Fig. 4: Stochastic sensing of L-homocysteine by Au(III) embedded MspA-M.
a The chemical structure of L-homocysteine (Hcy), a homologue of Cys with an extra carbon in its structure (green labeled portion). b Binding of Hcy with [AuCl4]− embedded MspA-M. The demonstrated trace was recorded with a +100 mV applied voltage when 4 μM HAuCl4 in cis and 40 μM Hcy in trans were present simultaneously. Resistive pulse signals in the trace result from binding of a [AuCl4]− or binding of a Hcy by taking the bound Au(III) as an atomic bridge. Green diamonds mark the events of Hcy. The gray star marks the events of [AuCl4]−. Other unlabeled events are background signals as described in Supplementary Fig. 15. c A representative Hcy blockage event. Similar to Fig. 3E, a representative Hcy blockage event is composed of three states as described in Fig. 3b. Characteristic jitter signals can be recognized as state 1SH. However, the mean blockage amplitude of state 1SH for Hcy is systematically deeper than that of Cys. d The scatter plot of the ΔI/I0 vs the dwell time from events of [AuCl4]− and Hcy binding. e The histogram of ΔI/I0 for single [AuCl4]− bindings and Hcy bindings. The statistical data in d and e were derived from a continuous 10 min recording with a +100 mV applied voltage (Supplementary Tables 7 and 8). f Simultaneous discrimination of Hcy and Cys with [AuCl4]− embedded MspA-M. The demonstrated trace was recorded with a +100 mV applied voltage when 4 μM HAuCl4 in cis were present. Cys and Hcy were placed in trans with a concentration of 20 μM for each analyte. Red triangles mark the events of Cys while green diamonds mark those of Hcy. The gray star marks the event of [AuCl4]−. A zoomed-in view of events from Hcy or Cys were demonstrated in the dotted box. g The scatter plot of the ΔI/I0 vs the dwell time with the corresponding amplitude histogram from Hcy and Cys sensing. The plot data were from a continuous 10 min recording as described in f.
