On-chip synthesis of functional nanomaterials

Based on the special merits of microfluidics, such as high throughput, low samples consumption, high flexibility, low cost, automation capability, and enhanced spatio-temporal control, we developed a straightforward and general microreactor platform to produce micro-/nanostructures, providing new routes for rational design and engineering of functional micro-/nanomaterials. In one recent study, we firstly reported a facile strategy to synthesize ellipsoidal mesoporous silica nanomaterials (EMSNs) with well-ordered parallel channels along the short axis using cetyltrimethylammonium bromide (CTAB) and tyrosine as structure directing agents and tetraethyl orthosilicate (TEOS) as a silica precursor in dilute ammonia solution. Miniaturized microfluidic device with spiral-shaped channels was then chosen as a self-template directing tool to produce the hollow counterparts of EMSNs using phosphate buffered saline (PBS) as the etching agent and bovine serum albumin (BSA) protein


as the surface protective coating agent at room temperature. Such microfluidic reactor was demonstrated to be a general platform for producing hollow nanostructures and exhibited more rapid and efficient capabilities than conventional batch reactor. The shape evolution toward hollow nanostructure was primarily determined by the flow rates (i.e., etching time). Both EMSNs and HEMSNs exhibited superior performance in nanomedicine, such as high drug loading capacity, controllable drug release, and enhanced cancer cell inhibition activity (Figure 1).

These results not only provide new routes to synthesize anisotropic nanomaterials but also help for systematically understanding of nano-bio interactions. Using the similar strategy, we also realized the ultrafast synthesis of multifunctional submicrometer-scale hollow mesoporous silica spheres in microfluidic spiral channels. In another study, on the basis of spiral-shaped microfluidic reactor, we firstly developed a facile and general flow synthesis strategy to prepare mesoporous silica nanofibers (MSNFs). The aspect ratios and diameters of MSNFs can be easily tuned by changing the flow rates or the concentrations of reactants. Different kinds of functional molecules/nanoparticles, including fluorescent dyes, magnetic nanoparticles, therapeutic drugs, and silver nanoparticles, can be simultaneously assembled into MSNFs to make them promising functional materials in bioimaging, theranostics, and catalysis fields (Figure 2)