PhD Proposal Defense

Fluorophore has been extensively used in biosensing and bioimaging for disease diagnosis and prognosis. For fluorophore mediated biosensing and bioimaging, artificial alteration of fluorescence (enhancement/quenching) can be highly beneficial for improving sensitivity and contrast. Certain type of nanoparticles, including nanogold particles (NGPs), can increase or decrease the fluorescence of fluorophores by their strong surface plasmon polariton field (SPPF). The intensity of the SPPF depends on metal type, particle size, and the distance from the particle. SPPF is the maximum at the particle surface and decays exponentially away from the surface. Therefore, when the metal type and particle size are fixed, the fluorescence alteration can be controlled by manipulating the distance from a fluorophore to a particle.

We have been utilizing NGPs to enhance the sensitivity of our fluorophore mediated biosensing system. Some solvents were also found to enhance fluorescence. Ethanol and butanol were found very effective for our sensing system, without denaturing biomolecules on the sensor surface. The performances of NGPs in ethanol or butanol will be compared in terms of their assay time, consistency, and enhancement level. The one showing better performance will be selected, and the sensing procedure for our biomarkers (four cardiac markers) will be finalized.

Combining both fluorescence quenching and enhancement properties by NGP can create a novel optical contrast agent for molecular imaging. In this agent, the fluorescence is manipulated by linking a fluorophore to an NGP with double linkers, one is long for fluorescence enhancement, and the other is short for quenching, and also contains a structure cleavable by disease specific biomolecule. This agent conditionally emits fluorescence only at a particular disease site, at an enhanced fluorescence level. Initial studies have been performed on the dependence of fluorescence alteration on the distance between a fluorophore and an NGP. The fluorescence quenching or enhancement was observed when fluorophore was linked to an NGP via a short or a long spacer, respectively. The feasibility of the short linker with the cleavable site was demonstrated. The lengths of short linker and long linker will be optimized, the fluorophore will be conjugated to NGP via both linkers, and a disease targeting molecule will also be conjugated to NGP. The final product will be tested using animal cell lines.