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We show that ionic conduction properties of a multipore nanofluidic memristor can be controlled not only by the amplitude and frequency of an external driving signal but also by chemical gating based on the electrolyte concentration, presence of divalent and trivalent cations, and multi-ionic systems in single and mixed electrolytes. In addition, we describe the modulation of current rectification and hysteresis phenomena, together with neuromorphic conductance responses to voltage pulses, in symmetric and asymmetric external solutions. In our case, memristor conical pores act as nanofluidic diodes modulated by ionic solution characteristics due to the surface charge-regulated ionic transport. The above facts suggest potential sensing and actuating applications based on the conversion between ionic and electronic signals in bioelectrochemical hybrid circuits. [ABSTRACT FROM AUTHOR]

We have arranged two multipore membranes with conical nanopores in a three-compartment electrochemical cell. The membranes act as tunable nanofluidic diodes whose functionality is entirely based on the pH-reversed ion current rectification and does not require specific surface functionalizations. This electrochemical arrangement can display different electrical behaviors (quasi-linear ohmic response and inward/outward rectifications) as a function of the electrolyte concentration in the external solutions and the applied voltage at the pore tips. The multifunctional response permits to implement different logical responses including NOR and INHIBIT functions.

We have studied experimentally the electrical conductance–voltage curves of negatively and positively charged conical nanopores bathed in ionic solutions with monovalent, divalent, and trivalent cations at electrochemically and biologically relevant ionic concentrations. To better understand the interaction between the pore surface charge and the mobile ions, both single salts and salt mixtures have been considered. We have paid attention to the effects on the conductance of the cation valency, the pore charge asymmetry, and the pore charge inversion phenomena due to trivalent ions, both in single salts and salt mixtures. In addition, we have described how small concentrations of multivalent ions can tune the nanopore conductance due to monovalent majority ions, together with the effect of these charges on the additivity of ionic conductance and fluoride-induced negative differential conductance phenomena. This compilation and discussion of previously presented experimental data offers significant insights on the interaction between fixed and mobile charges confined in nanoscale volumes and should be useful in establishing and checking new models for describing ionic transport in the vicinity of charged surfaces. [ABSTRACT FROM AUTHOR]

The diffusion of two similar molecular weight proteins, bovine serum albumin (BSA) and bovine haemoglobin (BHb), through nanoporous charged membranes with a wide range of pore radii is studied at low ionic strength. The effects of the solution pH and the membrane pore diameter on the pore permeability allow quantifying the electrostatic interaction between the charged pore and the protein. Because of the large screening Debye length, both surface and bulk diffusion occur simultaneously. By increasing the pore diameter, the permeability tends to the bulk self-diffusion coefficient for each protein. By decreasing the pore diameter, the charges on the pore surface electrostatically hinder the transport even at the isoelectric point of the protein. Surprisingly, even at pore sizes 100 times larger than the protein, the electrostatic hindrance still plays a major role in the transport. The experimental data are qualitatively explained using a two-region model for the membrane pore and approximated equations for the pH dependence of the protein and pore charges. The experimental and theoretical results should be useful for designing protein separation processes based on nanoporous charged membranes.

pH-dependent electrochemical rectification in a protein ion channel reconstituted on a planar phospholipid membrane is reported. The measurements performed at single-channel level show that the electric current is controlled by the protein fixed charge and it could be tuned by adjusting the local pH.

An experiment with a filled helium balloon in a car shows students the true nature of centrifugal force. Most students believe that centrifugal force moves objects to the outside of the circle, however this experiment demonstrates that objects move towards the center of curvature of the trajectory.