title: A parallel multiharmonic frequency-domain fluorometer for measuring excited-state decay kinetics following one-, two-, or three-photon excitation.
abstract: We report on the performance of a new, multiharmonic frequency-domain instrument that uses the high harmonic content of a passively mode-locked, pulse-picked femto-second Ti-sapphire laser as the excitation source for the determination of one-, two-, or three-photon excited time-resolved fluorescence anisotropy and intensity decay kinetics. In operation, the new instrument can provide a complete frequency-domain data set at 100 modulation frequencies in less than 1 min. The new instrument exhibits 5-10-ps measurement precision and it can rapidly and accurately recover complex excited-state fluorescence anisotropy and intensity decay kinetics under one-, two-, or three-photon excitation for dilute or optically dense samples that exhibit single or multiexponential decay kinetics. This latter aspect of the instrument is demonstrated by successfully determining the excited-state intensity decay kinetics for a dilute aqueous solution of rhodamine 6G dissolved in a high concentration of bromocresol green. This approach is extended by determining the excited-state fluorescence intensity decay kinetics of dilute fluorescein directly in undiluted, whole blood as a function of pH under two-photon excitation conditions. The high-speed capabilities of the new instrument are exploited by performing two-photon excited fluorescence anisotropy decay experiments on the fly for site-selectively labeled bovine serum albumin as it undergoes enzymatic digestion by trypsin.
authors.affiliation: Department of Chemistry, Natural Sciences Complex, State University of New York at Buffalo 14260-3000, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Watkins
authors.forename: C M
authors.initials: CM
authors.lastname: Ingersoll
authors.forename: G A
authors.initials: GA
authors.lastname: Baker
authors.forename: F V
authors.initials: FV
authors.lastname: Bright
mesh_terms: D016880:Anisotropy; D005453:Fluorescence; D005470:Fluorometry / Q000295:instrumentation* / Q000379:methods*; D007700:Kinetics; D017785:Photons