Fig. 5. (a) I–V characteristics of the switchable nanochannel modulated by MAP5 and Hg²⁺. (b) Stability and responsive switching ability of the tunable system. Reversible variation of potassium ion current was measured at a negative potential (–2 V) with the alternate addition of Hg²⁺ and MAP5. (c) Laser scanning confocal microscopy observation of the rhodamine B derivative fluorescent pillar[5]arene assembled on the HDA-modified nanochannel surface and competition with Hg²⁺. The “on–off” fluorescence signal indicates that MAP5 can assemble on the nanochannel and is removed by Hg²⁺.