Inverse opals (IOs) are porous materials with enhanced mechanical, chemical, thermal, and photonic properties used to improve the performance of many technologies, such as battery electrodes, photonic devices, heat exchangers, and biomedical tissue scaffolds\[1, 2\]. The size of these materials, however, is limited to \~1 cm^2^ areas, which restricts their useful applications. Here, we report the fabrication of up to 25 cm^2^ free-standing nickel IOs enabled by new insights into the fracture of drying colloidal solutions. We also develop a method to control the internal pore size (from 100 to 650 nm), which we demonstrate increases the capture efficiency of immunomagnetic exosome separation by up to 50X compared to commercial membranes.

The fabrication of free-standing nickel IOs involves drop-casting 2 um particle suspensions on functionalized ITO substrates, dip-coating the template with a resin-ethanol mixture to form resin capillary bridges between particles, electrodepositing nickel through the particle templates, and removal of templates. The casting method for assembling particle templates significantly decreases the time required for particle assembly compared to current vertical self-assembly methods and is easy to scale up. By controlling the concentration of resin, the diameter of capillary bridges can be precisely adjusted from 100 up to 650 nm, which determines the internal pore size of nickel IOs and reduces the flow resistance. As opposed to other methods of pore size control, such as template sintering and electropolishing that sacrifice the IO's strength down to few tens of megapascal, our experiments and simulation show that the capillary bridge method can maintain the strength of nickel IOs to be 100 MPa, which maintains high liquid flow-through rates and allows the membrane survive post-fabrication handling. To demonstrate the proposed fabrication method, we fabricated free-standing nickel IO with 650 nm internal pore size and 5x5 cm^2^ in area. 

We apply these nickel IOs to the immunomagnetic separation of exosomes by conformally-coating a layer of nickel-iron and gold on top of the nickel IOs using pulse electrodeposition. These functional layers increase the magnetic performance and prevent nickel leaching, which is toxic to biological samples. The resulting membranes feature millions of nanoscale pores which are each capable of magnetically sorting exosomes via immunomagnetic labeling with surface-marker-specific magnetic nanoparticles. Finite-element analysis simulations show that strong magnetophoretic traps emerge at the pore boundaries in this structure between higher-permeability nickel-iron permalloy and the lower-permeability sample fluid flowing through the IO membrane. Compared to commercial track-etch membranes, conformally-coated IO nanostructures offer \>1000x pore density, thus enabling significantly higher flow rates. Preliminary experimental data shows that our membranes can isolate iron nanoparticles in solution with 100x more enrichment versus input, and 49x capture efficacy and 5x faster versus commercial membranes.

 

1.         Armstrong, E. and C. O'Dwyer, *Artificial opal photonic crystals and inverse opal structures - fundamentals and applications from optics to energy storage.* Journal of Materials Chemistry C, 2015. 3(24): p. 619-6143.

2.         Zhang, Y.S., C. Zhu, and Y. Xia, *Inverse opal scaffolds and their biomedical applications.* Advanced Materials, 2017. 29(33): p. 1701115.


Tailoring Pore Size and Surface Properties of High-Strength Microporous Nickel Inverse Opals for Fast and Efficient Immunomagnetic Separation of Exosomes

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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