We demonstrate sensitive spatially resolved detection of physiological chromophores that emit in the ultraviolet (<330 nm). An atypical laser source (a visible wavelength femtosecond optical parametric oscillator), and an unconventional collection geometry (a lensless detector that detects the forward-emitted fluorescence) enable this detection. We report the excitation spectra of the catecholamines dopamine and norepinephrine, together with near-UV emitters serotonin and tryptophan, in the range of 550–595 nm. We estimate the molecular two-photon action cross section of dopamine, norepinephrine, and serotonin to be 1.2 mGM (1 GM, or Goppert Mayor, is equal to 10<sup>−58</sup> m<sup>4</sup> s<sup>−1</sup> photon<sup>−1</sup>), 2 mGM, and 43 mGM, respectively, at 560 nm. The sensitivity achieved by this method holds promise for the microscopic imaging of vesicular catecholamines in live cells.
© 2004 Optical Society of America
J. Balaji, Chandra S. Reddy, S. K. Kaushalya, and Sudipta Maiti, "Microfluorometric Detection of Catecholamines with Multiphoton-Excited Fluorescence," Appl. Opt. 43, 2412-2417 (2004)