Here we have two more recent articles talking about our mehod to measure optical forces:
Derek Craig, Alison McDonald, Michael Mazilu, Helen Rendall, Frank Gunn-Moore, and Kishan Dholakia. “ Enhanced Optical Manipulation of Cells Using Antireflection Coated Microparticles”.ACS Photonics, 2 (10), pp 1403–1409, (2015)
“In molecular studies, an optically trapped bead may be functionalized to attach to a specific molecule, whereas in cell studies, direct manipulation with the optical field is usually employed. Using this approach, several methods may be used to measure forces with an optical trap. However, each has its limitations and requires an accurate knowledge of the sample parameters. In particular, force measurements can be challenging when working with nonspherical particles or in environments with an inhomogeneous viscosity, such as inside the cell. Recent developments in the field are moving toward obtaining direct force measurements by detecting light momentum changes. For this approach, the calibration factor only comes from the detection instrumentation and negates the requirement to recalibrate for changes in experimental conditions”.
- Xing Ma, Anita Jannasch, Urban-Raphael Albrecht, Kersten Hahn, Albert Miguel-López, Erik Schäffer, and Samuel Sánchez. “Enzyme-Powered Hollow Mesoporous Janus Nanomotors”. Nano Lett., 15 (10), pp 7043–7050, (2015).
“Using optical tweezers, we directly measured a holding force of 64 ± 16 fN, which was necessary to counteract the effective self-propulsion force generated by a single nanomotor. The successful demonstration of biocompatible enzyme-powered active nanomotors using biologically benign fuels has a great potential for future biomedical applications.”