Ultrafast Synthesis of Multifunctional Submicrometer Hollow Silica Spheres in Microfluidic Spiral Channels

Abstract

We demonstrate a facile and ultrafast approach for the synthesis of multifunctional submicrometer hollow silica spheres (smHSSs) using microfluidic spiral channels with enhanced mixing performance, introduced by the transverse Dean flows cross the channel as a result of centrifugal effects. Formation of smHSSs is initiated by the hydrolysis of tetraethyl orthosilicate (TEOS) at the interface of two laminar reactant flows. Complete mixing of the flows further facilitates the subsequent condensation of hydrolyzed TEOS, which builds up the shell layer of smHSSs. The average size of the as-synthesized smHSSs is 804.7 nm, and the thickness of the shell layer is ~20 nm. Multifunctional smHSSs integrated with proteins, fluorescent dyes, quantum dots, and magnetic nanoparticles can be further produced via this general platform. Their applications in cell imaging, organic dye adsorption, and drug delivery are examined.

Microfluidics for silica biomaterials synthesis: opportunities and challenges

“…The as-synthesized fluorescent silica particles can effectively interact with SK-BR-3 cancer cells with negligible cytotoxicity ( Figure 11C). 56 These preliminary results revealed the promising potential of silica bioimaging agents from microreactors. However, further studies are needed to demonstrate their practical applicability in the clinical settings.…”

“…3.1.2 Porous sphere-Laminar flow synthesis of porous silica spheres can be realized by the aid of surfactants (such as hexadecyltrimethylammonium salts 43,52,56 ) or polymer (such as polyacrylic acid 55 ). To prepare uniformly sized porous silica sphere, one feasible way is to separate nucleation and growth processes.…”

“…43 For the synthesis of hollow porous silica spheres, our research group first demonstrated the feasibility of spiral-shaped microreactor with one inlet containing silica precursor and the other surfactant in diluted ammonia ( Figure 4B). 56 Because of the transverse Dean flow effects, the reactants could achieve instantly complete mixing and hollow silica spheres could be obtained in less than one second. Relying on the hydrodynamic focusing micromixer, hollow silica spheres can also be produced in the presence of poly(acrylic acid) as template ( Figure 4C).…”

“…Microfluidics provides great opportunities for the synthesis of new silica bioimaging agents by either assembly 91,105,110 or sol-gel chemical reactions. 56 For the synthesis of efficient ultrasound imaging agent, droplet microreactors could easily assemble silica-coated CdSe/ZnS QDs nanoparticle on the surface of perfluorocarbon microbubbles via the electrostatic attraction between nanoparticles and microbubble shell. In vitro ultrasound images demonstrated that, compared to microbubbles alone, silica-QDs-incorporated microbubbles obviously improved the signal intensity on both contrast-specific imaging and B-mode imaging ( Figure 11A).…”

“…Compared to post-synthesis batch loading approach of drugs, 54,56,120 microfluidic approach permits one-step encapsulation of aqueous insoluble and aqueous soluble drugs during the formation of resultant silica-based biomaterials, which significantly simplifies the drug loading procedures. 111,122 To achieve sustained drug delivery, microfluidics can encapsulate drug-loaded thermally hydrocarbonized porous silicon (THCPSi) microparticles within solid lipid microparticles (SLMs).…”