Identification of four single-stranded DNA homopolymers with a solid-state nanopore in alkaline CsCl solution

DNA sequencing via solid-state nanopores is a promising technique with the potential to surpass the performance of conventional sequencers. However, the identification of all four nucleotide homopolymers with a typical SiN nanopore is yet to be clearly demonstrated because a guanine homopolymer rapidly forms a G-quadruplex in a typical KCl aqueous solution. To address this issue, we introduced an alkaline CsCl aqueous solution, which denatures the G-quadruplex into a single-stranded structure by disrupting the hydrogen-bonding network between the guanines and preventing the binding of the K+ ion to G-quartets. Using this alkaline CsCl solution, we provided a proof-of-principle that single-stranded DNA homopolymers of all four nucleotides could be statistically identified according to their blockade currents with the same single nanopore. We also confirmed that a triblock DNA copolymer of three nucleotides exhibited a trimodal Gaussian distribution whose peaks correspond to those of the DNA homopolymers. Our findings contribute to the development of practical DNA sequencing with a solid-state nanopore.