Nanopore detection of DNA molecules in magnesium chloride solutions

High translocation speed of a DNA strand through a nanopore is a major bottleneck for nanopore detection of DNA molecules. Here, we choose MgCl2 electrolyte as salt solution to control DNA mobility. Experimental results demonstrate that the duration time for straight state translocation events in 1 M MgCl2 solution is about 1.3 ms which is about three times longer than that for the same DNA in 1 M KCl solution. This is because Mg(2+) ions can effectively reduce the surface charge density of the negative DNA strands and then lead to the decrease of the DNA electrophoretic speed. It is also found that the Mg(2+) ions can induce the DNA molecules binding together and reduce the probability of straight DNA translocation events. The nanopore with small diameter can break off the bound DNA strands and increase the occurrence probability of straight DNA translocation events.