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. 2021 Jan 25;21(3):795. doi: 10.3390/s21030795

Figure 3.

Figure 3

Mechanism of fluorescent timer, photoactivation, photoconversion and photoswitching. (a) Scheme of monomeric fluorescent timer (FT) and its chromophore structure (box). Slow maturation process (oxidation) of chromophore of FT allows the alteration of emission wavelength alteration over time. (b) Scheme of photoactivatable GFP (PA-GFP) and its chromophore structure (box). Illumination of 405-nm light induces the decarboxylation of the key residue near the chromophore of PA-GFP, transforming the chromophore to be a fluorescent emitting form. (c) Scheme of photoconvertible FP (EosFP) and its chromophore structure (box). Illumination of 405-nm light induces the cleavage of peptide backbone near chromophore, changing the color of emitting fluorescence from green to red. (d) Scheme of photoswitchable FP (Dronpa) and its chromophore structure (box). Illumination of 488-nm light induces cis-to-trans isomerization of chromophore turning off the fluorescence, while 405-nm light reverses it by trans-to-cis isomerization turning on the fluorescence. Highlighting blue, green, red colors on the chromophores display the color of emitting fluorescence, and gray represent non-fluorescent state of chromophore.