The setup development has been one of the main activities of the grant, which is at the moment in the final stage of construction. The final setup design consists of a dual trap geometry, i.e a molecule is embedded between optically trapped beads, used to apply forces in the pN range and measure the corresponding molecular elongation. At the same time, a visible laser is focused at the apex of a metallic tip, which is used as nanometric Raman probe. A single objective (used for focusing the 3 beams) is fixed next to a fluidic cell (with the tip mounted steadily on it). The sample cell can be freely moved with nanometric precision (3D piezo stage) with respect to the objective, allowing the positioning of the tip apex at the exact focus of the Raman light. At the same time, the two optically trapped beads with a molecule embedded between them can be independently moved around the tip by changing the incidence angle of the OT beams into the objective using steering mirrors. Currently, all required elements are purchased and are being installed. The project long-term viability is ensured through a collaboration with the company supplying the optical twezeers as well as the investment of the host institution.
Moreover, we have worked on the investigation of supramolecular systems and their interactions by means of optical tweezers. We have studied the shuttling dynamics of rotaxane-based molecular shuttles as a function of salt concentration in the environment. We have found that increasing NaCl concentration, the coexistence force at which the macrocycle resides equally in both stations increases. This result implies that the hydrogen bonding between macrocycle and stations weakens at lower concentration of ions. Energy landscapes and kinetic rates are calculated for each salt concentration, showing the change in the energy barriers as a function of applied force. Moreover, we were able to observe in situ the change in dynamics upon increase/decrease of salt concentration, in an impressive live experiment. These results open the door to the systematic extension of OT to the field of supramolecular chemistry and a publication describing them is currently under preparation.
Finally, the fellow has been involved in several side-projects and collaborations, related with different aspects of the TweeTERS project. Within the enhanced-Raman spectroscopy field, we have participated in the spectroscopic characterization of nanomaterials (TMDCs, carbon-based materials and heterostructures of those). In the field of optical tweezers, we are currently working on a project where we use OT hoping results of a molecular shuttle to demonstrate experimentally the principle of microscopic reversibility, expanding the application of the technique to the fundamental understanding of chemical principles.
The project has been very productive scientifically, with 5 publications in high impact journals, and 4 additional ones in peer-review or preparation phases. Furthermore, it has been presented in 5 conferences.
