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Title: | Engineering Functional Interfaces for Biosensing, Minimization of Protein Adsorption, and Structural Self-Healing |
Authors: | Deng, Xudong |
Advisor: | Filipe, Carlos Hoare, Todd |
Department: | Chemical Engineering |
Publication Date: | 2016 |
Abstract: | This thesis describes strategies on how to efficiently modify biological interfaces either effectively to reduce nonspecific protein binding in various contexts or to encourage specific interfacial interactions following exposure to a ligand or following the disruption of a biomaterial. Nonspecific protein adsorption at interfaces is a significant issue in the development of robust biosensors and implantable biomaterials, and modifying surfaces to achieve this goal is currently a complicated and relative inefficient process. On the other hand, current protein immobilization methods, including physical and covalent attachment, can interfere with specific binding sites, thus reducing the efficiency of bio-recognition events and resulting in a loss of specific binding potential that, for example, significantly compromises biosensor performance. In addition to the protein binding, dynamic interfacial interactions are sometimes desirable to allow for rapid and reversible responses to external stimuli when particular applications are targeted. In this thesis, I report on new approaches for efficient protein passivation and immobilization as well as a new type of self-healing hydrogel that can serve as platforms for the development of functional biosensors and biomaterials. In the first part of the thesis, a simple, scalable procedure to passivate paper against non-specific protein adsorption is introduced. This method is based on a simple sequential dipping protocol inspired by the polyelectrolyte layer-by-layer approach, but instead using covalently reactive hydrazide and aldehyde-functionalized poly(oligoethylene glycol) oligomers (both of which can be easily synthesized via one or two-step chemistries). This sequential dipping method creates a thin hydrogel layer around the cellulose fibers within the paper network without affecting the fiber morphology or macropore network of the paper that effectively lowered non-specific adsorption of a broad range of proteins to the paper by at least one order of magnitude. This method was subsequently applied in the fabrication of paper-based microfluidic sensors that enable protein transport in lateral flow assays as well as paper-based enzyme-linked immunosorbent assays (ELISAs) that exhibit both lower limits of detection and higher dynamic ranges relative to papers blocked with the conventional blocking agents. The simplicity of this surface modification method has great potential to be applied in various paper-based biosensors or for coating other porous media (e.g. membranes) to counteract biofouling. The next part of this thesis was dedicated to developing a simple, mixing-based protocol for conjugating hyaluronic acid (HA) on the surface of a contact lens, again using hydrazone chemistry to perform the coupling. This simple conjugation method, based on a two-step preparation technique consisting of laccase/TEMPO-mediated oxidation of the surface of poly(2-hydroxyethyl methacrylate) (PHEMA)-based contact lenses followed by covalent grafting of hydrazide-functionalized HA via simple immersion, can be achieved under ambient conditions without the need for any external crosslinkers or energy. The resulting lenses were significantly more wettable, more water-retentive, and less prone to protein adsorption than the native lenses, all of which are key factors in improving the comfort and functionality of the lens for a patient. These characteristics were achieved without causing any significant changes in terms of the transparency, refractive index, or key mechanical properties of the lens. The third part of this thesis describes a new approach for performing highly sensitive immunosorbent assays by combining the adsorption capacity of graphene oxide with the high sensitivity of the quartz crystal microbalance (QCM). Specifically, by functionalizing graphene oxide with biotin and subsequently complexing with avidin, the irreversible adsorption of graphene oxide to the surface of a gold QCM biosensor is used as a linking layer for functionalizing a QCM sensor with antibodies. Given the broad availability of multiple types of biotinylated capture antibodies, such an interface provides a flexible substrate for performing a variety of immunoassays of interest. Furthermore, the whole immunoassay process takes less than 5 hours, faster than (or at least comparable with) other approaches that are practically and chemically more complex. As a proof-of-concept, rabbit IgG at concentrations ranging from 0.1 ng/mL to 10 μg/mL (six orders of magnitude) could be quantitatively detected with high sensitivity and selectivity. Finally, I developed a new method to prepare fast self-healing hydrogels from hyaluronic acid and poly(vinyl alcohol), exploiting the dynamic crosslinking of boronate esters at both neutral and acidic pH. The hydrogel underwent fast (<1 minute) and effective self-healing in both macroscopic cleave/heal tests and microscopic rheological shear tests, providing a hydrogel scaffold with dynamic crosslinking capability over a broad pH range relevant to physiological applications. Overall, these fabrication techniques can be widely used for the simple and scalable preparation of stable, functional and unique biological interfaces for both therapeutic and diagnostic applications. |
URI: | http://hdl.handle.net/11375/20437 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Deng_Xudong_201608_PhD.pdf | PhD Thesis of Xudong Deng | 9.55 MB | Adobe PDF | View/Open |
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