An Introductory Information about Optical Tweezers Mustafa Yorulmaz Koç University, Material Science and Engineering

February 20, 2008 Koç University, Material Science and Engineering 2 Outline History of optical tweezers Basics of optical tweezers Physics beyond optical trapping Types of optical tweezers Possible uses and research areas A typical setup of optical tweezers Illustrative examples from our laboratory

February 20, 2008 Koç University, Material Science and Engineering 3 History of Optical Tweezers The technique of trapping was first applied in 1984 at Bell Laboratories In 1986, they showed a demo of optical tweezers They showed the damage- free manipulation on cells using an infrared laser in Optical Tweezers: A. Ashkin (*) (*)

February 20, 2008 Koç University, Material Science and Engineering 4 Basics of Optical Tweezers Optical Tweezers are examples of optical trapping which is a subfield of laser physics. They are used to trap and manipulate particles (in range from  m to nm) and also to measure the forces (in range from 1 to 100 pN) on these particles A strongly focused laser beam is used for trapping the particles. The particles that are of interest has to show dielectric property. *

February 20, 2008 Koç University, Material Science and Engineering 5 Physics Beyond Optical Trapping Trapping occurs due to radiation pressure of laser which results by the momentum change of light. There are two forces that let the particle to be hold in trap:  Scattering force: due to reflection of light (to push object)  Gradient force: due to refraction of light (to pull object) n particle >n medium so that F gradient >F scattering Using high NA objectives and high power lasers maximizes the trapping force. Schematic diagram showing the force on a dielectric sphere due to both reflection and refraction of two rays of light.

February 20, 2008 Koç University, Material Science and Engineering 6 Types of Optical Tweezers Single beam optical tweezers Holographic Optical Tweezers Experimental setup for our aerosol holographic tweezers ezers/Research/aerosols_HOT.htm Dual beam optical tweezers

February 20, 2008 Koç University, Material Science and Engineering 7 Possible uses and research areas By using optical tweezers, it is possible to  study and manipulate particles like atoms, molecules and small dielectric spheres (in range from  m to nm).  make force measurements of biological objects in piconewton range. Dielectric objects are attracted to the center of the beam, slightly above the beam waist, as described in the text. The force applied on the object depends linearly on its displacement from the trap center just as with a simple spring system. Optical tweezer for force measurements In the lasest research; this technique has been used for  biological investigations involving cells  cutting and ablating biological objects (cell fusion and DNA cutting)  force measurements of cell structures and DNA coiling  elasticity measurements of DNA So, optical tweezers has opened up several important new areas of study in biophysics

February 20, 2008 Koç University, Material Science and Engineering 8 A Typical Setup of Optical Tweezers CCD Collimation f1f2 M1 M2 M3 M4 f5O1 Telesentric f4f3 Computer Microscope Illumination Nd: YAG Laser (1064nm)

February 20, 2008 Koç University, Material Science and Engineering 9 Illustrative Examples From Our Laboratory: Manipulation of Microspheres Thanks to Ahmet Faruk Coşkun

February 20, 2008 Koç University, Material Science and Engineering 10 Illustrative Examples From Our Laboratory: Manipulation of Vibrio Cholerae Thanks to Ahmet Faruk Coşkun

February 20, 2008 Koç University, Material Science and Engineering 11 Thanks.. Questions?