Theory,Experiment And Single Molecule Application Of Novel Modulated Optical Tweezers

This thesis starts with the current status and situation of optical tweezers, reviews novel techniques combined with optical tweezers and discusses novel problems that people haven’t solved in related application area. The main focus of thesis are theory, experiment and application of novel modulated optical tweezers which covers time-sharing optical tweezers and holographic optical tweezers. On the theory of optical trapping, we utilize Monte Carlo technique to simulate the relationship between effective stiffness and trap switching frequency; On holographic optical tweezers, we employ Fourier optics to calculate the hologram for array tweezers, further study the dynamics of cells under vortex tweezers, parallel calibrate array tweezers with high performance computer and manipulate nanoplatelets holographic optical tweezers; On single molecule biophysics, we constructed state-of-art high resolution dual trap optical tweezers with single molecule detection and systematically studied the DNA hairpin dynamics with different oligonucleotide inhibitors.Single molecule biophysics is a highly interdisciplinary subject, involving mechanics, electronics, optics, computer science and biochemistry. Typical approaches to study single molecules are atomic force microscope, optical tweezers, magnetic tweezers, single molecule fluorescence localization and single molecule fluorescence detection. For optical tweezers, since its invention in1986, it becomes an important research tool in colloidal science, soft matter and single molecule biophysics. Optical tweezers technique itself has developed with those new requirements, absorbing many new techniques. Time-sharing and spatial light modulation are two commonly utilized methods among those novel techniques.This thesis mainly discusses some topics on holographic optical tweezers based on spatial modulation, time-sharing optical tweezers and their related applications in single molecule biophysics. The holograms were calculated through Fourier optics, and the effective stiffness of time-sharing optical tweezers was studied with Monte Carlo technique. Holographic optical tweezers was utilized to capture and rotate cells, to parallel manipulate nanoplatelets.On the theory of holographic optical tweezers, we summarize related theories of holographic optical tweezers and utilize the adaptive-additive algorithm to calculate the holograms, and our algorithm is verified in the holographic optical tweezers experiments. On the experimental part, we successfully capture and arrange multiple microscopic particles with array tweezers and rotate single or multiple cells with vortex tweezers; we studied the dynamics of yeast cell in vortex tweezers in more detail; we designed, fabricated, characterized ZrP nanoplatelets and use the holographic optical tweezers to manipulate and arrange them; we design hybrid system based on holographic tweezers and high resolution tweezers for measurement of soft matter.On the theoretical part of time-sharing optical tweezers, we utilize Monte Carlo technique to simulate the Brownian motion of microsphere in time-sharing optical tweezers and further calculate the effective trap stiffness. Simulation results demonstrate that the effective stiffness grows exponentially with the trap switching frequency and saturates at higher frequencies. We employ rotating glass plate and acousto-optic deflector to form time sharing optical tweezers and the experimental results confirmed the simulation both in the low frequency range and in a broad frequency range.On the application of time-sharing optical tweezers, we combined time-sharing optical tweezers with single molecule fluorescence detection, successfully achieved lbp resolution based on the time-sharing high resolution dual trap optical tweezers. This hybrid tweezers machine can work on different modules, including constant force mode, variable force mode, single molecule fluorescence detection, wide field fluorescent imaging. We designed and synthesized a series of DNA oligunucleotides with different length, different sequence, different position as inhibitor and studied the dynamics change of DNA hairpin induced by the inhibitor. We successfully imaged single λDNA molecule with wide field fluorescent microscopy.Novel modulation optical tweezers is a broad research area, involving the design and construction of optical tweezers and the deepened application of this technique. In colloidal and soft matter sciences, holographic optical tweezers based on liquid crystal spatial light modulator with the ability to parallel manipulate nanoparticle will potentially be employed to study the colloidal assembly, multiple particle interaction. The study of force and extension change in microscopic and nanoscopic level helps people understand the dynamics of macromolecules such as protein/RNA/DNA or their complex structure. These information is not obtainable and complementary in traditional approaches based on bulk experiment. High resolution optical tweezers combined with single molecule detection are able to measure the conformational changes and visualize the macromolecule simultaneously.The novel modulation tweezers in this thesis includes time sharing optical tweezers with time multiplexing and holographic optical tweezers with liquid crystal spatial light modulator. Time sharing optical tweezers will be introduced in Chapter4with single molecule application in Chapter5; Chapter2and3will introduce the theoretical, experimental and application part of holographic optical tweezers utilizing liquid crystal spatial light modulator; prior to the development of holographic optical tweezers, we fabricated pure phase hologram with ion etching technique and shaped the laser beam into superimposed Laguerre-Gaussian beam which can be found in Chapter6; Chapter7demonstrates another spatial light modulation technique to shape the laser beam with amplitude type modulator, digital micromirror device; Chapter8summarizes the whole project during my PhD thesis and prospectively overview the future work of holographic optical tweezers in our lab.