OPTICAL TWEEZERS: THE

FORCE OF LIGHT

Introduction

General description

Working

Vedio of traping particle

Diagrams of instrument

Application

INTRODUCTIONOptical tweezers:

Light can exert forces on small

dielectric objects1, A tightly focused

beam of light can trap micron-sized

objects, such as latex beads. This

“optical trapping” principle has found

many applications in chemistry, physics

and biology. It has found its most

prominent use in biophysics, because it

allows the manipulation (like with a

tweezers) of single biomolecules. For

example, “optical tweezers” have been

used to measure the elasticity

OPTICAL TWEEZERS ?An optical tweezer is a scientific instrument thatuses a focused laser beam to provide an attractiveor repulsive force, depending on the index mismatch(typically on the order of piconewtons) to physicallyhold and move microscopic dielectric objects. Opticaltweezers have been particularly successful instudying a variety of biological systems in recentyears.Dielectric objects are attracted to the center of thebeam, slightly above the beam waist, as describedin the text. The force applied on the object dependslinearly on its displacement from the trap center

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Trapping a particle with light

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Optical Tweezersrolf

WORKING OF TWEEZER

YouTube - Protein crystal in optical tweezers.flv

The Nd:YAG laser (1064 nm wavelength) is themost common laser choice because biological specimensare most transparent to laser wavelengthsaround 1000 nm. This assures as low an absorptioncoefficient as possible, minimizing damage tothe specimen, sometimes referred to as opticution.Perhaps the most important consideration in opticaltweezer design is the choice of the objective.

WORKING

Basic Components

Objective LensL2 L3L1

f1 + f2 f3 16 cm

Image created from Physlet at http://webphysics.davidson.edu/Course_Material/Py230L/optics/lenses.htm Physlet by Dr. Wolfgang Christian and Mike Lee

Laser

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Schematic diagramLaser

Beam expander

White Light Source

Cell

CCDCCD

Tip

ObjectiveColor Filter

Laser line mirror

Laser line mirror

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Dual beam tweezer design

Kinesin motor motion

RAY OPTICS RADIATION PATTERN•A laser beam is expanded and collimated. This collimated beam is directed through a microscope objective into a flow cell. Spheres with a higher index of refraction than the medium in the cell (water) will be trapped at the focus of the beam.

YouTube - real-life Tetris under a microscope.flv

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APPLICATIONSWe will calibrate the strength of an optical

trap (Optical Tweezer)

Optical Tweezers may be used to measure very small forces (femtoNewton, 10-15N)

Applications include Biophysics

THANk YOU FOR YOUR ATTENTION