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First published online May 20, 2008
doi: 10.1242/10.1242/jcs.030999

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Single-cell force spectroscopy

¹ Biotechnology Center, University of Technology Dresden, Germany
² Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
³ Center for Nanoscience and Applied Physics, Ludwig-Maximilians-University Munich, Germany

View larger version (10K): [in this window] [in a new window]   Fig. 1. Converting a cell into a probe. (A) The apex of a lectin-functionalized (often by binding concanavalin A) AFM cantilever is positioned above a cell. (B) The cantilever is gently pushed (generally with a force of <1 nN) for several seconds onto the cell. (C) The cantilever-bound cell is separated from the support and allowed to establish firm adhesion. (D) A phase-contrast image of a cell (arrow) bound to a tip-less cantilever.

View larger version (29K): [in this window] [in a new window]   Fig. 2. Single-cell force spectroscopy. Depiction of a cell-adhesion measurement (A) for which characteristic approach (green) and retraction (blue) traces are shown (B). (A) In this technique, the cell and the substrate are brought into contact (AI). The substrate that is probed can be another cell, a functionalized surface or an organic matrix. The position on a photodiode (PD) of a laser beam (red line) that is reflected off the back of the cantilever measures the deflection of the cantilever and thus the force that acts on the cantilever. During the approach (denoted by green arrows), the cell (probe) is pressed onto the substrate until a pre-set force (usually <1 nN) is reached (AII). After a contact time ranging from 0 to 20 minutes, the cell is retracted from the substrate (marked by blue arrows), and a force-distance curve is recorded (B). This curve corresponds to a cell-adhesion signature. As the strain on the cell increases, bonds that have been formed between the substrate and the cell break sequentially (AIII) until the cell has completely separated from the surface (AIV). The maximum downward force exerted on the cantilever of the atomic force microscope is referred to as the detachment force (Fdetach). During the separation of the cell from the surface, two types of molecular unbinding events can occur. In the first event, the receptor remains anchored in the cell cortex and unbinds as the force increases (denoted as jumps). The second type of unbinding event occurs when receptor anchoring is lost and membrane tethers are pulled out of the cell. In the unbinding-force–distance curve, long plateaus of constant force characterize tethers. The shaded area in B represents the measured work of cell detachment from the substrate. The lower-case letters (a, b and c) denote different phases of cell-substrate detachment (see text for details). Steps I-IV shown in A are also indicated in B.

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