Particle tracking by repetitive phase-shift interferometric super resolution microscopy

Accurate and rapid particle tracking is essential for address-ing many research problems in single molecule and cellular biophysics and colloidal soft condensed matter physics. We developed a novel three-dimensional interferometric fluo-rescent particle tracking approach that does not require any sample scanning. By periodically shifting the interfer-ometer phase, the information stored in the interference pattern of the emitted light allows localizing particles posi-tions with nanometer resolution. This tracking protocol was demonstrated by measuring a known trajectory of a fluorescent bead with sub-5 nm axial localization error at 5 Hz. The interferometric microscopy was used to track the RecA protein in Bacillus subtilis bacteria to demonstrate its compatibility with biological systems.