SYNTHESIS AND DEVELOPMENT OF FLUORESCENT CARBON DOTS FOR SENSING AND BIOIMAGING APPLICATIONS

Abstract

Carbon dots (CDs) are the newest class of nanocarbon family with fluorescent properties. CDs are promising candidates to replace traditional toxic semiconductor quantum dots due to their biocompatibility, low cytotoxicity, simple synthesis routes using cheap starting materials, excellent water solubility, and tunable optical properties. This dissertation describes three projects, that are related to the design, synthesis, and characterization of different fluorescent CDs for metal ion sensing and bioimaging applications. One challenge in the field of CDs is synthesizing CDs with high photoluminescence quantum yields (QY) from commonly available reagents. Thus, CDs were designed and synthesized from citric acid and urea, a common CD formulation, but doing so in the presence of Tween®80 and by a hydrothermal microwave method which yielded CDs with a QY=75.5%. This is one of the highest QY values for CDs reported to date, and these CDs can selectively detect Fe2+/Fe3+ ions among other metal ions, which make them a promising candidate for water quality analysis applications. The second project sought to understand differences in how aliphatic, cycloaliphatic and aromatic diamines influence nitrogen doped CDs properties. In this systematic study, nitrogen-doped (N-doped) CDs from 1,6-Hexamethylenediamine (HMD), trans-1,4-Cyclohexanediamine (CHD), and para-Phenylenediamine (pPD), while maintaining the C:N mole ratio at 6:2, so only the carbon structure around the N was changed. We then measured the optical and other effects on the CDs prepared from these different amines. The third investigation used the main findings of studies 1 and 2, to prepare new CDs that might have value as effective fluorescence probes in cancer research. We used citric acid and Tween®80 as before and used tris(hydroxymethyl) methyl aminomethane (Tris) in place of urea. Tris is a more basic and reactive aliphatic amine than urea. This formulation was then used to prepare nitrogen-doped CDs for the selective detection of cancer cells. Based on laser scanning confocal imaging results, these dots effectively labeled MCF-7 breast cancer cells when tested against healthy Human Dermal Fibroblasts, Adult (HDFa) cells as controls. The use of Tween®80 increases the surface amount of polar groups, which are critical for higher cellular uptake of CDs in cancer cells.