Abstract

Microcantilevers have been investigated as high sensitivity, label free biosensors for approximately 15 years. In nearly all cases, a thin gold film deposited on the microcantilevers is used as an intermediate attachment layer because of the convenience of thiol-gold chemistry. Unfortunately, this attachment chemistry can be unstable when used with complex sample media such as blood plasma. The Nordin group at BYU has recently developed an all-silicon in-plane photonic microcantilever (PMCL) technology to serve as a platform for label-free biosensing. It has the advantage of being readily scalable to simultaneous readout of many PMCLs in array format, and allows integration with polymer microfluidics to facilitate the introduction of biological samples and reagents. An essential processing step for the transformation of the PMCL into a practical biosensor is the ability to effectively immobilize active biological receptors directly on silicon PMCL surfaces such that ligand binding generates sufficient surface stress to cause measureable PMCL deflection. This dissertation presents the development of a method to functionalize the sensor surface of all-silicon in-plane photonic microcantilever (PMCL) arrays. This method employs a materials inkjet printer for non-contact jetting and a fluid that is custom designed for ink-jetting and biological applications with approximately 1 pL droplet size. The method facilitates the application of different receptors on select PMCLs with drop placement accuracy in the +/- 7.5 μm range. The functionalization fluid facilitates further processing using humidity control to achieve full coverage of only the PMCL's top surface and removal of dissolved salts to improve uniformity of receptor coverage and to prevent fouling of the sensor surface. Once a functionalization method was successfully developed, a series of experiments were performed to investigate the amount of surface stress that can be generated when receptors are immobilized directly to the silicon surface. In one series of experiments, a 4.8 μM streptavidin solution was used with biotin immobilized on multiple PMCLs to demonstrate adsorption-induced surface stress and concomitant deflection of the PMCL. The group observed ~ 15 nm PMCL deflection on average, with a corresponding surface stress of approximately 4 mN/m. These experiments yield the sensor response in real-time and employ a combination of multiple PMCLs functionalized as either sensors or unfunctionalized to serve as references. Investigation of various attachment chemistries is included, as well as a comparison with and without passivation of non-sensor surfaces. Investigated passivation strategies prevented ligand binding from generating a differential surface stress. Failure modes and physical mechanisms for adsorption-induced surface stress are discussed. Immobilization and passivation strategies for antibody-based biosensing are demonstrated with fluorescence microscopy and a corresponding PMCL sensing experiment using rabbit anti-goat F(ab') fragments as the receptors and Alex Fluor 488 labeled goat anti-rabbit IgGs as the ligand. While the results of these experiments remain inconclusive, suggestions for future research involving the PMCL sensor array are recommended.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering and Technology; Electrical and Computer Engineering

Rights

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