title: On the performance of bioanalytical fluorescence correlation spectroscopy measurements in a multiparameter photon-counting microscope.
abstract: Fluorescence correlation spectroscopy (FCS) data acquisition and analysis routines were developed and implemented in a home-built, multiparameter photon-counting microscope. Laser excitation conditions were investigated for two representative fluorescent probes, Rhodamine110 and enhanced green fluorescent protein (EGFP). Reliable local concentrations and diffusion constants were obtained by fitting measured FCS curves, provided that the excitation intensity did not exceed 20% of the saturation level for each fluorophore. Accurate results were obtained from FCS measurements for sample concentrations varying from pM to μM range, as well as for conditions of high background signals. These experimental constraints were found to be determined by characteristics of the detection system and by the saturation behavior of the fluorescent probes. These factors actually limit the average number of photons that can be collected from a single fluorophore passing through the detection volume. The versatility of our setup and the data analysis capabilities were tested by measuring the mobility of EGFP in the nucleus of Drosophila cells under conditions of high concentration and molecular crowding. As a bioanalytical application, we studied by FCS the binding affinity of a novel peptide-based drug to the cancer-regulating STAT3 protein and corroborated the results with fluorescence polarization analysis derived from the same photon data.
authors.affiliation: Department of Physics, Institute for Optical Sciences, University of Toronto, Toronto, Canada.
authors.forename: Amir
authors.initials: A
authors.lastname: Mazouchi
authors.forename: Baoxu
authors.initials: B
authors.lastname: Liu
authors.forename: Abdullah
authors.initials: A
authors.lastname: Bahram
authors.forename: Claudiu C
authors.initials: CC
authors.lastname: Gradinaru
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D004330:Drosophila; D005456:Fluorescent Dyes / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000737:chemistry; D009842:Oligopeptides / Q000737:chemistry; D017785:Photons; D011485:Protein Binding; D012235:Rhodamines / Q000737:chemistry; D050796:STAT3 Transcription Factor / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D005456:Fluorescent Dyes; D009842:Oligopeptides; D012235:Rhodamines; D050796:STAT3 Transcription Factor; C485184:enhanced green fluorescent protein; C049025:rhodamine 110; D049452:Green Fluorescent Proteins; C021642:F-chemotactic peptide