Fabrication of 3D micro-objects by two-photon lithography for optical tweezers manipulation

In the last decade Optical Tweezers (OT) and Two Photon Polymerization (TPP), two already established techniques for contactless manipulation of micro-objects in liquids and for the fabrication of three-dimensional micro-objects of arbitrary shape, respectively, have consolidated their presence in the laboratory practice, not only as subject of scientific and technical investigations, but also as convenient tools for applications to other fields. This thesis tries to combines these worlds, using TPP to fabricate micro-objects that could be trapped and actuated by OT, with the aim of pushing forward the possibilities of producing new tools, in particular for cell biology studies. We demonstrated here a convenient scheme for the fabrication of 3D micro-objects by two-photon lithography, their release from the substrate under physiological conditions and actuation by optical tweezers. This opens interesting possibilities in mechanobiology experiments, for fabricating and precisely placing 3D micro-tools in proximity with living cells and actuating them by optical tweezers (OT) to operate on cells. These possibilities can be extended to the simultaneous dynamical manipulation of more trapped objects as demonstrated in recent years. In the present work micro-objects with and without mirror-symmetry were fabricated by two photon lithography (TPL) in SU-8 negative photoresist on a water soluble sacrificial layer on glass, released from the substrate in water, and set into rotational motion by optical tweezers, exploiting the optically induced torque generated by a focused laser beam interacting with micro-objects with broken mirror-symmetry. While fabricated simple micro-cones were found stable in the optical trap, micro-cones modified with the addition of chiral features were propelled away due to the imbalance of scattering, gradient optical forces and fluid dynamic forces generated in the rotation. In the near future the combination of optical tweezers, two-photon polymerization and advanced imaging techniques will enable new studies of the effects of mechanical stimulation of a cell onto the molecular events inside the cell.