Application Notes

DNA Translocation Through Nanopores

Single Molecules and
DNA Elasticity


Technical Notes

Optical Trapping and Force Measurement


Force Sensitive Optical Tweezers

General Aspects of PicoTweezers
•    Single or dual beam stand-alone optical tweezers system
•    Free space above optical trap for all kinds of sample chambers and carriers
•    3D video-based force measurements with sub-pN resolution (550 Hz sample rate)
•    Manipulation of trapped objects with nanometer precision
•    Compact and ultrastable modular design, integrated into an inverted microscope
•    No detector alignment or adjustment required before or during experimentation
•    Very fast, easy, and reliable force calibration
•    Customizable LabViewTM interface
•    Easily extendable to fluorescence, Raman spectroscopy, CLS, TIRF, or STED

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.

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 between laser and 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.

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)