Figure 4.

Detection of DNA homopolymer poly(dT) with protein and solid-state nanopores. (a) Example of a translocation event, illustrating the SNR. (b) Schematic comparing the relative sizes of MspA (green), α-HL (red), ReFraC (blue), MoS₂ (black), and solid-state SiN_x (purple). Adapted with permission from ref (2). Copyright 2015 IOP Publishing Ltd. (c) Example of translocation events of poly(dT) molecules through MspA¹⁴ channel (green), α-HL pore (red), ReFraC pore (blue), 1.4 nm MoS₂ pore (black), and 1.4 nm SiN_x pore (purple, Adapted with permission from ref (18). Copyright 2013 American Chemical Society) all in a 1 M KCl solution at transmembrane voltages of 180 mV, 180 mV, 180 mV, 300 mV, and 1 V and at bandwidths of 30 kHz, 10 kHz, 10 kHz, 10 kHz, and 500 kHz, respectively. Experiments for biological pores were done using an Axopatch 200B amplifier, a Teflon-supported lipid membrane (∼50–100 μm wide; DPhPC lipids), 10–30 kHz bandwidth, 1 M KCl, pH 7.5, and a forward bias voltage of 180 mV, as in ref (106). The solid-state SiN_x pore was built on a glass chip and measured with the VC100 high-bandwidth, low-noise voltage-clamp amplifier (Chimera Instruments, New York, NY, USA) which allowed for low-noise measurements at high bandwidth. A broad bandwidth of 500 kHz was required in order to fully resolve the fast translocations (∼22 μs)¹⁸ of poly(dT)₃₀ through the solid-state SiN_x pore. Notably, the positively charged constriction of ReFraC causes the negatively charged poly(dT)₅₀ to translocate with much slower (491 ± 114 μs) translocation times compared to MspA (17.7 ± 1.1 μs), which permitted to filter out more high-frequency noise. (d) Comparison of various figures of merit for different nanopore systems under typical experimental conditions. I_o indicates the open pore ionic current at the applied bias V.