Date of Award

6-2012

Degree Name

MS in Biomedical Engineering

Department

Biomedical and General Engineering

Advisor

Dr. Lily Laiho

Abstract

DEVELOPMENT AND CHARACTERIZATION OF PHOSPHOLIPID ENCAPSULATED QUANTUM DOT CONSTRUCTS FOR BIOLOGIC APPLICATIONS

The American Cancer Society predicts that 577,190 cancer-related deaths and 1,638,910 newly diagnosed cases of cancer will occur in 2012. As these statistics show, cancer is a prevalent and devastating health issue; determined by the Mayo Clinic to be the second leading cause of death in the United States. Skin cancer is the most common form of cancer in the United States. In 2012 more than 68,000 Americans will be diagnosed with melanoma, 48,000 will be diagnosed with an early form of the disease that has not yet reached the lower levels of the epidermis, and more than 2 million people will be treated for basal cell or squamous cell skin cancer. Early and accurate detection is the most reliable way to ensure a positive outcome and the ultimate survival of the patient. As the most aggressive form of skin cancer, survival of melanoma is especially connected to early detection. Current methods for the initial detection of potential cancerous masses and lesions rely on visual examination, palpitation, and biopsy. Accurate determination of the presence of cancerous cells in a biopsy is especially difficult at the early stages when only a small percentage of cells in the biopsied mass show the morphological traits associated with being cancerous. This circumstance often results in a false negative (FN), delaying the necessary treatment until the cancer has reached a more developed stage. Developing more accurate methods for the detection of cancerous cells within a biopsy would aid in alleviating this problem. An improvement to the conventional method of visually examining biopsied tissues for the presence of cells with abnormal morphologies can be offered by utilizing the model of functionalized quantum dot (QD) constructs.

Quantum dots are nano-particles composed of semi-conducting materials that fluoresce at discrete wavelengths when irradiated by a high energy UV source. QD constructs are cadmium-selenium/zinc-sulfide (CdSe/ZnS) quantum dots encapsulated within a bovine derived milk phospholipid micelle. QD constructs provide a potential mechanism for the identification of cancerous cells within a biopsy. Appreciating the scope of the clinical problem and understanding the potential of QDs, the objective of this thesis is to develop a primary model for the solubilization, encapsulation, and primary phospholipid functionalization of two distinct sizes of CdSe/ZnS QDs. The first stage of this thesis optimized the currently utilized protocol for synthesizing cadmium-selenium (CdSe) quantum dots to develop a set of parameters for consistently producing white fluorescing CdSe cores (WFCs) and CdSe/ZnS QDs of 505nm and 555nm (+/- 10nm). The application of synthesis times, temperatures, and quenching methods were employed to achieve this. The second stage developed a phospholipid encapsulation method for the initial functionalization and suspension of the hydrophobic QDs in aqueous media via encapsulation within phospholipid micelles. The final stage of this thesis focused on the successful introduction of the QD constructs into keratinocyte cells. Calcein and Ethidium homodimer-1 stains were applied to determine cell viability, Histochoice was applied as a fixative, and Hoechst staining was employed for cell nuclei identification. Analysis using confocal microscopy suggests successful attachment of QD constructs, in 0.1% w/v keratinocyte media, to the exterior of keratinocyte cell membranes with a 30% average cell survival rate at 24 hours after sample introduction. Future research investigating the interaction of QD constructs with biologic mediums of greater physiological complexity, as well as application of a secondary functionalization, are the next steps on the path toward achieving a viable mechanism for targeting and identifying cancerous cells within a biopsy.

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