Fig. 2. Single-channel detection of heparin (HP) oligosaccharides in the dpn range between tetrasaccharide dp4 and icosasaccharide dp20 (dpn, n = 4-20) analyzed individually and in mixture by successive introduction of HP oligosaccharides into the cis compartment.
a Schematics of the experimental setup with aerolysin inserted in a lipid bilayer (not to scale). The ionic current is recorded while applying a constant voltage. b Illustration of typical single nanopore current recording in presence of HP dp10. The current is blocked by the presence of the molecule inside the channel (translocation). For each translocation event the blocked current Ib, the open pore current I0 and the duration of event Tt are calculated. c Scatter plot for HP dp10 with the associated current histogram, translocation time histogram with logarithmic binning and the corresponding integrated probability (red curve and right axis). The black dot represents the first event represented on b. The distortion of the event cloud at short timescale is due to the signal distortion from the low-pass filtering of the signal. d Scatter plots obtained for different sizes of HP oligosaccharides when they were analyzed individually. Each dot represents the translocation of a single molecule. At least 2000 events were recorded for each molecule type. e Integrated probability of translocation for different sizes of HP oligosaccharides. Scatter plots of the f HP dp4, g mixture of HP dp4 and HP dp6, h mixture of HP dp4, HP dp6 and HP dp10, i mixture of HP dp4, HP dp6, HP dp10 and HP dp16, and j mixture of HP dp4, HP dp6, HP dp10, HP dp16 and HP dp20. The relative density of events on the plots is highlighted by the markers color: the brighter the dot, the denser the events. Progressive appearing of the deeper and longer events is clearly seen by the shift of the clouds of events towards long translocation times. All data were recorded in 4 M LiCl, 25 mM HEPES buffer and 1.0 mM EDTA at pH 7.5, 20.0 °C, at the bias voltage of +60 mV and using 43 μM of each oligosaccharide. For mixture analysis, oligosaccharides were added one by one at the same concentration (10 μM) to the cis chamber and the residual current was measured. Source data for this figure are provided as a Source Data file.