Graduation Year

2009

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biomedical Engineering

Major Professor

Sergei Ostapenko, Ph.D.

Co-Major Professor

John T. Wolan, Ph.D.

Keywords

Spectral shift, Biomarkers, Prostate specific antigen, ELISA, Agarose gel electrophoresis

Abstract

Most of the bio-applications of semiconductor quantum dots (QDs) show and utilize their superior optical properties over organic fluorophores. An estimated 3-35% of all cancer deaths could be avoided through early detection, therefore, there is a critical need to develop sensitive probes. The objectives of this work are: Research the phenomena of "blue" photoluminescence (PL) spectral shift on the dried bioconjugated QDs and develop the relevant mechanism; Develop a methodology that will allow successful confirmation of the bioconjugation reaction between biomolecules and QDs; Propose a modification of an existent method or approach to employ the "blue" spectral shift of bioconjugated QDs for early cancer detection. Results indicated that the "blue" spectral shift, observed for dried on the silicon substrates bioconjugated QDs, is increased with the time of storage and reaches 30-40nm in 14 days.

It is accelerated at elevated temperatures and slowed down at lower temperatures. Larger size QDs generate spectral shifts of larger magnitudes, and the spectral shift is positively correlated with the biomolecule's size/weight. This phenomenon is explained by elastic and compression stress due to nonhomogenious drying of the QD droplet and the reaction with the solid surface. Agarose gel electrophoresis technique, optimized with organic dye fluorescamine, is suitable for bioconjugation verification. The optimal running parameters were found to be 2% agarose gel, 1.5V working voltage, 0.5X TBE as a running buffer, and about 120 mins running time. The spectral shift was implemented for improving the sensitivity of Prostate Specific Antigen (PSA) Enzyme-Linked ImmunoSorbent Assay (ELISA). It was found that QD ELISA could be as much, as 100 times more sensitive than the regular commercial ELISA, based on the enzymatic detection.

The results of this work show that QDs may be very useful for early detection of several types of cancers, including prostate cancer in men and breast/ovarian/uterine cancers in women.

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