title: Label-Free Imaging of Single Microtubule Dynamics Using Spatial Light Interference Microscopy.
abstract: Due to their diameter, of only 24 nm, single microtubules are extremely challenging to image without the use of extrinsic contrast agents. As a result, fluorescence tagging is the common method to visualize their motility. However, such investigation is limited by photobleaching and phototoxicity. We experimentally demonstrate the capability of combining label-free spatial light interference microscopy (SLIM) with numerical processing for imaging single microtubules in a gliding assay. SLIM combines four different intensity images to obtain the optical path length map associated with the sample. Because of the use of broadband fields, the sensitivity to path length is better than 1 nm without (temporal) averaging and better than 0.1 nm upon averaging. Our results indicate that SLIM can image the dynamics of microtubules in a full field of view, of 200 × 200 μm2, over many hours. Modeling the microtubule transport via the diffusion-advection equation, we found that the dispersion relation yields the standard deviation of the velocity distribution, without the need for tracking individual tubes. Interestingly, during a 2 h window, the microtubules begin to decelerate, at 100 pm/s2over a 20 min period. Thus, SLIM is likely to serve as a useful tool for understanding molecular motor activity, especially over large time scales, where fluorescence methods are of limited utility.
authors.affiliation: Quantitative Light Imaging Laboratory, Department of Electrical and Computer Engineering, Beckman Institute of Advanced Science and Technology, ‡Center for the Physics of Living Cells, §Center for Biophysics and Quantitative Biology, ∥Department of Physics, and ⊥Department of Bioengineering, University of Illinois , Urbana, Illinois 61801, United States.
authors.forename: Mikhail E
authors.identifier: 0000-0003-2124-7750
authors.initials: ME
authors.lastname: Kandel
authors.affiliation: Quantitative Light Imaging Laboratory, Department of Electrical and Computer Engineering, Beckman Institute of Advanced Science and Technology, ‡Center for the Physics of Living Cells, §Center for Biophysics and Quantitative Biology, ∥Department of Physics, and ⊥Department of Bioengineering, University of Illinois , Urbana, Illinois 61801, United States.
authors.forename: Kai Wen
authors.initials: KW
authors.lastname: Teng
authors.affiliation: Quantitative Light Imaging Laboratory, Department of Electrical and Computer Engineering, Beckman Institute of Advanced Science and Technology, ‡Center for the Physics of Living Cells, §Center for Biophysics and Quantitative Biology, ∥Department of Physics, and ⊥Department of Bioengineering, University of Illinois , Urbana, Illinois 61801, United States.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Selvin
authors.affiliation: Quantitative Light Imaging Laboratory, Department of Electrical and Computer Engineering, Beckman Institute of Advanced Science and Technology, ‡Center for the Physics of Living Cells, §Center for Biophysics and Quantitative Biology, ∥Department of Physics, and ⊥Department of Bioengineering, University of Illinois , Urbana, Illinois 61801, United States.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Popescu
mesh_terms: D000818:Animals; D004058:Diffusion; D008857:Microscopy, Interference / Q000379:methods*; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism*; D061848:Optical Imaging; D010316:Particle Size; D013499:Surface Properties; D013552:Swine; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism
chemical_list: D014404:Tubulin
keywords: cellular cytoskeleton; high-sensitivity detection; label-free; microscopy; microtubules; quantitative phase imaging; single particle imaging