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Measuring Piconewton Forces by Optical tweezers (OT) (CAT#: STEM-MB-1283-WXH)

Introduction

Optical tweezers instruments use the forces of laser radiation pressure to trap small particles. Using various techniques, these trapped particles can then be manipulated and forces on the objects in the trap can be measured. The forces that such an instrument is capable of measuring are of the order of one to 100 piconewtons (pN).




Principle

Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner similar to tweezers. If the object is held in air or vacuum without additional support, it can be called optical levitation.
The laser light provides an attractive or repulsive force (typically on the order of piconewtons), depending on the relative refractive index between particle and surrounding medium. Levitation is possible if the force of the light counters the force of gravity. The trapped particles are usually micron-sized, or even smaller. Dielectric and absorbing particles can be trapped, too.

Applications

• Optical tweezers are used in biology and medicine (for example to grab and hold a single bacterium, a cell like a sperm cell or a blood cell, or a molecule like DNA).
• Nanoengineering and nanochemistry (to study and build materials from single molecules).
• Quantum optics and quantum optomechanics (to study the interaction of single particles with light).

Procedure

1.Sample preparation
2.Force Calibration
3.Measurement
4.Analysis

Materials

Optical tweezers