Nikita Kumari

Nikita Kumari, Arizona State University (Graduate Student)

Diving Deep into the Red: Novel Cyanine Dyes for Super-Resolution Imaging

Fluorescent probes help biologists illuminate the inner workings of cancer cells. In this work, we study the photophysical properties of a novel class of far-red fluorescent probes that could allow live tissue to be imaged in greater depth and detail than is possible with current techniques. One of the limitations for super-resolution fluorescence microscopy techniques is the low brightness of the fluorophore which dictates signal-to-noise ratio for the fluorescence detection. The low brightness of the fluorophore could be because of various non-radiative decay pathways from the excited state to the ground state of the molecule which competes with the radiative pathway, decreasing the fluorescence quantum yield. The most prominent non-radiative pathway for cyanine fluorophores is the ability of an excited-state electron to go from trans (fluorescent form) to cis (non-fluorescent) state which is known as photoisomerization. We attempt to eliminate this trans-cis photoisomerization to happen by rigidifying the backbone of the cyanine. We applied this strategy on pentamethine cyanine dye which is a far-red cyanine fluorophore. The photophysical characterization of the newly synthesized restricted dye in comparison to traditional pentacyanine showed that the installation of the ring system restricts the photoisomerization, showed by temperature-independent emission, and solvent viscosity independent properties. The resulting molecule exhibit the characteristic features of conformational restraint, including improved fluorescence quantum yield and extended lifetime. The new rigidified molecule was found to have desired photophysical properties and improved the quality of super-resolution image obtained.