High-precision torque measurements with magneto-optical twezeers
When I first stepped in a research lab to do work for my master thesis,
I was deeply fascinated by the possibility of manipulating individual molecules
of DNA and I was very interested in using them as platforms
for mechanical and biochemical studies. I thus decided to implement a
methodology to apply and measure torsions on micro-systems, including single
DNA molecules. In particular, I used an integrated design of optical and
magnetic tweezers to perform direct torque measurements, achieving for the
first time a sensitivity of 1pNnm that, in turn, permitted
me to observe and measure the torque exerted by the laser light on the trapped
object and to identify and quantify different mechanisms contributing to the
transfer of angular momentum in optical tweezers experiments such as spin absorption, windmill, and non-linear magneto-optic effects.
Related publications
Capitanio M., Normanno D., and Pavone F.S., “High precision measurements of light-induced torque on absorbing micro-spheres”. Optics Letters 29, 19, 2231-2233 (2004)
Normanno D., Capitanio M., and Pavone F.S., “Spin absorption, windmill and magneto-optic effects in optical angular momentum transfer”. Physical Review A 70, 5, 053829(8) (2004) Capitanio M., Vanzi F., Broggio C., Cicchi R., Normanno D., Sacconi L., and Pavone F.S., “Exploring molecular motors and switches at the single-molecule level”. Microscopy Research and Technique 65, 194-204 (2004) People involved
Prof. Francesco S. Pavone
Dr. Marco Capitanio Institutions & fundings
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Magneto-optical tweezers used to trap and rotate super-paramagnetic micro-spheres
Rotation detection by DIC microscopy and micro-manipulator calibration against the drag torque 
Direct measure of the light-induced torque 
Separation and quantification of the different contributions to the transfer of optical angular momentum 
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