title: Single molecule fluorescence under conditions of fast flow.
abstract: We have experimentally determined the optimal flow velocities to characterize or count single molecules by using a simple microfluidic device to perform two-color coincidence detection (TCCD) and single pair Förster resonance energy transfer (spFRET) using confocal fluorescence spectroscopy on molecules traveling at speeds of up to 10 cm s(-1). We show that flowing single fluorophores at ≥0.5 cm s(-1) reduces the photophysical processes competing with fluorescence, enabling the use of high excitation irradiances to partially compensate for the short residence time within the confocal volume (10-200 μs). Under these conditions, the data acquisition rate can be increased by a maximum of 38-fold using TCCD at 5 cm s(-1) or 18-fold using spFRET at 2 cm s(-1), when compared with diffusion. While structural characterization requires more photons to be collected per event and so necessitates the use of slower speeds (2 cm s(-1) for TCCD and 1 cm s(-1) for spFRET), a considerable enhancement in the event rate could still be obtained (33-fold for TCCD and 16-fold for spFRET). Using flow under optimized conditions, analytes could be rapidly quantified over a dynamic range of up to 4 orders of magnitude by direct molecule counting; a 50 fM dual-labeled model sample can be detected with 99.5% statistical confidence in around 8 s using TCCD and a flow velocity of 5 cm s(-1).
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: Mathew H
authors.initials: MH
authors.lastname: Horrocks
authors.forename: Haitao
authors.initials: H
authors.lastname: Li
authors.forename: Jung-Uk
authors.initials: JU
authors.lastname: Shim
authors.forename: Rohan T
authors.initials: RT
authors.lastname: Ranasinghe
authors.forename: Richard W
authors.initials: RW
authors.lastname: Clarke
authors.forename: Wilhelm T S
authors.initials: WT
authors.lastname: Huck
authors.forename: Chris
authors.initials: C
authors.lastname: Abell
authors.forename: David
authors.initials: D
authors.lastname: Klenerman
mesh_terms: D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D044085:Microfluidics