title: Inexpensive electronics and software for photon statistics and correlation spectroscopy.
abstract: Single-molecule-sensitive microscopy and spectroscopy are transforming biophysics and materials science laboratories. Techniques such as fluorescence correlation spectroscopy (FCS) and single-molecule sensitive fluorescence resonance energy transfer (FRET) are now commonly available in research laboratories but are as yet infrequently available in teaching laboratories. We describe inexpensive electronics and open-source software that bridges this gap, making state-of-the-art research capabilities accessible to undergraduates interested in biophysics. We include a discussion of the intensity correlation function relevant to FCS and how it can be determined from photon arrival times. We demonstrate the system with a measurement of the hydrodynamic radius of a protein using FCS that is suitable for the undergraduate teaching laboratory. The FPGA-based electronics, which are easy to construct, are suitable for more advanced measurements as well, and several applications are described. As implemented, the system has 8 ns timing resolution, can control up to four laser sources, and can collect information from as many as four photon-counting detectors.
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Gamari
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002.
authors.forename: Dianwen
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Buckman
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002.
authors.forename: Peker
authors.initials: P
authors.lastname: Milas
authors.affiliation: AT&T Laboratories Research (ret.), Florham Park NJ, 07932.
authors.forename: John S
authors.initials: JS
authors.lastname: Denker
authors.affiliation: Wadsworth Center, New York State Department of Health, 120 New Scotland Ave, Albany, New York 12208.
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.affiliation: Wadsworth Center, New York State Department of Health, 120 New Scotland Ave, Albany, New York 12208 and Department of Biomedical Sciences, School of Public Health, State University of New York at Albany, P.O. BOX 509, Albany, New York 12201-0509.
authors.forename: Hongmin
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002.
authors.forename: Lori S
authors.initials: LS
authors.lastname: Goldner