Graduation Year

2011

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Nathan D. Gallant

Co-Major Professor

Rasim O. Guldiken

Keywords

3-APTMS, Bcl-2 Protein, ODMS, Pluronic, Protein A/G

Abstract

Ovarian cancer is the fifth leading cause of cancer death among women in United States and has an alarming 1.4% (1 in 71) lifetime risk. The lack of overt symptoms and the absence of a reliable screening test to detect ovarian cancer result in over 70% of women being diagnosed after the disease has spread beyond the ovary resulting in a poor prognosis. A key characteristic of ovarian cancer is the ability of tumor cells to evade apoptosis, or programmed cell death contributing to the limitless replicative potential, which is a hallmark of all carcinogenesis. There is conclusive evidence that levels of bcl-2 are elevated in ovarian cancer patients' indication that this protein is an ovarian cancer biomarker. The overall goal of this thesis is to functionalize a substrate for specific, sensitive and cost-effective bcl-2 capture. This surface will ultimately be incorporated into an acoustic wave-based diagnostic device for worldwide point-of-care (POC) ovarian cancer detection.

This research looks to assess the capture of this analyte protein on a series of bioconjugated surfaces. For the research to be diagnostically applicable, certain factors reveal themselves as more important than others. Since the surface-bound capture antibody must recognize the bcl-2 protein, it is vital to ensure upright orientation of this specific antibody with high affinity for the analyte. Furthermore once integrated with a nanosensor, the surface will sense a change in the mass on the surface, which requires that the surface is highly resistant to non-specific binding. Bioconjugation techniques were employed to initiate self-assembled monolayers (SAM) of silanes, immobilize antibodies (via amine-crosslinking or direct adsorption of protein A/G) and disperse polyethylene glycol (PEG) reagents to reduce non-specific binding on the glass substrates. 3-aminopropyltrimethoxysilane (3-APTMS) and chlorodimethyloctylsilane (ODMS) were deposited on the surface to create initial hydrophilic and hydrophobic properties on which molecular self-assembly could occur. Testing a variety of assemblies with and without the presence of silanes, amine-crosslinking and PEGylation reagents, the substrate displaying the highest efficacy of bcl-2 capture was revealed. These various surfaces were assessed through contact angle and a novel sandwich enzyme linked immunosorbent assay (ELISA) for sensitivity and specificity of bcl-2 standard capture.

The consistently low background and facile assembly of the ODMS based substrate with direct adsorption of protein A/G and the PEGylation reagent, Pluronic, was deemed the best functionalized surface for non-specific recruitment of the bcl-2 protein. The substrate also consistently displayed low signal-to-noise ratio which was of extreme importance in this research to guarantee the prevention of false-positive results when detecting nascent carcinogenic behavior. Elucidation of this substrate assembly is the first step towards the long term objective of this thesis, which is to construct a cost-effective early ovarian cancer detection device which can be implemented at the point-of-care to those who need it the most. This is ultimately expected to dramatically improve health outcomes for females worldwide.

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