Tribological Properties Between The Dna-Modified Afm Probe And Several Nanoporn Materials

In the Third Technological Revolution, genetic engineering is one of the most important achievements. Gene sequencing technology is the basis of genetic engineering. How to realize the precise, fast and low-cost gene sequencing has always been a hot research area. Nanopore sequencing technology is a way to detect basic group through detecting the blocking current when the DNA passes through nanopore by electrophoresis. It is considered to be able to cost less than $1,000 and 24 hours by the novel gene sequencing method. Nowadays, one of the main remaining challenges is to slow down the DNA translocation speed through a nanopore. When a DNA molecule translocated an a-hemolysin pore, the typical rate was about 1-20 μs per base. Such speed was two orders faster for the accurate measurement of the block ionic current over the background noise. Increasing the friction between DNA and nanopore is a simple method to reduce translocation speed. Both nanoporous materials and salt concentration of solution may affect the friction between the DNA and the nanopore. Therefore, it is very important to investigate the effect of nanoporous material and salt concentration of solution on the friction behaviors of DNA.In this paper, the atomic force microscope (AFM) silica probes were used, which have a diameter of 2 μm. After pre-treatment by 3-triethoxysilyl-l-Propanamine (APS) solution, the DNA chains can be easily adsorbed on the surfaces of AFM probes. By using the DNA-modified AFM probes, the friction behavior of several nanopore materials, such as SiO2, Si3N4 and APS-SiO2, was investigated. The effect of salt concentration of solution (0.001 mol/L,0.01 mol/L,0.1 mol/L) on the friction property was also studied. The main conclusion can be summarized as follows:1. After pre-treatment by 3-triethoxysilyl-l-Propanamine (APS) solution, the DNA chains can be easily adsorbed on the surfaces of silica AFM probes. By measuring the force-displacement curve between probe and the mica substrate, it was found that the DNA molecule can firmly adsorb on the probe surface. Thereby, a method was proposed to measure the friction between DNA and nanopore material.2. In aqueous environments, the friction between the DNA-modified probes and three nanopore materials was investigated. The variation of friction force followed the following turn:SiO2<Si3N4<APS-SiO2. It was suggested that both nanopore surface roughness and surface charge characteristics would affect the friction. When the roughness of nanopore surface is close, it can effectively increase the friction by reducing electrostatic repulsion between DNA and material surface or using a positively charged surface material.3. The effect of salt concentration of solution on the friction property was also studied. With the increase of salt concentration from 0.001 mol/L to 0.1 mol/L, the concentration of Na+ can partly neutralize negatively charged phosphate groups on the DNA backbone. DNA films are more flexible and the friction between the DNA and the substrate is smaller. Low salt concentration can increase the friction between DNA and nanopore material, and therefore more conducive to nanopore sequencing technology.