pH Valve Based on Hydrophobicity Switching

Highly Efficient Gating of Electrically Actuated Nanochannels for Pulsatile Drug Delivery Stemming from a Reversible Wettability Switch

“…It is known that the electrowetting phenomenon will occur in hydrophobic nanopores by applying a sufficiently high transmembrane voltage that exceeds the critical bias. [4b,5b,17] Whereas here, when the nanochannels were in the closed state, the magnitude of the ionic current could remain at a fairly low level (≈1.2 nA; Figure S14a, Supporting Information) even when a high voltage of +8 V was applied (Figure a). This result was mainly due to the superhydrophobicity and the large film thickness making the doped PPy film highly efficient in impeding water‐soluble mass transport.…”

“…The simulation of the hydrophobic gating property of biological ion channels using synthetic nanochannels has attracted significant attention over recent years . For instance, Smirnov and co‐workers have developed a series of stimulus‐gated hydrophobic nanopores, which exhibit dramatic gating effects with a maximum ionic resistance change over six orders of magnitude . The gating ratio is much higher than that of the comparable gated nanochannels depending on stimuli‐induced variations of pore size or surface charge .…”

“…However, the reversible gating effects, especially the transition from wet to dry, are almost unfeasible in such hydrophobic nanopores with a large orifice or a long channel due to a high activation barrier. [5a–c]…”

“…In general, the wettability changes of nanochannels can be initiated by environmental stimuli when the nanochannels are engineered with functional films containing both stimuli‐responsive molecules and hydrophobic ones . The film with electroactive polypyrrole (PPy) doped with perfluorosulfonate ions is an innovative candidate to achieve an electrically actuated wettability switch.…”

“…The variation of ionic current was fairly reversible and stable under alternate applications of oxidation and reduction potentials, which indicated that a better repeatability of the gating behavior was achieved in our system compared with other comparable gated nanochannels. [5,6f] Herein, we used an ion‐gating ratio to quantitatively characterize the electric‐gating performance of nanochannels, which was defined to be the ratio of the ionic current value in the open ( I o , after applying the reduction potential to PPy film) and closed state ( I c , after applying the oxidation potential to PPy film). The calculated gating ratio from Figure a was as high as 1.2 × 10 4 at +1 V voltage in 1 × 10 −3 m KCl electrolyte, which was much higher than that of the existing reversibly gated nanochannels at comparable experimental conditions, to the best of our knowledge.…”