Fig. 2: Comparison between WT α-HL and MspA-M for single [AuCl4]− sensing.
a Geometric comparison between WT α-HL (red) and MspA-M (blue). Yellow spots indicate the location of methionine in the pore. b Representative binding events from a single [AuCl4]− within a WT α-HL or a MspA-M nanopore at +100 mV, respectively. c Event-amplitude (ΔI) histograms with Gaussian fitting for single [AuCl4]− bindings within a WT α-HL (red) or an MspA-M (blue) nanopore. The [AuCl4]− sensing performance is significantly improved with MspA-M showing a deeper blockage depth and a narrower distribution width (WT α-HL: 5.6 ± 0.3 pA; MspA-M: 11.3 ± 0.2 pA). d Log dwell-time histograms for WT α-HL (red) and MspA-M (blue) for single [AuCl4]− bindings. Single [AuCl4]− binding within MspA-M shows a systematically reduced event dwell time, possibly due to a sharper restriction from the conical MspA pore. The statistical data in c and d were taken from 10 min continuous electrophysiology recording at +100 mV with 1 µM HAuCl4 in cis. e–g Representative traces for [AuCl4]− ions binding in MspA-M at +20 mV (e), +100 mV (f), and +180 mV (g) with 1 μM HAuCl4 in cis. All traces (e–g) were digitally filtered with a 200 Hz low-pass Bessel filter (eight-pole) by Clampfit so that the shallow binding events in e could be presented. h Plot of the mean blockage depth for [AuCl4]− ions in MspA-M and WT α-HL at different voltages (Supplementary Table 4). Mean ± Standard Deviation in h are from three independent experiments (N = 3) with 15 min recording for WT α-HL and 5 min recording for MspA-M at each condition. An extended acquisition time for WT α-HL was taken to compensate the reduced event counts compared to that from MspA-M.
