Optical Tweezes with Video-Based Force Detection


Overview

•    Single or dual beam optical tweezers system based on an inverted microscope
•    3D real-time video-based force measurements with sub-pN resolution
•    Huge free space above optical trap for all kinds of sample chambers and carriers
•    Manipulate and navigate trapped objects with nanometer precision
•    Easily extendable to fluorescence, STED, Raman spectroscopy, TIRF, or CLS
•    Compact and ultrastable modular design
•    No detector adjustments required
•    Fast, easy, and reliable force calibration
•    Customizable LabViewTM interface


Applications

There is a wide field of applications that includes the investigation of single molecules and motor proteins, receptor-ligand-interactions, intramolecular elasticity, protein folding and unfolding, and controlled nanopore translocations. Polymer elasticity or DNA overstretching phenomena can be scrutinized in detail. Interactions on artificial or natural membranes like cell surfaces can be analyzed and trapping of individual particles inside living cells is possible. Last, but not least the Brownian motion of microscopic particles in various environments, tracking of particles and rheological surveys (e.g. inside of microfluidic devices) are some of many further applications.


The Optical Trap

Microscopic objects - like individual nano-or microparticles, cells, bacteria, cell compartments, or clustered molecules - can be trapped securely inside the center of a strongly focused laser beam. When an external force is acting on the trapped object, it deflects from the center of the trap. The deflection depends linearly on trap stiffness and force.


Forces

Any trapped object experiences various external forces: Atoms or molecules of the surrounding medium induce Brownian motion in all three dimensions, depending on temperature, viscosity and the presence of obstacles in proximity. Macroscopic fluid movements cause drag forces. Electric fields, bulk or surface charges may generate electrophoretic or electroosmotic forces, too. Particularly, single molecules bound to a trapped object can induce forces of broad variety and magnitude. The application of a force generated by an optical trap to a single molecule will gain vast insights into its molecular structure and elasticity, binding properties and kinetics.


Force measurement

Generating and metering various forces requires a reliable force measurement capability in all three dimensions to allow for a maximum degree of experimental accuracy and versatility. Thus, force detection must be accomplished by precisely measuring the deflection of the trapped particle in each dimension. PicoTweezers utilizes a sophisticated and easy-to-use video analysis for particle detection, tracking and force measurements. It provides the largest field of application since it avoids common optical tweezers’ calibration difficulties, system instabilities, as well as experimental and spatial restrictions.
The entire video detection is integrated into the optical pathway underneath the optical trap. Since the diameter of the trapped object is permanently monitored, any objects of interest can be trapped or compared with previous ones on demand. Video detection is unsusceptible to disturbing particles that occasionally may be trapped together with the measured object. When trapping objects close to interfaces (bottom or ceiling of a sample chamber, artificial or biological membranes, etc.), only video analysis delivers an interference-free force signal.

Publications

A. Sischka, L. Galla, A.J. Meyer, A. Spiering, S. Knust, M. Mayer, A.R. Hall, A. Beyer, P. Reimann, A. Gölzhäuser, and D. Anselmetti: Controlled Translocation of DNA Through Nanopores in Carbon Nano-, Silicon-Nitride- and Lipid-Coated Membranes. Analyst, 140, 4843 (2015)

T. Jany, A. Moreth, C. Gruschka, A. Sischka, A. Spiering, M. Dieding, Y. Wang, S. Haji Samo, A. Stammler, H. Boegge, G. Fischer von Mollard, D. Anselmetti, and T. Glaser: Rational Design of a Cytotoxic Dinuclear Cu-2 Complex That Binds by Molecular Recognition at Two Neighboring Phosphates of the DNA Backbone. Inorganic Chemistry, 54, 2679 (2015)

L. Galla, A.J. Meyer, A. Spiering, A. Sischka, M. Mayer, A.R. Hall, P. Reimann, and D. Anselmetti: Hydrodynamic Slip on DNA Observed by Optical Tweezers-Controlled Translocation Experiments with Solid-State and Lipid-Coated Nanopores. Nano Letters, 14, 4176 (2014)

S. Knust, A. Spiering, H. Vieker, A. Beyer, A. Gölzhäuser, K. Tönsing, A. Sischka, and D. Anselmetti: Video-Based and Interference-Free Axial Force Detection and Analysis for Optical Tweezers. Review of Scientific Instruments, 83, 103704 (2012)