Development of Next-Generation Optical Tweezers : The New Swiss Army Knife of Biophysical and Biomechanical Research

Abstract: In a time when microorganisms are controlling the world, research in biology is more relevant than ever and this requires some powerful instruments. Optical tweezers use a focused laser beam to manipulate and probe objects on the nano- and microscale. This allows for the exploration of a miniature world at the border between biology, chemistry and physics. New methods for biophysical and physicochemical measurements are continuously being developed and at Umeå University there is a need for a new system that combines several of these methods. This would truly be the new Swiss army knife of biophysical and biomechanical research, extending their reach in the world of optical tweezing. My ambition with this project is to design and construct a robust system that incorporates optical trapping with high-precision force measurements and Raman spectroscopy, as well as introducing the possibility of generating multiple traps by using a spatial light modulator (SLM). The proposed design incorporates four different lasers and a novel combination of signal detection techniques. To allow for precise control of the systems components and laser beams, I designed and constructed motorized opto-mechanical components. These are controlled by an in-house developed software that handles data processing and signal analysis, while also providing a user interface for the system. The components include, motorized beam blockers and optical attenuators, which were developed using commonly available 3D printing techniques and electronic controllers. By designing the system from scratch, I could eliminate the known weaknesses of conventional systems and allow for a modular design where components can be added easily. The system is divided into two parts, a laser breadboard and a main breadboard. The former contains all the equipment needed to generate and control the laser beams, which are then coupled through optical fibers to the latter. This contains the components needed to move the optical trap inside the sample chamber, while performing measurements and providing user feedback. Construction and testing was done for one sub-system at a time, while the lack of time required a postponement for the implementation of Raman and SLM. The system performance was verified through Allan variance stability tests and the results were compared with other optical tweezers setups. The results show that the system follows the thermal limit for averaging times (τ) up to ~1 s when disturbances had been eliminated, which is similar to other systems. However, we could also show a decrease in variance all the way to τ = 2000 s, which is exceptionally good and not found in conventional systems. The force-resolution was determined to be on the order of femtonewtons, which is also exceptionally good. Thus, I conclude that this optical tweezers setup could lie as a solid foundation for future development and research in biological science at Umeå University for years to come.