Open AccessDifferential interferometric particle tracking on the subnanometer- and submillisecond-scale
Author(s) -
Dennis Müller,
Dieter R. Klopfenstein,
R. G. Ulbrich
Publication year - 2013
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.21.007362
Subject(s) - optics , interferometry , microscope , physics , tracking (education) , particle tracking velocimetry , particle (ecology) , image resolution , temporal resolution , microscopy , laser , materials science , particle image velocimetry , psychology , pedagogy , turbulence , oceanography , thermodynamics , geology
We describe an interferometric method to measure the movement of a subwavelength probe particle relative to an immobilized reference particle with high spatial (Δx = 0.9nm) and temporal (Δt = 200μs) resolution. The differential method eliminates microscope stage drift. An upright microscope is equipped with laser dark field illumination (λ(0) = 532nm, P(0) = 30mW) and a compact modified Mach-Zehnder interferometer is mounted on the camera exit of the microscope, where the beams of scattered light of both particles are combined. The resulting interferograms provide in two channels subnanometer information about the motion of the probe particle relative to the reference particle. The interferograms are probed with two avalanche photodiodes. We applied this method to measuring the movement of kinesin along microtubules and were able to resolve the generic 8-nm steps at high ATP concentrations without external forces.