One-dimensional nanostructures have offered unique advantages in many fields. Protein based nanotubes, in particular, are desirable for biomedical applications due to their ease of functionlization and intrinsic biocompatibility. Template-assisted methods are widely used to fabricate cylindrical nanostructures like carbon nanotubes, metal nanowires, polymer nanorods, etc. In the fabrication of protein nanostructures, the layer by layer (LbL) technique has long been applied to deposit protein multilayers on planar and spherical substrates. The success in each area led to the conclusion that the combination of these two techniques will potentially bring us the capability of fabricating protein nanotubes in a more controllable fashion. In this work, protein nanotubes have been successfully deposited inside nanoscopic pores by sequential filtration of bovine serum albumin (BSA) solution at pH 3.8 and pH 7.0 through the channels in the anodic aluminum oxide (AAO) template. The morphologies of the obtained nanostructures have been examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Also, a simple analysis from UV/Vis spectroscopy has shown that the solutions used in our experiment will not significantly damage the bioactivity of BSA. Our future work will focus on strengthening the mechanical stability of the protein nanotubes and controlling their morphology more precisely.

Conductive thin films of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT-PSS) were created via layer-by-layer assembly. The PEDOT-PSS was used in an aqueous solution as an anionic polyelectrolyte, with both linear and branched polyethylenimine (PEI) and poly(allylamine hydrochloride) (PAH) in the positive aqueous solution. The electrical conductivity was varied by altering pH, concentration, polyelectrolyte, and doping the PEDOT with dimethylsulfoxide (DMSO). The most conductive 12BL samples were doped with 1wt% DMSO and have a sheet resistance of approximately 8kΩ/□. Despite exhibiting good initial conductivity, these PEDOT based thin films degrade under ultraviolet (UV) exposure. UV absorbing nanoparticles were added into the cationic solution in an effort to reduce UV sensitivity. The final bilayers of the films contained either colloidal titanium dioxide (TiO2) or carbon black (CB) and the films were exposed to a 365nm UV-light with an intensity of 2.16mW/cm2 for 9 days. The UV light at this intensity correlates to approximately four years of sunlight. The initial sheet resistances for all samples were similar, but the UV-degradation was reduced by a factor of 5 by utilizing TiO2 and CB in the final bilayers. In addition to being the most conductive after UV exposure, the TiO2 containing film was also 27% more optically transparent than the pure PEDOT films. These additional UV-absorbing nanoparticles extend the operational life of the PEDOT films and, in the case of TiO2, do so without any reduced transparency.

Polyelectrolyte microcapsules containing stimuli-responsive polymers have potential applications in the fields of sensors or actuators, stimulable microcontainers and controlled drug delivery. Such capsules were prepared, with the focus on pH-sensitivity and carbohydrate-sensing. First, pH-responsive polyelectrolyte capsules were produced by means of electrostatic layer-by-layer assembly of oppositely charged weak polyelectrolytes onto colloidal templates that were subsequently removed. The capsules were composed of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) or poly(4-vinylpyridine) (P4VP) and PMA and varied considerably in their hydrophobicity and the influence of secondary interactions. These polymers were assembled onto CaCO3 and SiO2 particles with diameters of ~ 5 µm, and a new method for the removal of the silica template under mild conditions was proposed. The pH-dependent stability of PAH/PMA and P4VP/PMA capsules was studied by confocal laser scanning microscopy (CLSM). They were stable over a wide pH-range and exhibited a pronounced swelling at the edges of stability, which was attributed to uncompensated positive or negative charges within the multilayers. The swollen state could be stabilized when the electrostatic repulsion was counteracted by hydrogen-bonding, hydrophobic interactions or polymeric entanglement. This stabilization made it possible to reversibly swell and shrink the capsules by tuning the pH of the solution. The pH-dependent ionization degree of PMA was used to modulate the binding of calcium ions. In addition to the pH-sensitivity, the stability and the swelling degree of these capsules at a given pH could be modified, when the ionic strength of the medium was altered. The reversible swelling was accompanied by reversible permeability changes for low and high molecular weight substances. The permeability for glucose was evaluated by studying the time-dependence of the buckling of the capsule walls in glucose solutions and the reversible permeability modulation was used for the encapsulation of polymeric material. A theoretical model was proposed to explain the pH-dependent size variations that took into account an osmotic expanding force and an elastic restoring force to evaluate the pH-dependent size changes of weak polyelectrolyte capsules. Second, sugar-sensitive multilayers were assembled using the reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties that were grafted onto poly(acrylic acid) (PAA). The resulting multilayer films were sensitive to several carbohydrates, showing the highest sensitivity to fructose. The response to carbohydrates resulted from the competitive binding of small molecular weight sugars and mannan to the boronic acid groups within the film, and was observed as a fast dissolution of the multilayers, when they were brought into contact with the sugar-containing solution above a critical concentration. It was also possible to prepare carbohydrate-sensitive multilayer capsules, and their sugar-dependent stability was investigated by following the release of encapsulated rhodamine-labeled bovine serum albumin (TRITC-BSA). / Die Entwicklung von stimulisensitiven Systemen hat in den vergangenen Jahren großes Interesse hervorgerufen. Diese Systeme verändern ihre Eigenschaften in Abhängigkeit von äußeren Einflüssen und haben potenzielle Anwendungsgebiete im Bereich von Sensoren und der kontrollierten Wirkstofffreisetzung. Beispiele für äußere Einflüsse sind die Temperatur, die Salzkonzentration der Lösung, der pH-Wert oder die Gegenwart bestimmter chemischer Substanzen. Polyelektrolyt-Multischicht-Hohlkugeln stellen viel versprechende stimulisensitive Systeme dar, da sie aus dünnen Membranen mit veränderbaren Eigenschaften aufgebaut sind, und eingekapselte Substanzen definiert freigesetzt werden können. Im Rahmen dieser Arbeit wurden zum einen Polyelektrolytkapseln untersucht, deren Stabilität, Größe und Durchlässigkeit abhängig ist vom pH-Wert und der Salzkonzentration der Lösung. Zum anderen wurden Hohlkugeln entwickelt, deren Stabilität durch die Gegenwart verschiedener Zucker in der umgebenden Lösung beeinflusst wurde. Hierbei war es möglich, eine eingekapselte Substanz in Abhängigkeit der Zuckerkonzentration der Lösung freizusetzen. pH-sensitive Polyelektrolyt-Hohlkugeln wurden mit Hilfe der elektrostatischen Layer-by-Layer Methode aufgebaut. Hierbei wurden abwechselnd schwache Polysäuren und Polybasen auf kolloidalen Partikeln adsorbiert und in einem weiteren Schritt wurde das Templat entfernt. Als Polyelektrolyte fanden Poly(allylaminhydrochlorid) (PAH) und Poly(methacrylsäure) (PMA) bzw. Poly(4-vinylpyridin) (P4VP) und PMA Verwendung. Diese zwei Systeme unterscheiden sich in ihren hydrophoben Eigenschaften und dem Einfluss von Sekundärwechselwirkungen. Die Polymere wurden auf CaCO3 und SiO2 Partikeln mit Durchmessern von ~ 5 µm aufgebracht, und eine neue Methode zum Entfernen des Silica-Templats wurde vorgestellt. Die pH-abhängige Stabilität von PAH/PMA und P4VP/PMA Hohlkugeln wurde mit der konfokalen Fluoreszenzmikroskopie untersucht. Beide Systeme waren über einen breiten pH-Bereich stabil und zeigten an der Grenze der Stabilität ein ausgeprägtes Schwellen, das den unkompensierten positiven oder negativen Ladungen der Mulitschichten zugeordnet werden konnte. Gab es innerhalb der Multischichten stabilisierende Wechselwirkungen, z.B. Wasserstoffbrückenbindungen oder hydrophobe Anziehungskräfte, welche der elektrostatischen Destabilisierung entgegenwirkten, so ließ sich der geschwollene Zustand stabilisieren. Diese Stabilisierung ermöglichte das reversible Schwellen der Hohlkugeln durch Veränderung des pH-Wertes der Lösung. Der pH-abhängige Ionisationsgrad von PMA wurde zur Bindung von Calcium-Ionen verwendet. Die Stabilität und das Schwellen der Hohlkugeln konnten durch Variation der Ionenstärke der Lösung modifiziert werden. Das reversible Schwellen wurde von reversiblen Permeabilitätsänderungen für nieder- und hochmolekulare Substanzen begleitet. Die Permeabilität für Glucose wurde mit Hilfe der Zeitabhängigkeit der Verformung der Kapselmembranen in Glucoselösungen untersucht, und die reversible Veränderung der Permeabilität wurde zur Einkapselung von Polymeren verwendet. Die pH-abhängigen Größenänderungen ließen sich mit einem theoretischen Modell beschreiben, das von einem Kräftegleichgewicht zwischen einer osmotischen expansiven Kraft und einer elastischen kontraktiven Kraft ausging. Als zweites stimulisensitives System wurden zuckersensitive Multischichten untersucht. Diese wurden über reversible kovalente Esterbindungen stabilisiert. Als Polymere für den Schichtaufbau fanden das Polysaccharid Mannan und Polyacrylsäure, die mit Aminophenylboronsäure modifiziert war, Verwendung. Die daraus entstehenden Multischichten waren sensitiv gegenüber verschiedenen Kohlenhydraten, mit der größten Selektivität für Fructose. Diese Affinitäten ergaben sich aus der kompetitiven Bindung zwischen niedermolekularen Zuckern und Mannan an die Boronsäuregruppen. Oberhalb einer kritischen Zuckerkonzentration kam es zur schnellen Auflösung der Multischichten. Darüber hinaus war es möglich zuckersensitive Polymerkapseln herzustellen, deren zuckerabhängige Stabilität durch die Freisetzung von eingekapseltem Rinderserumalbumin verfolgt wurde.

Aflatoxin is a potent biological toxin produced by fungi Aspergillus flavus and A. parasiticus. Current quantification methods for aflatoxins are mostly established on immunoaffinity columns which are both costly and labor intensive. Inspired by smectites’ high aflatoxin adsorption capacity and affinity, a novel aflatoxin quantification sensor based on smectite-polyacrylamide (PAM) nanocomposite was fabricated. First, a smectite-PAM nanocomposite film was synthesized on flat silicon substrates which assembled smectite particles from the clay suspension. A layer-by-layer assembly process was developed to achieve uniform morphology and thickness of the nanocomposite films. During the aflatoxin quantification process, positive correlations between the fluorescence intensity from the aflatoxin B1 (AFB1) adsorbed smectite-PAM nanocomposite films and the AFB1 concentration in the test solutions were obtained. The smectite-PAM nanocomposite film has shown similar AFB1 adsorption capabilities as the smectite. Second, the smectite-PAM nanocomposite film was optimized in order to achieve the aflatoxin quantification at ppb level (below 20ppb) in corn extraction solutions. The smectite was modified by Ba2+, which had demonstrated to be able to improve its aflatoxin adsorption capacity. PAM aqueous solutions with the mass concentration ranging from 0.8% to 0.001% were tested. The results showed that the nanocomposite synthesized from 0.005% concentration of PAM solution generated the best properties. After the optimization, the smectite-PAM nanocomposite films achieved the detection of aflatoxin B1, B2, G1 and G2 (AFB2, AFG1 and AFG2) in 10 ppb corn extraction solution. Aflatoxin quantifications in AFB1 and AFB2 mixture solution, AFB1 and AFB2 mixture solution and AFB1 and AFG1 mixture solution were conducted, and the recoveries of last test ranged from 90.52% to 110.11% at low aflatoxin concentration (below 20 ppb). Third, in order to shorten the quantification duration and simplify the detection process, a novel aflatoxin detection array based on smectite-PAM nanocomposite and an improved fluorometric quantification method were developed. Through a microfluidic chip, the reaction time was reduced to 10~20min. Two concentration levels (20~80ppb/5~15ppb) of aflatoxin B1 spiked corn extraction solutions were tested. In the fluorometric quantification step, a common lab-use 365 nm ultraviolet lamp replaced the spectrofluorometer which simplified and accelerated the process.

Numerous studies have focused on enhancing the flame retardant behavior of cotton and polyurethane foam. Some of the most commonly used treatments (e.g., brominated compounds) have raised concerns with regard to toxicity and environmental persistence. These concerns have led to significant research into the use of alternative approaches, including polymer nanocomposites prepared from more environmentally benign nanoparticles. These particles migrate to the surface from the bulk during fire exposure to form a barrier on the surface that protects the underlying polymer. This theory of fire suppression in bulk nanocomposites inspired the use of layer-by-layer (LbL) assembly to create nanocoatings in an effort to produce more effective and environmentally-benign flame retardant treatments. Negatively charged silica nanoparticles of two different sizes were paired with either positively charged silica or cationic polyethylenimine (PEI) to create thin film assemblies. When applying these films to cotton fabric, all coated fabrics retained their weave structure after being exposed to a vertical flame test, while uncoated cotton was completely destroyed. Micro combustion calorimetry confirmed that coated fabrics exhibited a reduced peak heat release rate, by as much as 20% relative to the uncoated control. Even so, this treatment would not pass the standard UL94 vertical flame test, necessitating a more effective treatment. Positively- charged chitosan (CH) was paired with montmorillonite (MMT) clay to create a renewable flame retardant nanocoating for polyurethane foam. This coating system completely stops the melting of a flexible polyurethane foam when exposed to direct flame from a butane torch, with just 10 bilayers (~ 30 nm thick). The same coated foam exhibited a reduced peak heat release rate, by as much as 52%, relative to the uncoated control. This same nanobrick wall coating is able to impart gas barrier to permeate plastic film. Multilayered thin films were assembled with "green" food contact approved materials (i.e., chitosan, polyacrylic acid (PAA) and montmorillonite clay). Only ten CH-PAA-CH-MMT quadlayers (~90 nm thick) cause polylactic acid (PLA) film to behave like PET in terms of oxygen barrier. A thirty bilayer CH-MMT assembly (~100 nm thick) on PLA exhibits an oxygen transmission rate (OTR) below the detection limit of commercial instrumentation (<= 0.005 cm^3/(m^2*day*atm)). This is the same recipe used to impart flame retardant behavior to foam, but it did not provide effective FR to cotton fabric, so a very different recipe was used. Thin films of fully renewable electrolytes, chitosan and phytic acid (PA), were deposited on cotton fabric in an effort to reduce flammability through an intumescent effect. Altering the pH of aqueous deposition solutions modifies the composition of the final nanocoating. Fabrics coated with highest PA content multilayers completely extinguished the flame and reduced peak heat release (pkHRR) and total heat release of 60% and 76%, respectively. This superior performance is believed to be due to high phosphorus content that enhances the intumescent behavior of these nanocoatings.

Conductive thin films of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT-PSS) were created via layer-by-layer assembly. The PEDOT-PSS was used in an aqueous solution as an anionic polyelectrolyte, with both linear and branched polyethylenimine (PEI) and poly(allylamine hydrochloride) (PAH) in the positive aqueous solution. The electrical conductivity was varied by altering pH, concentration, polyelectrolyte, and doping the PEDOT with dimethylsulfoxide (DMSO). The most conductive 12BL samples were doped with 1wt% DMSO and have a sheet resistance of approximately 8kΩ/□. Despite exhibiting good initial conductivity, these PEDOT based thin films degrade under ultraviolet (UV) exposure. UV absorbing nanoparticles were added into the cationic solution in an effort to reduce UV sensitivity. The final bilayers of the films contained either colloidal titanium dioxide (TiO2) or carbon black (CB) and the films were exposed to a 365nm UV-light with an intensity of 2.16mW/cm2 for 9 days. The UV light at this intensity correlates to approximately four years of sunlight. The initial sheet resistances for all samples were similar, but the UV-degradation was reduced by a factor of 5 by utilizing TiO2 and CB in the final bilayers. In addition to being the most conductive after UV exposure, the TiO2 containing film was also 27% more optically transparent than the pure PEDOT films. These additional UV-absorbing nanoparticles extend the operational life of the PEDOT films and, in the case of TiO2, do so without any reduced transparency.

Layer-by-layer (LbL) assembly based on ionic interactions has proven to be a versatile route for surface modification and construction of ultrathin nanocomposites. Covalent LbL assembly based on facile ‘click’ covalent bond formation is an effective alternative, especially for the applications where a more robust ultrathin films or nanocomposites is desired. The subject of this dissertation focuses on the design of three different covalent LbL assemblies and their applications on conductive thin films, superhydrophobic surfaces, and solute responsive surfaces, respectively. Surface modification of PE substrates using covalent LbL assembly with PEI and Gantrez is a successful route to prepare a surface graft. The procedure is relative easy, fast and reproducible. Grafting multiple layers of PEI/Gantrez to the PE powder surface provided excellent coverage and promoted stable LbL film growth and excellent adhesion. This carbon black (CB) coated powder was compression molded into films, and their conductivity was measured, which revealed a percolation threshold below 0.01 wt % CB for the PEI-grafted system. Electrical conductivity of 0.2 S/cm was achieved with only 6 wt % CB, which is exceptional for a CB-filled PE film. Direct amination of MWNTs with PEI is a convenient and simple method leading to highly functionalized product that contains 6-8 % by weight PEI. Superhydrophobic PE films can be formed either from ionic LbL self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent LbL self-assembly of MWNTNH- PEIs and Gantrez when the final graft is acrylated with octadecanoic acid. While the ionically assembled nanocomposite graft is labile under acid, the covalently assembled graft is more chemically robust. Responsive surfaces with significant, reversible, reproducible wettability changes can be prepared by covalent LbL grafting using PNIPAM-c-PNASI and aminated silica nanoparticles. A 65º ΔΘ value was observed with water vs. 1.4 M Na2SO4. The prepared film shows a high surface roughness of ~300 nm, which contributes to the large solute responsive ΔΘ values. The surfaces are reconfigurable in different solute conditions and that the changes in water contact angle are likely due to combination of change in surface roughness along with swell and intercalation of the solute ions into the PNIPAM surface.

Layer-by-layer (LbL) assembly has proven to be a powerful technique for assembling thin films with a variety of properties including electrochromic, molecular sensing, oxygen barrier, and antimicrobial. LbL involves the deposition of alternating cationic and anionic ingredients from solution, utilizing the electrostatic charges to develop multilayer films. The present work incorporates cationic antimicrobial agents into the positively-charged layers of LbL assemblies. When these thin films are exposed to a humid environment, the antimicrobial molecules readily diffuse out and prevent bacterial growth. The influence of exposure time, testing temperature, secondary ingredients and number of bilayers on antimicrobial efficacy is evaluated here. Additionally, film growth and microstructure are analyzed to better understand the behavior of these films. The antimicrobial used here is a positively-charged quaternary ammonium molecule (e.g. cetyltrimethylammonium bromide [CTAB]) that allow assemblies to be made with or without an additional polycation like polydiallyldimethylamine. While films without this additional polymer are effective, they do not have the longevity or uniformity of films prepared with its addition. All of the recipes studied show linear growth as a function of the number of bilayers deposited and this growth is relatively thick (i.e. > 100 nm per bilayer). In general, 10-bilayer films prepared with CTAB and poly(acrylic acid) are able to achieve a 2.3 mm zone of inhibition against S. aureus bacteria and 1.3 mm against E. coli when test are conducted at body temperature (i.e. 37oC). Fewer bilayers reduces efficacy, but lower test temperatures improve zones of inhibition. As long as they are stored in a dry atmosphere, antimicrobial efficacy was found to persist even when films were used four weeks after being prepared. The best films remain effective (i.e. antimicrobially active) for 4-6 days of constant exposure to bacteria-swabbed plates. This technology holds promise for use in transparent wound bandages and temporary surface sterilization.

An amperometric glucose biosensor was fabricated using electospun polyaniline fibers. Polyaniline was reacted with camphorsulfonic acid to produce a salt, which was then dissolved in chloroform containing polystyrene. Using this solution, fibers were formed and collected by electrospinning. Glucose oxidase was immobilized onto these fibers using an electrostatic layer-by-layer adsorption technique. In this method, poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and evidence of layer-by-layer adsorption was obtained using a quartz crystal microbalance technique. A biosensor was fabricated from these fibers as a working electrode, and used to measure the glucose concentration accurately.

Microgels are solvent swollen, cross-linked polymer macromolecules of micro or nanoscale dimensions. In this work, microgels are used as versatile building blocks in layer-by-layer assemblies to form thin coatings. While conceptually simple materials, these microgel-based films actually possess extremely complex behavior as evidenced by two particular areas. First, microgel films have self-healing properties, allowing them to rapidly recover from damage in the presence of solvent. The healing step requires rearrangement of film components, demonstrating the dynamic and mobile nature of the films. Second, fibroblasts display complex behavior on microgel films arising from the properties of the coating. A chemical crosslinking treatment of the film affects the film network structure in a concentration-dependent manner. These network changes result in altered mechanical properties that are the primary controlling factor in determining cell behavior at the interface. These data suggest that fibroblasts are not solely controlled by the film elasticity, but rather by the viscoelasticity, and there is a viscoelastic range that results in maximal cell spreading.