This dissertation presents the development of a new form of biomolecular material system which features interface lipid bilayers capable of hosting a wide variety of natural and engineered proteins. This research builds on the droplet interface bilayer (DIB) platform which first demonstrated that, through self-assembly, lipid-encased water droplets submersed in oil can be physically connected to form a liquid-supported lipid bilayer at the droplet interface. Key advantages of the DIB method over previous bilayer formation techniques include the lack of a supporting substrate which simplifies bilayer formation and the ability to connect many droplets to form `cell-inspired' networks which can provide a collective utility based on the compositions and arrangement of the droplets. The research present herein specifically seeks to overcome three limitations of the original droplet interface bilayer: limited portability due to lack of droplet support, the use of externally supported electrodes to electrically probe the network, and the requirement that in order to form DIB networks, aqueous volumes must be individually dispensed and arranged. The approach presented in this document is to provide increased interactions between the contained liquid phases and a supporting substrate in order to achieve both increased usability through refined methods of packaging and in situ interface formation which eliminates the need to create individual droplets. Physical encapsulation is defined as the the use of a solid substrate to contain both liquid phases such that the aqueous volumes are physically supported on one length scale (10-1000µm) while not inhibiting the self-assembly of phospholipids at the oil/water interface occurring on a much smaller length scale (1-10nm). Physically-encapsulated droplet interface bilayers are achieved by connecting lipid-encased droplets within a substrate that tightly confines the positions of neighboring droplets. A term called the packing factor is introduced to quantify the ratio of the aqueous volumes per the total compartment volume. Physically-encapsulated droplet interface bilayers formed in high packing factor substrate (30%) that also features integrated electrodes demonstrate all of the properties that unencapsulated DIBs exhibit (electrical resistances greater than 1GΩ, failure potentials between |200-300|mV, and the ability to host transmembrane proteins) but these confined assemblies can be moved, shaken, and even completely inverted. Additionally, a structured experiment to quantify the durability of interface bilayers shows that encapsulated and unencapsulated droplet interface bilayers can both survive 3-7g of lateral acceleration prior to bilayer failure, but have different modes of failure. Encapsulated DIBs tend to rupture, while unencapsulated DIBs completely separate. Physical encapsulation is also shown to permit the in situ formation of durable interface bilayers when the substrate is made from a flexible material. The importance of this approach stems from the fact that, by using the substrate to locally partition a single aqueous volume into multiple volumes, there is no need to arrange individual droplets. This method of bilayer formation is termed the regulated attachment method (RAM), since the separation and subsequent reattachment of the aqueous volumes is regulated by the opening and closing of an aperture within the flexible substrate. In this dissertation, a mechanical force is used to directly modulate the aperture dimension for controlling both the initial formation and final size of the interface. With the demonstrated advantages of portability and controlled attachment offered by physical encapsulation, encapsulated lipid bilayers are formed within a completely sealed flexible substrate. A key aspect of this final work is to demonstrate that both the organic and aqueous phases can be stabilized internally, creating a complete material system that features tailorable interface bilayers. / Ph. D.

The formation of lipid bilayer membranes between droplets of ionic liquid is presented as a means of forming functional bimolecular networks for use in sensor applications. Ionic liquids are salts that have a number of useful properties, such as low melting points making them liquid at room temperature and exceedingly low vapor pressure. Ionic liquids have seen recent popularity as environmentally friendly industrial solvent alternatives. Our research demonstrates that it is possible to consistently form lipid bilayers between droplets of ionic liquid solutions. Analysis shows that the ionic liquids have negligible effects on the physical stability and electrical properties of the bilayer. It is also shown that the magnitude of the conductance levels of Alamethicin peptide are altered by some ionic liquids. / Master of Science

No description available.

Cell membranes are integral for many biological processes. In addition to containing and protecting cellular contents and maintaining the chemical integrity of the cell, these interfaces host a variety of ligand-receptor interactions. These ligand-receptor interactions are important for cell signaling and transport and the ability to monitor them is key to understanding these processes. In addition, therapeutics and drug discovery is also aided by membrane-specific study, as the majority of drugs target receptors associated with the cell surface. The cell membrane can be effectively mimicked by the use of supported lipid bilayers, which provide a robust platform exhibiting the lateral fluidity and composition associated with cell membranes. The ability to study both ligand-receptor interactions as well as small molecule-membrane interactions on these model membranes is aided by the fact that these assays can be multiplexed and are amenable to use with low sample volumes with high throughput. Our laboratory has recently developed a strategy for fluorescent microscopy studies of ligand-receptor interactions on supported lipid bilayers without the use of fluorescently-labeled analytes. This technique involves the incorporation of pH-sensitive fluorophores into the composition of the supported lipid bilayer as embedded reporter dyes. It was determined that this assay can operate as either a “turn-on” or a “turn-off” sensor depending on the analyte to be detected. It was additionally found that modulating the ionic strength of the operating buffer allows for tuning the operating pH and sensitivity of the assay. This label-free technique can be utilized to monitor small peptide interactions with bilayers containing specific phospholipids. Basic amino acid sequences which are associated with transporting contents across membranes or anti-microbial activity can be monitored binding to negatively charged bilayers without the use of labels. Not only is this a sensitive technique for detecting small peptides, but thermodynamic data can be extracted as well. In a final set of experiments, the interaction of proteins with phosphatidylserine (PS) in supported lipid bilayers is observed by utilizing PS-Cu2+-induced quenching of fluorophores. Disruption of this metal-phospholipid, specifically by Ca2+-dependent protein kinases, results in a turn-on fluorescent assay, which can be used to monitor the binding of the protein to PS and the effects of other metal interference.

Thesis (Ph. D.)--Washington State University, December 2009. / Title from PDF title page (viewed on Dec. 15, 2009). "Department of Chemistry." Includes bibliographical references (p. 254-266).

Graphene bilayers in Bernal stacking exhibit a transverse electric (E) field dependent band gap, thanks to the on-site electron energy asymmetry between the two layers, which can be used to increase the channel resistivity, and enable higher on/off ratio devices. Using dual-gated device structure, we investigate the transport characteristics of exfoliated graphene bilayers as a function of carrier density and E-field at temperature from 295 K down to 0.3 K. At high E-field, strong conduction suppression near the charge neutrality point is observed, a primary characteristic introduced by band gap opening. The conductivity suppression persists up to the finite threshold voltages, which increase with increasing the E-field, similar to a gapped semiconductor. We extract the transport gap as a function of E-field from the threshold measurement, and further discuss the impact of disorder. At gate bias higher than the threshold, conductivity increases linearly as carrier density increases, which contrasts to the sub-linear dependence in graphene monolayer. Mobility shows decreasing tendency with the increasing E-field, which changes little as temperature changes. Besides, we probe the electrical characteristics of quasi-free-standing graphene bilayers grown on SiC at temperature down to 0.3 K, based on the study on the exfoliated graphene bilayers. The epitaxial graphene bilayer on SiC is prepared by atmospheric pressure graphitization in Ar, followed by H₂ intercalation, which renders the material quasi-free-standing. At the charge neutrality point, the longitudinal resistance shows an insulating behavior, and follows a temperature dependence consistent with variable range hopping transport in a gapped state. Besides, clear linear dependence of the conductivity on the carrier density is observed, which is distinguishable from the sub-linear dependence in graphene monolayer. These properties show that the epitaxial graphene bilayer grown on the SiC exhibits band-gap opening and Bernal stacked arrangement. / text

Thesis (M.S.)--University of Delaware, 2009. / Principal faculty advisor: Sandeep Patel, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

The research presented in this thesis includes the development of designs, materials, and fabrication processes and the results of characterization experiments for a meso-scale hydrogel-based lipid bilayer array system. Two design concepts are investigated as methods for forming Droplet Interface Bilayer (DIB) arrays. Both concepts use a base of patterned silver with Ag/AgCl electrodes patterned onto a flat polymer substrate. In one technique, photopolymerizable hydrogel is cured through a mask to form an array of individual hydrogels on top of the patterned electrodes. The other technique introduces a second type of polymer substrate that physically supports an array of hydrogels using a set of microchannels. This second substrate is fitted onto the first to contact the hydrogels to the electrodes. The hydrogels are used to support and shape droplets of water containing phospholipids, which self-assemble at the surface of the droplet when submerged in oil. Two opposing substrates can then be pushed together, and a bilayer will form at the point where each pair of monolayers come into contact. The photopatterning technique is used to produce small arrays of hydrogels on top of a simple electrode pattern. Systems utilizing the microchannel substrate are used to create mesoscale hydrogel arrays of up to 3x3 that maintained a low resistance (~50-150 kΩ) connection to the substrate. Up to three bilayers are formed simultaneously and verified through visual observation and by recording the current response behavior. Arrays of varying sizes and dimensions and with different electrode patterns can be produced quickly and inexpensively using basic laboratory techniques. The designs and fabrication processes for both types of arrays are created with an eye toward future development of similar systems at the microscale. / Master of Science

Since the rise of multicellular organisms, nature has created a wide range of solutions for life on Earth. This diverse set of solutions presents a broad design space for a number of bio-inspired technologies in many different fields. Of particular interest for this work is the computational and processing power of neurons in the brain. Neuronal networks for transmitting and processing signals have advantages to their electronic counterparts in terms of power efficiency and the ability to handle component failure. In this thesis, an artificial axon system using droplet on hydrogel bilayers (DHBs) in conjunction with alamethicin channels was developed to show properties of action potential signal propagation that occur in myelinated nerve cells. The research demonstrates that the artificial axon system is capable of modifying signals that travel perpendicular to a lipid bilayer interface due to the voltage-gating properties of alamethicin within the connected bilayer. The system was used to show a signal boosting behavior similar to what occurs in the nodes of Ranvier of a myelinated axon. In addition, the artificial axon system was used to show that alamethicin channels within a lipid bilayer behave similarly to slow-acting potassium channels in a real axon in that they follow a sigmoid activation curve in response to a step potential change. / Master of Science

The stimuli response of a polymer – metal bilayer architecture was investigated. This solvent activated system showed a dynamic response when exposed to a particular solvent. Polymer wires were fabricated using a glass capillary array (GCA) as a template. The synthesized wires were then sputtered with silver and exposed to dichloromethane (DCM). The solvent activated response results in a number of physical distortions of which the circular deformation was the most predominant. The thicknesses of the metal coating and the direction of the solvent front were studied in an effort to determine their relationship to the observed wired deformations.