Date of Award
Master of Science (MS)
Materials Science and Engineering
Foulger, Stephen H
Ballato , John
Lickfield , Gary
While nuclear imaging techniques (Magnetic Resonance Imaging, Computed Tomography, and Positron Emission Tomography) have proven effective for diagnosis and treatment of disease in the human body, fluorescence-enhanced optical imaging offers additional benefits. Fluorescent imaging provides high resolution with real-time response, persistent lifetime (hours to days), cell targeting, and transdermal penetration with minimal physical encumbrance. Malignant cells can be targeted by absorbance of exogenous fluorescent nanoprobe contrast agents. Imaging is improved by fluorescent enhancement, especially by energy transfer between attached dyes. Also for use against cancer are heat-active treatments, such as hyperthermal, photothermal, and chemothermal therapies. Helpful to these treatments is the thermal response from nanoprobes, within human cells, which provide real-time feedback. The present study investigates the design and feasibility of a nanoprobe molecular device, absorbable into malignant human cells, which provides real-time tracking and thermal response, as indicated by enhanced fluorescence by energy transfer.
A poly(propargyl acrylate) colloidal suspension was synthesized. The particles were modified with a triblock copolymer, previously shown to be thermally responsive, and an end-attached fluorescent dye. A second dye was modeled for attachment in subsequent work. When two fluorescent dyes are brought within sufficiently close proximity, and excitation light is supplied, energy can be transferred between dyes to give enhanced fluorescence with a large Stokes shift (increase in wavelength between excitation and emission). The dye pair was modeled for overlap of emission and absorbance wavelengths, and energy transfer was demonstrated with 23% efficiency and a 209 nm Stokes shift. The quantum yield of the donor dye was determined at 70%, and the distance for 50% energy transfer was calculated at 2.9 nm, consistent with reports for similar compounds.
When the donor/acceptor dye pair is brought within close proximity (Fšrster Resonance Energy Transfer or FRET distance), energy transfer is enabled. The current design is that thermal response of an attached copolymer/dye ligand would cause closer packing of the colloidal particle, resulting in FRET distance for the attached dye pair. The first test of the hypothesis was to track the change in diameter under temperature change. Using Dynamic Light Scattering (DLS), it was shown that the particle diameter decreased from 100 to 82 nm (32 to 44 oC) and then to 60 nm (60 oC). The observed changes correspond with literature and support the hypothesis, that the thermal response and close proximity would enable energy transfer, resulting in the enhanced fluorescence needed as a contrast nanoprobe for hyperthermia treatments.
Bedford, Monte, "Preliminary Investigation into the Design of Thermally Responsive Forster Resonance Energy Transfer Colloids" (2012). All Theses. 1559.