Departmental Papers (CBE)

Document Type

Journal Article

Date of this Version

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.


Postprint version. Published in Review of Scientific Instruments, Volume 77, Issue 11, Article 113702, November 2006, 10 pages.
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Date Posted: 01 December 2006

This document has been peer reviewed.