The Fabrication and Applications of Protein Patterns Produced Via Particle Lithography

A novel particle lithography technique with the ability to pattern protein in hexagonal dot arrays was developed. The patterning method consists of a simple three-step procedure: (1) formation of a close-packed polystyrene microsphere monolayer, (2) grafting of a protein-resistant layer of poly(ethylene glycol) (PEG), and (3)selective adsorption of protein into the resulting PEG holes. The diameter and center-to-center spacing of the patterned features was varied simultaneously by changing the diameter of the spheres used in the lithographic mask or independently using a simple heating modification. A combination of the original and modified procedures was used to produce patterns of protein dots with diameters of 450 nm - 9 ìm and center-to-center spacings of 2 - 10 ìm. To demonstrate the applicability of the particle lithography technique, a fluorescent-based immunoassay was created using quantum dot bioconjugates (QDBCs). The millions of protein dot features per patterned substrate served as redundant sampling points that produced a subpicomolar detection limit. Finally, the QDBC patterns were also used to investigate the differences between neutrophil spreading on patterned and homogenously coated anti-PSGL-1 (PL1) surfaces

Superhydrophobic Surface by Replication of Laser Micromachined Pattern in Epoxy/Alumina Nanoparticle Composite

Superhydrophobic surfaces were obtained by superposition of microstructure—defined by replication of laser micromachined masters, with nanostructure—created by durable epoxy/γ-Al₂O₃ nanoparticle composite, used for replication. Hierarchical surface topography thus obtained consisted of hexagonally spaced microcavities and nanoparticle agglomerates, exposed on the replica surface by radio frequency (RF) air plasma etching. Surface topography was further enhanced by rims around the microcavity edges, resulting from nanosecond laser micromachining defects in aluminum masters. Subsequent wet chemical hydrophobization with 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (PFTDTES) provided superhydrophobic behavior in replicas with a microcavity spacing of 30 μm, as indicated by a water contact angle of 160° and a sliding angle of 8°. The preparation method is relatively simple, inexpensive, and potentially scalable.This work was supported by the National Science Centre of Poland through projects nos. 2011/03/N/ST8/05879 and UMO-2012/05/B/ST8/02876. The authors are grateful to Professor Weimin Liu and Professor Feng Zhou of the Lanzhou Institute of Chemical Physics, Chinese Academy of Science, for making the laser micromachining, JEOL SEM, and Drop Shape Analysis equipment available

Synthesis of polymer nanostructures via the use of surfactant surface aggregates as templates.

The subject of this work is the synthesis of polymer nanostructures via the use of surfactant surface aggregates as templates, also termed Template Assisted Admicellar Polymerization (TAAP). The first chapter reviews some of the most current nanopatterning techniques (including both top-down and bottom-up approaches), with particular emphasis on the fabrication of organic and inorganic patterned nanostructures via particle lithography. In chapter 2, highly ordered hexagonal arrays of latex spheres were prepared on highly ordered pyrolytic graphite (HOPG) from a variation of the Langmuir Blodgett technique, using an anionic surfactant (SDS), and a low molecular weight (ca. 10000) polyacrylamide as spreading agents. When a nonionic polyethoxylated (EO = 9) surfactant was used as the spreading agent, no ordered arrays were observed. Based on the correlation found between the surface tension in the presence of the latex particles and the critical concentration at which hexagonal arrangements of latex spheres occurs; a model was proposed to explain the role of the spreading agent in forming stable monolayers at the air/liquid interface, which in turn are necessary for the formation of well-ordered monolayers on a solid substrate from the LB technique. According to this model, solid-like regions of small numbers of latex spheres form at the liquid-air interface, which are then transferred to the substrate. These ordered regions then act as nuclei for the formation of 2D arrays of latex spheres on the surface upon water evaporation. The role of other factors such as relative humidity, substrate and solvent choice, and pulling vs. compression speed were also found to affect the quality of the monolayers formed. Finally, a simple, easy to automate, yet effective surface tension method was proposed to predict the optimal conditions for the formation of ordered monolayers using a variation of the LB deposition method from any monodisperse set of spheres.In chapter 3, a novel method for the formation of nanometer-scale polymer structures on solid surfaces via template assisted admicellar polymerization (TAAP) is described. Admicellar polymerization uses a surfactant layer adsorbed on a surface to localize monomer to the surface prior to polymerization of the monomer. TAAP refers to nanostructures that form by restricting adsorption to the uncovered sites of an already-templated surface. In this case, the interstitial sites between adsorbed latex spheres were used as the template. Unlike most other process that form polymer nanostructures, polymer dimensions can be significantly smaller than the interstitial size because of sphere-surfactant-monomer interactions. As a proof of concept, nanostructures formed via TAAP were compared to structures prepared by others via adsorption of three different proteins (Bovine serum albumin, fibrinogen, and anti-mouse IgG) in the interstitial sites of colloidal monolayers. The size and shape of the nanostructures formed (honeycomb vs. pillars) was dependent upon the size of the spheres utilized and the method of polymer deposition (i.e. admicellar polymerization vs. polymer adsorption). Thinner honeycomb walls, and larger separation distances between the template and the nanostructures were consistently found for TAAP.In chapter 4, an in-depth study of the factors affecting TAAP is presented for three different monomers: aniline, pyrrole and methyl methacrylate; and three different surfaces: highly ordered pyrolytic graphite (HOPG), gold, and SiO2. Among the parameters discussed are the effect of monomer and surfactant concentration, surfactant chain length, polymerization time and temperature, solution ionic strength, substrate choice and surface treatment. Control over these parameters allowed the synthesis of polymer nanopillars, nanorings, honeycombs, and "honeytubes." Experimental results showed that the nanostructures' morphology can be effectively modified by changing the length of the hydrophobic chain of the surfactant. Nanostructures with fewer defects were found for surfactants with the longest hydrophobic tails (i.e. 12 carbon atoms). The hydrophobic nature of the monomer also seemed to affect the morphology of the nanostructure; poly(methyl methacrylate) (PMMA) honeycombs showed thicker walls compared to polyaniline (PANI) and polypyrrole (Ppy). In general, HOPG seems to be a better choice of substrate for TAAP compared to gold-coated glass and SiO2 wafers. Preliminary results on the formation of layered polymer nanostructures via multiple TAAP sequences were also presented

Hierarchical Assemblies of Soft Matters From Polymers and Liquid Crystals on Structured Surfaces

Hierarchical, multifunctional materials hold important keys to numerous advanced technologies, including electronics, optics, and medicine. This thesis encompasses generation of hierarchical structures with novel morphologies and functions through self-assembly directed by lithographically fabricated templates. Here, two soft materials, amphiphilic random copolymers of photopolymerized acryloyl chloride (ranPAC) and smectic-A liquid crystal (SmA-LC) molecule, 4\u27(5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heptadecaflu-orododecyloxy)-biphenyl-4-carboxylic acid ethyl ester, are synthesized as model systems to investigate the governing principles at the topographic surface/interface. The ranPAC can self-organize into nanomicelles with high regularity and stability, typically not possible in random copolymer systems. The morphology can be controlled by the photopolymerization conditions and solvent; the crosslinked shell makes the micelles robust against drying and storage. Using SU-8 micropillar arrays with spatially controlled surface chemistry as templates, we construct hierarchical microporous structures with tunable pore size and symmetry (e.g. square array), and uncover a new evaporative assembly method. By functionalizing the ranPAC nanovesicles with cationic poly(ethyleneimines), we encapsulate the anticancer drug, doxorubicin hydrochloride, and mRNA at a high payload, which are delivered to HEK 293T cells in vitro at a low cytotoxicity level. SmA-LC are characterized by arrangement of molecules into thin layers with the long molecular axis parallel to the layer normal, forming a close-packed hexagonal array of topological defects known as focal conic domains (FCDs) in a thin film. Using a series of SU-8 micropillar arrays with different size, shape, height, and symmetry as topological templates, we investigate the epitaxial and hierarchical assemblies of FCDs; whether the system favors confinement or pillar edge-pinning depends on balance of the elastic energy of LCs and the surface energy imposed by the template. The conservation of toric FCD (TFCD) textures over large LC thickness manifests a remarkably unique outcome of the epitaxial growth of TFCDs. On shorter pillars, however, the system favors the pinning of FCD centers near pillar edges while avoiding the opposing effect of confinement, leading to the break of the underlying symmetry of the pillar lattice, exhibiting tunable eccentricity, and a nontrivial yet organized array of defects balancing the elastic energy of LCs and the surface energy imposed by the template

Fabrication of Organosilane Nanostructures as Selective Sites for Surface Chemical Reactions

Naturally self-assembled mesospheres provide a practical route for controlling the arrangement of materials on surfaces at the nanoscale. Periodic arrays of well-defined nanostructures can be produced with different nanomaterials and interpattern spacings. Results presented in this dissertation demonstrate particle lithography methods developed for fabricating arrays of organosilane nanostructures. Surfaces were designed for the selective deposition of polymers and nanoparticles to produce multicomponent nanopatterns. The approaches for surface patterning provide new directions for studying surface chemistry at the molecular-level, and have practical application for emerging photovoltaic thin film technologies. Atomic force microscopy (AFM) provides unique capabilities for molecular visualization and ultrasensitive measurements of surface properties with nanoscale resolution. Organosilane nanopatterns bearing different functionalities and chain lengths were characterized using AFM to gain insight on molecular organization and surface-assembly processes. Indirect magnetic modulation (IMM) is a new instrument configuration for force modulation AFM that was developed for investigating mechanical properties of materials. The principle of IMM is based on indirect oscillation of soft nonmagnetic cantilevers through the tip holder assembly, which contains magnetic materials. Imaging can be performed in either ambient or liquid environments. The driving frequency for tip vibration can be selected to enhance contrast in amplitude and phase images, which provides information on the elastic response of thin-film materials. Images acquired with IMM furnish nanoscale resolution views of the morphology and elastic response of organosilane nanostructures. The dampening effect of liquid imaging media on cantilever oscillation during IMM was investigated using a liquid sample cell. Organic photovoltaic (OPV) devices are promising alternatives to traditional silicon based solar cells. A major challenge for OPVs is the requirement for higher efficiencies, or better device performance. The nanoscale morphology and molecular organization of the donor/acceptor materials in the organic layer affects the conductivity of OPV devices. To improve efficiency, new fabrication methods must be developed that are capable of controlling the molecular structure of the donor/acceptor materials. Using particle lithography combined with contact printing, billions of periodic and uniform pillar nanostructures of polythiophene can be fabricated on the surface. The dimensions and spacing can be selectively tuned by using different size latex masks

Nanophotonics of 2-Dimensional Materials

2-Dimensional materials are of great interest because of novel and intriguing properties that emerge at the monolayer limit in comparison to bulk materials. To that end, this thesis is split into the study of two different 2-dimensional materials in the realm of nanophotonics. First, graphene is utilized for both passivating the surface of metallic nanoparticles from oxidation and as a platform for functionalization and integration into specific molecule sensing. The nanoparticles act as plasmonic nanoantennas, enhancing the electric field near the surface of the antenna. It is shown that graphene-encapsulated silver nanoantennas are oxidation resistant and optically stable over a 30 day period. The performance of the graphene-passivated silver nanoantennas outpaces that of the traditional material, gold, by ~60% in sensing bulk index changes in the range of n = 1.40 1.45. Graphene encapsulation can be extended to other plasmonic metals such as aluminum and copper, as well as fully integrate graphene-passivated Ag nanoantennas into biomolecular sensing devices. The second topic of this thesis is to study and enhance the luminescence of molybdenum disulfide (MoS2), a 2-dimensional semiconductor. Atomic layer deposition of SiO2 was used to encapsulate and the effectively etch a layer of bilayer MoS2 through reactive processes, which result in a chemically-doped MoS2 monolayer with enhanced luminescence properties. This new enhanced layer is two orders of magnitude more luminescent than the original material and one order of magnitude over that of an exfoliated monolayer. By coupling the enhanced MoS2 to an optical microdisk cavity, highly narrow emission can be produced from the original, broad luminescence. These sharp peaks can be utilized in biomolecule sensing through functionalization of the MoS2 layer. The effects of high-intensity optical pumping of the MoS2 in these microdisk cavities are also studied. Heat generation from non-radiative recombination causes thermally enabled oxidation of the optical material. This effect is shown to be not limited to MoS2, but affects WSe2 as well. This effect is shown to be minimized through the use of pulsed excitation, and the luminescence from high Q-factor microdisks was investigated using high-fluence femtosecond optical pulses