Fluorescence of serotonin in the visible spectrum upon multiphotonic photoconversion

Abstract

The vital molecule serotonin modulates the functioning of the nervous system. The chemical characteristics of serotonin provide multiple advantages for its study in living or fixed tissue. Serotonin has the capacity to emit fluorescence directly and indirectly through chemical intermediates in response to mono-and multiphoton excitation. However, the fluorescent emissions are multifactorial and their dependence on the concentration, excitation wavelength and laser intensity still need a comprehensive study. Here we studied the fluorescence of serotonin excited multiphotonically with near-infrared light. Experiments were conducted in a custom-made multiphoton microscope coupled to a monochromator and a photomultiplier that collected the emissions. We show that the responses of serotonin to multiphoton stimulation are highly non-linear. The well-known violet emission having a 340 nm peak was accompanied by two other emissions in the visible spectrum. The best excitor wavelength to produce both emissions was 700 nm. A green emission with a ∼ 500 nm peak was similar to a previously described fluorescence in response to longer excitation wavelengths. A new blue emission with a ∼ 405 nm peak was originated from the photoconversion of serotonin to a relatively stable product. Such a reaction could be reproduced by irradiation of serotonin with high laser power for 30 minutes. The absorbance of the new compound expanded from ∼ 315 to ∼ 360 nm. Excitation of the irradiated solution monophotonically with 350 nm or biphotonically with 700 nm similarly generated the 405 nm blue emission. Our data are presented quantitatively through the design of a single geometric chart that combines the intensity of each emission in response to the serotonin concentration, excitation wavelengths and laser intensity. The autofluorescence of serotonin in addition to the formation of the two compounds emitting in the visible spectrum provides diverse possibilities for the quantitative study of the dynamics of serotonin in living tissue.

“Synergistic effect” based novel and ultrasensitive approach for the detection of serotonin using DEM-modulated bimetallic nanosheets

“…4A shows three broad bands at 209 nm and 230 nm and a peak at 272 nm. First, the absorption peak increase from 200 nm to 250 nm is due to serotonin 43,44 and the peak is observed at 272 nm for Al–W nanosheets with a small shift. The presence of ST causes the “turn-on” blue fluorescence emission effect at 335 nm after excitation at 300 nm within a few minutes (Fig.…”

Selective recognition of neurotransmitters in aqueous solution by hydroxyphenyl aza-scorpiand ligands

“…In contrast to tryptamine, an analogous compound without the hydroxyl group whose fluorescence increases with the deprotonation of its amine group, the fluorescence intensity of free serotonin shows strong fluorescence quenching above pH 9 related to the deprotonation of the hydroxyl group. [16][17][18] However, in the case of complexed serotonin, this quenching occurs at lower pH values (see Fig. 8).…”

Real-Time Monitoring of Neurotransmitters in the Brain of Living Animals

“…Two-photon imaging uses a fluorophore to absorb two lower-energy photons to reach an excited state, which solves the problem that the excitation wavelength is too short. Two-photon imaging was used to observe the release of dopamine in mouse brain slices by excitation at 540 nm, but neither two-photon nor three-photon imaging can solve the problem of emitted light at ultraviolet wavelengths. , To gain deeper tissue penetration, small-molecule fluorescent probes that chemically react with neurotransmitters were used to indirectly analyze changes in cells or in isolated brain slices. However, the problems of poor light stability and low specificity in the in vivo application were still present.…”