All-Optical Constant-Force Laser Tweezers

• Published in: Biophysical journal 2004-09, Vol.87 (3), p.1972-1980
• Main Authors: Nambiar, Rajalakshmi, Gajraj, Arivalagan, Meiners, Jens-Christian
• Format: Article
• Language: English
• Subjects: Biochemistry; Biophysical Phenomena; Biophysics; DNA - chemistry; DNA - ultrastructure; Lasers; Light; Micromanipulation - instrumentation; Micromanipulation - methods; Microscopy - methods; Microspheres; Models, Statistical; Molecular biology; Scattering, Radiation; Scientific apparatus & instruments; Spectroscopy, Imaging, Other Techniques; Stress, Mechanical; Time Factors
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.103.037697

Optical tweezers are a powerful tool for the study of single biomolecules. Many applications require that a molecule be held under constant tension while its extension is measured. We present two schemes based on scanning-line optical tweezers to accomplish this, providing all-optical alternatives to force-clamp traps that rely on electronic feedback to maintain constant-force conditions for the molecule. In these schemes, a laser beam is rapidly scanned along a line in the focal plane of the microscope objective, effectively creating an extended one-dimensional optical potential over distances of up to 8 μm. A position-independent lateral force acting on a trapped particle is created by either modulating the laser beam intensity during the scan or by using an asymmetric beam profile in the back focal plane of the microscope objective. With these techniques, forces of up to 2.69 pN have been applied over distances of up to 3.4 μm with residual spring constants of