title: Multiphoton-excited fluorescence of fluorogen-labeled neurotransmitters.
abstract: Fluorescence detection of fluorogen-labeled neurotransmitters is demonstrated using 100 fs pulses from a titanium-sapphire mode-locked laser to achieve molecular excitation by simultaneous absorption of two and three photons of near-IR radiation. Two-photon excitation spectra are determined for the naphthalene-2,3 dicarboxaldehyde derivative of glycine and the fluorescamine derivative of leucine enkephalin, with the peak excitation cross section (o2) approximately equal to 1 x 10(-50) cm4 s/photon for both species. Three-photon-excitation fluorescence is demonstrated for o-phthaldialdehyde-labeled glutamate using excitation wavelengths between 965 and 1012 nm. The three-photon excitation cross section (o3) remains nearly constant in this wavelength range, with an absolute value of approximately 10(-84)-10(-85) cm6 s2/photon 2. Rapid cycling of analytes through the fluorescent excited state and detection that is free from background caused by Rayleigh and Raman scatter combine to make multiphoton-excited fluorescence a highly sensitive approach for detecting trace amounts of neurotransmitters. Measurements of two-photon-excited fluorescence of fluorescamine-labeled bradykinin and analysis of multiphoton-excited background reveal the potential of this method to detect fewer than 1000 neurotransmitter molecules.
authors.affiliation: Cornell University, Ithaca, New York 14853, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Shear
authors.forename: E B
authors.initials: EB
authors.lastname: Brown
authors.forename: W W
authors.initials: WW
authors.lastname: Webb
mesh_terms: D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents / Q000032:analysis*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013055:Spectrophotometry, Infrared / Q000379:methods
chemical_list: D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents