Micro/nanopatterning approaches for molecular manipulation
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Nanotechnology has a steadily increasing impact on worldwide research and business activities. This work explores advanced micro/nano patterning approaches for molecular manipulation. The objectives are to (1) build a proper bridge from a few microns to the 100-10 nm range and below as well as to (2) combine “top-down” precise design with the “bottom-up” size scale to create designed surfaces, areas and volumes that can interact with molecules in a designed way. Three studies were designed and studied accordingly. The first investigation demonstrates that “top-down” Inclined Nanoimprinting Lithography (INIL) is able to produce three-dimensional (3-D) nanopatterns of varying heights in a single step. INIL reduces pattern's feature size from microns to nanometers. The degree of resulting nanopattern's asymmetry can be controlled by the magnitude of the inclination angle. Various 3-D nanostructures are successfully demonstrated including nanolines, nanocircles and nanosquares. The underlying INIL mechanism is investigated, which is primarily due to the induced shear force when the inclination angle is not zero. This leads to the anisotropic dewetting of polymer fluid and consequently asymmetric 3D nanopatterns of varying heights. INIL removes the need of preparation of expensive 3D nanotemplates or multiple template-to-substrate alignments. In addition, such 3-D structures are successfully transferred to silicon, silicone rubber and metal gold. INIL enables 3D nano-scale devices including angle-resolved photonic and plasmonic crystals. The second investigation demonstrates the success of “bottom-up” molecular imprinting of X-ray contrast agent iodixanol in polymer matrix. The synthetic tailor-made molecularly imprinted polymers (MIPs) are poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) which possess specific binding sites induced by the template molecules of X-ray contrast agent iodixanol. It leads the feature size reduction from macromolecules to molecular scale. The properly imprinted binding sites also leads MIPs to have improved absorption capacity and efficiency for X-ray contrast agent iodixanol relative to non-imprinted polymers. The best binding capacity achieved from the optimized MIPs was 284 mg/g in aqueous solution, 8.8 times higher than that of the non-imprinted polymers. The best binding capacity obtained in sheep plasma was 232 mg/g, 4.5 times higher than the non-imprinted polymers. The factors that may affect the binding performance of MIPs in aqueous media are studied. The optimized MIPs are encouraging for biomedical implementations including dialysis and nanosensors. The third investigation of nanolithography-based molecular manipulation (NMM) explores a hybrid approach by combining “top-down” electron-beam lithography (EBL) with “bottom-up” surface initiated polymerization (SIP). It reduces the nanopattern's feature size to sub-10 nm and simultaneously tunes its surface chemistry through functional polymer brushes. The process has reduced process complexity and cost. The demonstrated prototype molecular manipulation templates have 3D surface nanostructures with sub-10 nm feature size and anisotropic surface functionalities. They mimic biocatalyst enzymes to “bottom-up” assemble nanoparticle targets at specific locations producing 3D nanostructures in a designated way. Various 3D synthetic nanostructures have been demonstrated including polystyrene “nanomushrooms” “nanospikes”, “nanofibers” and polystyrene-iron oxide “nanoflowers”. Potential applications of these synthetic 3D nanostructures can be improved therapeutic agents. This hybrid strategy realizes the integration of “top-down” design with “bottom-up” molecular scale to create designed nanopatterned surfaces that can interact with molecules in a designated way.