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.
Highlights
Has been done in improving mixing performance in microfluidics-based flow synthesis of hollow silica materials
For the formation of submicrometer hollow silica spheres (smHSSs), firstly an interface of silica precursor in non-aqueous phase and catalyst in aqueous phase is needed where the hydrolysis of tetraethyl orthosilicate (TEOS) occurs, continuous condensation of hydrolyzed TEOS with mixing of the two reactant flows builds up the shell layer
We chose microfluidic spiral channel as: (1) with low Reynolds number (Re < ~2000), viscous-dominated laminar flows are common in microfluidic devices, which facilitates creating the interface of two reactant flows; and (2) in microfluidic spiral channels, mixing is largely enhanced with the introduction of chaotic advection due to the transverse Dean flow across the channel as a result of centrifugal effects[23]
Summary
Has been done in improving mixing performance in microfluidics-based flow synthesis of hollow silica materials. Even less work has been reported on the synthesis of multifunctional silica materials. Developing new mixing-enhanced microfluidic devices for the synthesis of hollow silica spheres, especially multifunctional ones integrated with other materials, is still a big challenge and in great demand. We demonstrate the synthesis of hollow silica spheres at submicrometer scale in a microfluidic spiral channel, which combines diffusion-limited reactions at the interface of two laminar flows near the inlets and does not require the generation of droplets, and enhanced instant mixing as the interfacial area of two miscible phases is stretched and extended across the microchannel because of transverse Dean flow effects. By increasing the flow rate to 400 μL/min, submicrometer hollow silica spheres (smHSSs) could be synthesized in less than one second. The simplicity and versatility of this method largely facilitate the fabrication of multifunctional smHSSs loaded with proteins, fluorescent dyes, quantum dots, and magnetic nanoparticles for diverse applications such as cell imaging, dye adsorption, and drug delivery
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