Line Optical Tweezers Instrument for Measuring Nanoscale Interactions and Kinetics

We describe an optical tweezers instrument for measuring short-ranged colloidal interactions, based on a combination of a continuous wave line optical tweezers, high speed video microscopy, and laser illumination. Our implementation can measure the separation of two nearly contacting microspheres to better than 4 nm at rates in excess of 10 kHz. A simple image analysis algorithm allows us to sensibly remove effects from diffraction blurring and microsphere image overlap for separations ranging from contact to at least 100 nm. The result is a versatile instrument for measuring steric, chemical and single-molecular interactions and dynamics, with a force resolution significantly better than achievable with current atomic force microscopy. We demonstrate the effectiveness of the instrument with measurements of the pair interactions and dynamics of microspheres in the presence of transient molecular bridges of DNA or surfactant micelles. Comments Postprint version. Published in Review of Scientific Instruments, Volume 77, Issue 11, Article 113702, November 2006, 10 pages. Publisher URL: http://dx.doi.org/10.1063/1.2387893 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/cbe_papers/78 Line optical tweezers instrument for measuring nanoscale interactions and kinetics Paul L. Biancaniello Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104 John C. Crocker Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Received 23 June 2006; accepted 9 October 2006; published online 15 November 2006 We describe an optical tweezers instrument for measuring short-ranged colloidal interactions, based on a combination of a continuous wave line optical tweezers, high speed video microscopy, and laser illumination. Our implementation can measure the separation of two nearly contacting microspheres to better than 4 nm at rates in excess of 10 kHz. A simple image analysis algorithm allows us to sensibly remove effects from diffraction blurring and microsphere image overlap for separations ranging from contact to at least 100 nm. The result is a versatile instrument for measuring steric, chemical and single-molecular interactions and dynamics, with a force resolution significantly better than achievable with current atomic force microscopy. We demonstrate the effectiveness of the instrument with measurements of the pair interactions and dynamics of microspheres in the presence of transient molecular bridges of DNA or surfactant micelles. © 2006 American Institute of Physics. DOI: 10.1063/1.2387893