Dense and Acidic Organelle-Targeted Visualization in Living Cells: Application of Viscosity-Responsive Fluorescence Utilizing Restricted Access to Minimum Energy Conical Intersection

06 February 2023, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Cell-imaging methods with functional fluorescent probes are an indispensable technique to evaluate physical parameters in cellular mi-croenvironments. In particular, molecular rotors, which take advantage of the twisted intramolecular charge transfer (TICT) process, have helped evaluate microviscosity. However, the involvement of charge-separated species in the fluorescence process potentially limits the quantitative evaluation of viscosity. Herein we developed viscosity-responsive fluorescent probes for cell imaging that are not depend-ent on the TICT process. We synthesized AnP2-H and AnP2-OEG, both of which contain 9,10-di(piperazinyl)anthracene, based on 9,10-bis(N,N-dialkylamino)anthracene that adopt a non-flat geometry at minimum energy conical intersection. AnP2-H and AnP2-OEG exhibited enhanced fluorescence as the viscosity increased, with sensitivities comparable to those of conventional molecular rotors. In living cell systems, AnP2-OEG showed low cytotoxicity and, reflecting its viscosity-responsive property, allowed specific visualization of dense and acidic organelles such as lysosomes, secretory granules and melanosomes under washout-free conditions. These results provide a new direction for developing functional fluorescent probes targeting dense organelles.

Keywords

Viscosity Sensitive Probe
Lysosome
MECI
Fluorescent Probe
Secretory Granule
Melanosome

Supplementary materials

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Supporting Information
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Details of synthesis, characterization, acid-base titration, fluorescence studies, and microscopic studies.
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