Problem statement: Fluorescence microscopy is widely used to image biological specimens. Dyes (or
fluorophores) are added to these samples and irradiated with the appropriate frequency of electromagnetic
radiation and the emitted spectrum is measured. Most of the fluorophores used are dyes that absorb and
emit in UV-Visible regions. These molecules have been used widely to study the cellular structures of most
organisms. However, in the case of mammalian cells, these UV-Visible absorbing molecules possess
strong drawbacks. For example, the signal-to-noise ratio of fluorescent signals for mammalian cells is
significantly less. It is known that mammalian cells are quite transparent in the Near Infrared (NIR) region
of 650-900 nm. Therefore, dyes that absorb and emit in the NIR region are very useful for Near InfraRed
Fluorescence (NIRF) imaging. However, to the best of our knowledge, there is only a handful of dyes that are
fluorescent in the NIR region and many of them are found to be easily photobleachable (the fluorophores lose
their fluorescence due to the excitation by light). Thus, there is a need for dyes that can be easily prepared,
stable, less photobleachable and, absorb and emit strongly in the NIR region.
Project details: Mammalian cells are quite transparent in the NIR region of 650–900 nm, therefore dyes in
this NIR region are very useful for fluorescence imaging. Thus, there is a need for dyes that can be easily
prepared, as well as absorb and emit strongly in the NIR region. BF2-oxasmaragdyrins can absorb in the visible-NIR region and emit in the NIR region. These expanded porphyrins (aromatic macrocyclic compounds) are quite stable under various experimental conditions. The existing NIR fluorescent dyes such as cyanine dyes (IR-780, IR-820 and ICG) are unstable and photobleachable. The NIRF imaging molecules have a significant advantage for imaging in-vitro/ in-vivo mammalian cells due to the less auto-fluorescence in the region of NIR The proposed BF2-oxasmaragdyrin fluorophores and their biomolecular conjugates are highly stable, less photo-bleachable, absorb and emit strongly in NIR region. The functionalized BF2-oxasmaragdyrins can be conjugated readily to biomolecules with specific functions which can be used as targeting agents for fluorescence imaging and photothermal therapy (PTT) for cancer.