Research On DNA Motion Control Technology Based On Solid-State Nanopore

Solid-state nanopore single-molecule technology is the most promising method for low-cost and fast reading of DNA sequences,which is the core of the third-generation gene sequencing technology.The main problem with controlling the motion of DNA through solid-state nanopore is that the low spatial resolution of solid-state nanopores and the fast speed of DNA passing through solid-state nanopore.To solve these problems,the key techniques for controlling the motion of DNA through solid-state nanopore are studied from the aspects of finite element simulation and experiment in this paper.The main research methods and work results of this paper are as follows:(1)The solid-state nanopore DNA experiment was simulated by multi-physical coupling simulation software COMSOL Multiphysics.The simulation results show that reducing the thickness of silicon nitride membrane,reducing the concentration of buffer and increasing the negative surface charge density of solid-state nanoporous membrane can reduce the critical voltage at which DNA is captured by solid-state nanopores.The conductivity of the solid-state nanopore increases with the increase of the buffer concentration,and the I-V curve of the nanopore drifts away from the zero point due to the strong surface conductance effect when the buffer concentration is too low.Increasing the buffer concentration and decreasing the bias voltage can reduce the speed that DNA passes through the nanopore,but it also reduces the amplitude of the blocking current.(2)Based on the results of solid-state nanopore model simulation,the fabricaion process of solid-state silicon nitride nanopores is optimized.Solid-state nanopores with small pore size and excellent performances are fabricated by thinning silicon nitride membrane before drilling with FIB,which laid a solid foundation for the experiment.The translocation experiments of DNA through solid-state nanopore are carried out under different concentrations,different bias voltages and different buffers to study the behavioral characteristics of DNA translocation.The results show that in the range of 0.1-1 mol/L,as the buffer concentration increases,the blocking current amplitude increases,and the DNA translocation speed decreases.As the bias voltage increases,the blocking current amplitude increases,and the DNA translocation speed increases.The stronger the binding of the positive valence ion to the DNA in the buffer,the lower the DNA translocation speed that the DNA through the solid-state nanopore.(3)The method of the streptavidin-modified magnetic beads binding biotin-modified DNA is explored.The characteristics of ion current signal when magnetic bead bound DNA,pure magnetic beads and streptavidin interact with solid-state nanopores are analyzed,which is beneficial to the identification of experimental phenomena.The experiments of bead-bound DNA through solid-state nanopore are carried out at different bias voltages.The experimental results show that the DNA is subjected to the electric field force of the bias voltage and the viscous resistance of the buffer when it through the solid-state nanopore.The magnetic beads bound DNA can increase the viscous resistance of the DNA and greatly reduce the translocation speed.When the bias voltage is lower than 300 mV,the translocation speed of the bead-bound DNA is decreases as the bias voltage decreases.(4)Design and build an experimental platform for the magnetic tweezers control system,including the material selection design of the magnetic tweezers,the finite element simulation of the magnetic field distribution and the speed control of the nano-displacement platform.The magnetic tweezers system controls the magnetic bead-bound DNA through solid-state nanopore experiments,which proves that the magnetic tweezers control system can provide a large enough,stable and controllable magnetic field to control the translocation speed of DNA through the solid nanopore.