Free PDF: Micro-Rheology of Cells and Soft Matter with the NanoTracker™
Introduction
In micro-rheological measurements, the complex deformation or flow of viscoelastic systems under small external forces is investigated. From the dynamic response to well-defined external stress, the mechanical characteristics, i.e. the contributions of viscous and elastic components to the material properties can be derived.
Typically, deformations are in the microscopic range of 0.1 ... 10 µm displacements and sub nN forces on a timescale of milliseconds to seconds.
With the NanoTracker™ optical tweezers setup, spherical particles (beads) with well-defined size and optical properties are used as force sensors and actuators. This ensures the reliability and reproducibility required for mechanical measurements on the smallest scales. For a detailed description of the physical mechanisms underlying optical tapping, please refer to our application note "Quantitative force measurements with optical tweezers: the JPK NanoTracker™ which can be downloaded from www.jpk.com. Briefly, the interaction between focused laser light and the small refractive beads results in optical forces that stably hold the particle in the focal region. Displacements of the particles from their stable position in the harmonic trap potential can be detected by analyzing the transmitted laser light. Once the force constant ("trap stiffness") has been determined in a convinient one-click trap calibration, the displacement data can be converted into units of force. In our fully calibrated NanoTracker™ system, force and displacement of the particle as well as trap position information are recorded at the same time making the relation between force and deformation readily accessible in the acquired data.
This application note describes different types of microrheological measurements that can be performed with the NanoTracker™ optical tweezers system, and the basic principles of their analysis using the integrated data processing software.
For more detailed theoretical background information, please have a look at our technical note "Micro-Rheology Measurements with the NanoTracker™"
