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Biophys. J. BioFAST: First Published May 27, 2005. doi:10.1529/biophysj.104.054536
© 2005 by the Biophysical Society.

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SPECTROSCOPY, IMAGING, OTHER TECHNIQUES

Temperature Control Methods in a Laser-Tweezers System

Hanbin Mao 1, J. Ricardo Arias-Gonzalez 1, Steven B. Smith 2, Ignacio Tinoco, Jr. 3 and Carlos Bustamante 2*

1 Lawrence Berkeley National Lab
2 University of California, Berkeley
3 Univ. of California - Berkeley

* To whom correspondence should be addressed. E-mail: carlos{at}alice.berkeley.edu.

Submitted on October 29, 2004
Revised on January 29, 2005
Accepted on 9 May 2005


  Abstract
Two methods of temperature control of a dual-beam optical-tweezers system are compared. In the first method, we used a 975 nm infrared laser to raise a temperature of 5.6°C/100mW in a non-heating (830 nm) optical trap. The temperature increment logarithmically decreases towards the periphery of the heating beam, causing a fluid convection of 8mm/s inside a 180 mm thick micro-chamber. In the second method, heating or cooling fluid was pumped through copper jackets that were placed on the two water immersion objectives on both sides of the microchamber to control its temperature from 4.5 °C to 68 °C. The temperature controlled by the second method was both stable and homogeneous, inducing little fluid convection that would disturb some single-molecule applications. An analysis of the power spectrum of the thermal force on a trapped bead showed no detectable vibration due to the liquid circulation. In both methods, force was measured directly by sensors of momentum-flux of light, independent of environmental disturbances including refractive index changes that vary with temperature. The utility of the second method was demonstrated in single-molecule experiments by measuring the mechanical stretch of a 41 kbp lambda double-stranded DNA at temperatures ranging from 8.4 °C to 45.6°C.

Key Words: circulator, heating laser, optical tweezers, single molecule




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Copyright © 2005 by the Biophysical Society.