Research On The Transport Of Molecules With Different Surface Charge Densities In A Confined Channel

Biomolecules,such as DNA,protein and so on,controls the indicidual characteristics and life phenomenon.Therefore,it is significative to master the biological information contained in the biomolecules(DNA,protein and so on).Nanopore is a kind of powerful tool to detect single molecules and investigate fundamental biological processes based on its high throughput and sensitivity.In this thesis,the solid-state nanopores are used to research molecules(DNA and streptavidin(SA))with different charge densities transporting through nanopores.The main research work and results are as follows:1)Exploring the force of DNA and SA in the electrolyte solution at nanoscale.According to experimental results,the behaviors of DNA and SA transport through a solid-state nanopore are dominated by electrophoresis(EP)and electroosmotic flow(EOF),respectively.2)The effects of DNA concentration on capture rate and translocation configuration with different sized nanopores and applied voltages were studied.Three classes of DNA translocation configuration had been observed including linear translocation,folded translocation,and co-translocation.In the case of relatively large sized nanopore or high applied voltage,considerable co-translocation events had been detected.The percentage of co-translocation events also increases with DNA concentration,which leads to the relationship between capture rate and DNA concentration deviates from linearity.Therefore,in order to reflect the number of translocation molecules accurately,the capture rate should be corrected by double-counting co-translocation events.In addition,experimental results exhibit monotonically increasing capture rate versus applied voltage for small sized pore.However,for large sized nanopore,the concentration of DNA influences the dependence of the percentage of linear translocation events on applied was found.3)Exploring the effects of nanopore size,applied voltage and electrolyte solution concentration on the duration and capture rate of SA molecules.Experimental results show the frequency of translocation events detected by the nanopore with a diameter slightly larger than length is ≈17 times larger than that in previously reported work.However,as pore diameter increases,the maximum detectable velocity of SAs decreases.Moreover,it was found the SA translocation frequency slowly increases with the amplitude of voltages,and then declines at a threshold bias.Furthermore,it was also found that frequency of SAs translocation events declines and duration saturates at high salt concentration.4)Numerical simulations elucidate the enhanced frequency comes from a concave-shape EOF in the nanopore,which provides a low velocity region allowing for numbers of SAs moving slowly enough to be detected.However,as pore diameter increases,the maximum detectable velocity of SAs decreases due to the reduced signal-to-noise ratio.The bandwidth limitation combined with the non-linear dependence of EOF velocity in the pore central region on applied voltage leads to SA translocation frequency declines at a threshold bias.Moreover,it was found that electrophoresis dominant area in the nanopore decreases and staturates at high salt concentration.