We have explored the role of electrokinetics in the spontaneous motion of platinum-gold nanorods suspended in hydrogen peroxide (H2O2) solutions that may arise from the bimetallic electrochemical decomposition of H2O2. The electrochemical decomposition pathway was confirmed by measuring the steady-state short-circuit current between platinum and gold interdigitated microelectrodes (IMEs) in the presence of H2O2. The resulting ion flux from platinum to gold implies an electric field in the surrounding solution that can be estimated from Ohm's Law. This catalytically generated electric field could in principle bring about electrokinetic effects that scale with the Helmholtz-Smoluchowski equation. Accordingly, we observed a linear relationship between bimetallic rod speed and the resistivity of the bulk solution. Previous observations relating a decrease in speed to an increase in ethanol concentration can be explained in terms of a decrease in current density caused by the presence of ethanol. Furthermore, we found that the catalytically generated electric field in the solution near a Pt/Au IME in the presence of H2O2 is capable of inducing electroosmotic fluid flow that can be switched on and off externally. We demonstrate that the velocity of the fluid flow in the plane of the IME is a function of the electric field, whether catalytically generated or applied from an external current source. Our findings indicate that the motion of PtAu nanorods in H2O2 is primarily due to a catalytically induced electrokinetic phenomenon and that other mechanisms, such as those related to interfacial tension gradients, play at best a minor role.
Ion transport in bionanopores is closely related to biological processes and can be regulated by various external stimulations. Multivalent ion as one of the stimulators shows a great ability in tuning the ion transport properties, while the mechanism is yet unclear. Here, inspired by this multivalent ion involved process, we propose a multivalent ion responsive symmetric hourglass polycarbonate nanopore. Addition of multivalent ion triggers formation of an abrupt bipolar junction inside the nanopore, and an ultrahigh ion current rectification ratio higher than 650 can be achieved. The ion transport property can be reversibly and significantly regulated via the reversible adsorption/desorption of multivalent ions on nanopore surface. This study provides the fundamentals to an understanding of the biological process and proposes an effective strategy to build smart nanofluidic devices.
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