CONSTRUCTION OF A RAMAN TWEEZER SYSTEM

FOR INVESTIGATION OF BIOLOGICAL MOLECULES

Günay Başar

İstanbul Teknik Üniversitesibasar@itu.edu.tr

International Symposium on Molecular Spectroscopy 62nd Meeting - June 18-22, 2007

• Basic principles of optical tweezers• Experimental set-up• Advantages of Raman Tweezer set-up• Test measurements on micro particles

and living cells

Outline

Basic Principles of Optical Tweezers

Light besides energy carries

Lineer momentum Force Classical : EM theory, Radiation pressure

Quantum : Photon momentum,

Angular momentum Torque

dP Fdt

hpc

dLdt

Radiation Presure→ Optical Trapping

1 mW

1μm F ~10 pNm ~pg

F ~ 10 pN

a ~105 g

a b

Fb Fa

F

b a

a b

b a

a b

FFa Fb

f

f

fFa

Fb

F

b

a

La se r Be a m

M ic . O b je c tive

PinP o ut

(A. Ashkin, Biophys. J. (61), 1992)

21

2

21

2

cos(2 2 ) cos 21 cos 2

1 2 cos 2

sin(2 2 ) sin 2sin 2

1 2 cos 2

z scat

y grad

T r Rn PF F Rc R R r

T r Rn PF F Rc R R r

Single Ray SolutionP : PowerMomentum per unit time:

1n Pc

P

r

O

y

zPT2

PTR2

PTR2 2

PRn1

n2

Be a m

f

r

m a x

S

rm a x

x

y

z z

y

w

O

Be a mr rm a x

w

z

f

Be a m a xis

n̂

Fg S

Fs

O

M ic .o b je c tiveb a c k a p e rture

Extended Laser Beam

• Large NA objectives• Overfilling• n2 > n1 • Power ~1mW is enough to trap

Critical Points for Optical Trapping

Experimental setup

1µm trapped polystyrene particle

4.6 µm trapped polystyrene particle

~ 5 µm trapped yeast cell

~ 5 µm trapped yeast cell

• The ability to get Raman Spectrum of a single living object in their natural environment.

• Decreasing of background signals from cover slip.

• No mechanical immobilization of living cells.

Advantages of Raman Tweezer Set-up

Excitation wavelength: 780 nmPower: 6 mW on the sampleAccumulation: 100 s

Raman spectrum of trapped polystyrene particle

Raman spectrum of trapped yeast cell

C. Xie et al. Opt. Exp. 25, 6208-6214 2004

Collaboration

Istanbul University

Physics Department

Prof.Dr. Sevim Akyuz

• Optimizing Laser Tweezer Raman Spectrometer• Investigation of interaction between cell membranes and their environment

Future Work

Support by the Scientific and Technological Research Council of Turkey under the project number 105T482 is gratefully acknowledged.

Our Laser Spectroscopy Groupat Istanbul Technical UniversityPhysics Engineering Department

PhD studentSeda Kin

MsC studentUğur Parlatan

BsC studentsOnur PusulukBerkin Malkoç

Group leaderAssoc.Prof. Dr. Gunay Basar

Thank You!