Figure 4.

(a) Typical set-up for ion transport-based sensing and schematic illustration of the proposed three-layer model of the charged layer, double layer, and bulk layer. Reprint with permission from ref (24). (b) Schematic illustration of an MICR-based biosensor for online measurement of cerebral ATP concentration. Reprint with permission from ref (25). (c) Schematic illustration of single nanoparticle collision at the orifice of a nanopipette in two modes. Collision and stay produces staircase current. Collision and leave produces spike currents. Reprint with permission from ref (26).