbone mixers 7–10, flow focusing 11–14, multilamination 15, impinging jets 16–19, single droplet formation 20, Taylor flows 21, 22, or splitting the streams and recombining them to minimize the diffusion length 23, 24 have been described. Some groups added additional external power to intensify the mixing process, e.g., by using small rotors 25 or ultrasound 26–28.…”