Seeing\nand Cleaving: Turn-Off Fluorophore Uncaging\nand Its Application in Hydrogel Photopatterning and Traceable Neurotransmitter\nPhotocages

The advancements\nin targeted drug release and experimental neuroscience\nhave amplified the scientific interest in photolabile protecting groups\n(PPGs) and photouncaging. The growing need for the detection of uncaging\nevents has led to the development of reporters with fluorescence turn-on\nupon uncaging. In contrast, fluorescent tags with turn-off properties\nhave been drastically underexplored, although there are applications\nwhere they would be sought after. In this work, a rhodamine-based\nfluorescent tag is developed with signal turn-off following photouncaging.\nOne-photon photolysis experiments reveal a ready loss of red fluorescence\nsignal upon UV (365 nm) irradiation, while no significant change is\nobserved in control experiments in the absence of PPG or with irradiation\naround the absorption maximum of the fluorophore (595 nm). The two-photon\nphotolysis of the turn-off fluorescent tag is explored in hydrogel\nphotolithography experiments. The hydrogel-bound tag enables the power-,\ndwell time-, and wavelength-dependent construction of intricate patterns\nand gradients. Finally, a prominent caged neurotransmitter (MNI-Glu)\nis modified with the fluorescent tag, resulting in the glutamate precursor\nnamed as GlutaTrace with fluorescence traceability and turn-off upon\nphotouncaging. GlutaTrace is successfully applied for the visualization\nof glutamate precursor distribution following capillary microinjection\nand for the selective excitation of neurons in a mouse brain model.