Quantitatively Measuring the Interactions between Bridging Cells using Optical Tweezers

The development and function of multicellular organisms deeply rely on cell-cell interactions. Therefore, the ability of artificially build up cell junctions and bridging different types of cells in vitro is badly demanded for biological research. Herein, four click reagents Mal-CBT, Mal-Cys, Mal-Alkyne, and Mal-N3 are firstly introduced to bridge cells of three colors. Then, the bridging probability between Mal-Cys-modified and Mal-CBT-modified HEK 293 cells are quantitatively measured by optical tweezers as well. The experiment clearly showed that the efficiency of cell bridging was dramatically improved from 19.15% to 66.10% by CBT-Cys click reaction. After that, image analysis techniques were employed via Matlab in order to tracking image sequences obtained during stretching process. By these means, the force-time curve was constructed and rupture force of bridged cell pairs was obtained to be 153.8 pN at a force-loading rate of 49 pN s-1. This rupture force was of the same order of magnitude as the previously reported simulated result for a covalent bond[1]. The same method can also be applied in rupture force measurement of other covalent bonds at low force-loading rate.[1] S.W. Schmidt, M.K. Beyer, H. Clausen-Schaumann, Dynamic strength of the silicon-carbon bond observed over three decades of force-loading rates, J. Am. Chem. Soc., 2008, 130, 3664-3668.