title: Calibration of optical tweezers for in vivo force measurements: how do different approaches compare?
abstract: There is significant interest in quantifying force production inside cells, but since conditions in vivo are less well controlled than those in vitro, in vivo measurements are challenging. In particular, the in vivo environment may vary locally as far as its optical properties, and the organelles manipulated by the optical trap frequently vary in size and shape. Several methods have been proposed to overcome these difficulties. We evaluate the relative merits of these methods and directly compare two of them, a refractive index matching method, and a light-momentum-change method. Since in vivo forces are frequently relatively high (e.g., can exceed 15 pN for lipid droplets), a high-power laser is employed. We discover that this high-powered trap induces local temperature changes, and we develop an approach to compensate for uncertainties in the magnitude of applied force due to such temperature variations.
authors.affiliation: Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California.
authors.forename: Yonggun
authors.initials: Y
authors.lastname: Jun
authors.affiliation: Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California.
authors.forename: Suvranta K
authors.initials: SK
authors.lastname: Tripathy
authors.affiliation: Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California.
authors.forename: Babu R J
authors.initials: BR
authors.lastname: Narayanareddy
authors.affiliation: Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California.
authors.forename: Michelle K
authors.initials: MK
authors.lastname: Mattson-Hoss
authors.affiliation: Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California. Electronic address: sgross@uci.edu.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Gross
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002138:Calibration; D057809:HEK293 Cells; D006801:Humans; D006868:Hydrolysis; D016547:Kinesins / Q000378:metabolism; D055595:Mechanical Phenomena; D052898:Optical Tweezers; D013696:Temperature
chemical_list: D000255:Adenosine Triphosphate; D016547:Kinesins