Photonic Tweezers for Optical Manipulation of Cells and Tissues
Optical tweezers represent a powerful tool for studying forces in biological samples. In this thesis, I explored applications of optical tweezers that pushed the technique beyond its limitations. In fact I worked on extending the range of forces applicable by the tweezers and on applying optical tweezers for the study of cell-cell junctions in tissues. Typical values for optical tweezers forces range between tenths to hundreds of pN, with only few examples of tweezers reaching nN forces. I synthesised photonically structured probes and obtained tweezers capable of nN forces. Furthermore, I optimised the probes to make them more suitable for biological experiments, I investigated alternative synthesis methods and conducted proof-of-concept studies for their application in cellular biology. Regarding the application of tweezers in tissues, I demonstrated their use for the study of tension in developing chick embryos. At about 6h from the egg’s deposition, the chick embryo initiates gastrulation: the embryo rearranges from a single layered structure into a multi-layered one. The process is regulated by the large-scale highly coordinated flows of the cells in the epiblast. There are evidences that contraction and preferential cells intercalation in the posterior area of the embryo drive the process. The contraction in the posterior area seems to be correlated with the presence of myosin II cables. I optically manipulated cell-cell junctions in chick embryos while recording their deformation. I measured the difference response of junctions studied under different conditions. The results support the idea that junctions in the posterior area of embryos starting gastrulation (5h old) are under stronger tensions than junctions in younger embryo and junctions in the anterior area of the organism. Moreover, when embryos are treated with myosin I or myosin II inhibitors, tension in the junctions is reduced.
physics, Optical tweezers, Optical trapping, optical manipulation, Chick embryo, Dictyostelium Discoideum, antireflection coating
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