title: Optical trapping of coated microspheres.
abstract: In an optical trap, micron-sized dielectric particles are held by a tightly focused laser beam. The optical force on the particle is composed of an attractive gradient force and a destabilizing scattering force. We hypothesized that using anti-reflection-coated microspheres would reduce scattering and lead to stronger trapping. We found that homogeneous silica and polystyrene microspheres had a sharp maximum trap stiffness at a diameter of around 800 nm--the trapping laser wavelength in water--and that a silica coating on a polystyrene microsphere was a substantial improvement for larger diameters. In addition, we noticed that homogeneous spheres of a correct size demonstrated anti-reflective properties. Our results quantitatively agreed with Mie scattering calculations and serve as a proof of principle. We used a DNA stretching experiment to confirm the large linear range in detection and force of the coated microspheres and performed a high-force motor protein assay. These measurements show that the surfaces of the coated microspheres are compatible with biophysical assays.
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Bormuth
authors.forename: Anita
authors.initials: A
authors.lastname: Jannasch
authors.forename: Marcel
authors.initials: M
authors.lastname: Ander
authors.forename: Carlos M
authors.initials: CM
authors.lastname: van Kats
authors.forename: Alfons
authors.initials: A
authors.lastname: van Blaaderen
authors.forename: Jonathon
authors.initials: J
authors.lastname: Howard
authors.forename: Erik
authors.initials: E
authors.lastname: Schäffer
mesh_terms: D020099:Coated Materials, Biocompatible / Q000737:chemistry* / Q000528:radiation effects; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure*; D008863:Microspheres; D052898:Optical Tweezers; D012822:Silicon Dioxide / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D020099:Coated Materials, Biocompatible; D012822:Silicon Dioxide; D004247:DNA