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Fig. 2 | Nanoscale Research Letters

Fig. 2

From: A Protein Nanopore-Based Approach for Bacteria Sensing

Fig. 2

The working principle of the α-HL nanopore-based detection of bacteria at single-particle level. The negative electric potential on the trans side of a lipid membrane containing a single α-HL nanopore drives negatively charged bacteria into the nanopore. Within a spherical symmetry formalism, the absolute value of the electrophoretic force (F elp) acting on the bacteria is proportional to the negative electric charge on bacterial surface (Q) and the electric field (E) measured in bulk at a radial distance (r) from the pore, which emanates from the applied transmembrane potential (ΔV) [44]. In the inset formula, d and l represent the pore’s diameter and length. The bacteria-nanopore collisions at the lumen entrance of the α-HL determine brief obstructions of the nanopore’s permeating pathway, seen as reversible blockades of the ionic current, further measured with a sensitive current amplifier. The idealized trace inset allows us to define the main characteristics which are subsequently used to quantify the single bacteria-nanopore interactions, namely the extent of the ionic current blockade (ΔI block = I blocked pore − I free pore), average time of intervals measured between successive blockade events (τ on) and average time spent by the nanopore in the blocked state, following its interaction with a bacterium (τ off). Note that bacteria and the α-HL protein are not drawn to scale

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