No abstract

Polymeric nanopores with fixed charges show ionic selectivity when immersed in aqueous electrolyte solutions. The understanding of the electrical interaction between these charges and the mobile ions confined in the inside nanopore solution is the key issue in the design of potential applications. The authors have theoretically described the effects that spatially inhomogeneous fixed charge distributions exert on the ionic transport and selectivity properties of the nanopore. A comprehensive set of one-dimensional distributions including the skin, core, cluster, and asymmetric cases are analyzed on the basis of the Nernst-Planck equations. Current-voltage curves, nanopore potentials, and transport numbers are calculated for the above distributions and compared with those obtained for a homogeneously charged nanopore with the same average fixed charge concentration. The authors have discussed if an appropriate design of the spatial fixed charge inhomogeneity can lead to an enhancement of the transport and selectivity with respect to the homogeneous nanopore case. Finally, they have compared the theoretical predictions with relevant experimental data.

It is well known that certain periodic structures built by repetition of elements produce sound attenuation effects as a consequence of the destructive interference of the scattered waves by these elements. The sound attenuation results that we got from transmission experiments with these kind of structures, so-called sonic crystals (SCs), led us to think that SCs could be used as an acoustic barrier. Until now, most of the transmission experiments with these periodic arrays of scatterers have been performed under controlled conditions, so how they would behave outdoors is still not well known. In this letter we present outdoor-experimental results for two-dimensional SCs and from these it can be concluded that periodic arrays of scatterers are a suitable device to reduce noise in free-field conditions.

We designed and characterized a cylindrical nanopore that exhibits high electrochemical current rectification ratios at low and intermediate electrolyte concentrations. For this purpose, the track-etched single cylindrical nanopore in polymer membrane was coated with a gold (Au) layer via electroless plating technique. Then, a non-homogeneous fixed charge distribution inside the Au-coated nanopore was obtained by incorporating thiol-terminated uncharged poly(N-isopropylacrylamide) chains in series to poly(4-vinylpyridine) chains, which were positively charged at acidic pH values. The functionalization reaction was checked by measuring the current-voltage curves prior to and after the chemisorption of polymer chains. The experimental nanopore characterization included the effects of temperature, adsorption of chloride ions, electrolyte concentration, and pH of the external solutions. The results obtained are further explained in terms of a theoretical continuous model. The combination of well-established chemical procedures (thiol and self-assembled monolayer formation chemistry, electroless plating, ion track etching) and physical models (two-region pore and Nernst-Planck equations) permits the obtainment of a new nanopore with high current rectification ratios. The single pore could be scaled up to multipore membranes of potential interest for pH sensing and chemical actuators.

We consider the screening of the negative charges (carboxylic acid groups) fixed on the surface of a conical-shaped track-etched nanopore by divalent magnesium (Mg 2+) and trivalent lanthanum (La 3+). The experimental current (I)voltage (V) curves and current rectification ratios allow discussing fundamental questions about the overcompensation of spatially-fixed charges by multivalent ions over nanoscale volumes. The effects of charge inversion or reversal on nanopore transport are discussed in mixtures of asymmetric electrolytes (LaCl 3 and MgCl 2 with KCl). In particular, pore charge inversion is demonstrated for La 3+ as well as for mixtures of this trivalent ion at low concentrations with monovalent potassium (K +) and divalent Mg 2+ ions at biologically relevant concentrations. It is found that small concentrations of multivalent ions can modulate the nanopore rectification and the transport of other majority ions in the solution. We study also the kinetics of the nanopore electrical recovery when the electrolyte solutions bathing the single-pore membrane are changed and show the hysteretic effects observed in the IV curves. Finally, we describe the hysteresis observed in the IV curves of CaCl 2 , MgCl 2, and BaCl 2 and mixtures. We also give a qualitative description of the effects of charge reversal on the pore rectification using the Nernst-Planck flux equations for multivalent ion mixtures.

ElsevierRamirez Hoyos, P.; Gómez Lozano, V.; Cervera, J.; Nasir, S.; Ali, M.; Ensinger, W.; Mafe, S. (2015). Energy conversion from external fluctuating signals based on asymmetric nanopores. Nano Energy. 16:375-382. doi:10.1016Energy. 16:375-382. doi:10. /j.nanoen.2015 AbstractElectrical transduction from fluctuating external signals is central to energy conversion based on nanoscale electrochemical devices and bioelectronics interfaces. We demonstrate theoretically and experimentally a significant energy transduction from white noise signals using the electrical rectification of asymmetric nanopores in polymeric membranes immersed in aqueous electrolyte solutions. Load capacitor voltages of the order of 1 V are obtained within times of the order of 1 min by means of nanofluidic diodes which convert zero time-average potentials of amplitudes of the order of 1 V into average net currents. We consider singlenanopore and multipore membranes to show that the conversion processes can be significantly increased by scaling. The results concern a wide range of operating electrolyte concentrations.Because these concentrations dictate the pore resistance, the tuning of the load capacitance to optimize the system response at each concentration is also addressed. Finally, the experimental results are described theoretically by using simple equivalent circuits with a voltage-dependent resistance in series with a load capacitance.

The chemical and physical input signals characteristic of micro-and nanofluidic devices operating in ionic solutions should eventually be translated into output electric currents and potentials that are monitored with solid-state components. This crucial step requires the design of hybrid circuits showing robust electrical coupling between ionic solutions and electronic elements. We have studied experimentally and theoretically the connectivity of the nanofluidic diodes in single pore and multipore membranes with conventional capacitor systems for the cases of constant, periodic, and white noise input potentials. The experiments demonstrate the reliable operation of these hybrid circuits over a wide range of membrane resistances, electrical capacitances, and solution pH values. The model simulations are based on phenomenological equations that provide a convenient description of the electrical circuit operation. The results should contribute to advance signal transduction and processing using nanopore-based biosensors and bioelectronic interfaces.

ElsevierRamirez Hoyos, P.; Gómez Lozano, V.; Ali, M.; Ensinger, W.; Mafé, S. (2013) ABSTRACTWe have studied experimentally and theoretically the rectifying properties of a single asymmetric nanopore functionalized with amphoteric lysine groups and characterized the net current obtained with zero-average time dependent potentials. The pH-controlled rectification phenomena may be relevant to bio-electrochemistry, pH sensing and regulation, and energy conversion.