Waldemar A. Marmisollé

Self-Assembled Monolayers of NH2-Terminated Thiolates: Order, pKa, and Specific Adsorption

Self-assembled monolayers (SAMs) of amino-terminated alkanethiols on Au were characterized by a combination of electrochemical (LSV, CV, and EIS) and spectroscopic (XPS and SER) techniques. Clear correlations were obtained between the apparent surface pKa values determined by impedimetric titrations and order parameters such as the content of trans conformers in the SAMs. These results contrast with previous studies that exhibit dispersions of up to 6 pH units in the reported pKa values. In addition, we determined that inorganic and organic phosphate species bind specifically to these SAMs mediating adsorption and heterogeneous electron transfer of positively charged macromolecules such as cytochrome c.

Nanofluidic Diodes with Dynamic Rectification Properties Stemming from Reversible Electrochemical Conversions in Conducting Polymers

The use of solid state nanochannels as nanofluidic diodes is currently a topic of large interest in nanotechnology. Particularly, there is a focus in the development of nanochannels with surface functionalities that make them responsive to multiple environmental variables. Here, we present for the first time the construction of electrochemical potential- and pH-responsive nanofluidic diodes using a novel approach based on a controlled electrochemical polymerization of aniline on gold-coated polycarbonate asymmetric nanochannels. The polyaniline-modified nanochannels showed three different levels of reversible ionic rectification corresponding to the degrees of oxidation of the conducting polymer. Our results demonstrate that this strategy enables an accurate and reversible control of the rectification properties due to the well-defined and predictable electrochemical conversion of charged species generated on the pore walls. We envision that these results will create novel avenues to fabricate electrochemically modulated nanofluidic diodes using conducting polymers integrated into single conical nanopores.

Electrochemical Aging of Poly(aniline) and Its Ring Substituted Derivatives

Aniline and methyl, ethyl, propyl, and methoxy ring substituted derivatives have been polymerized by electrochemical methods. The reduction of the film produces aging of the polymers. This is followed by the changes in the current/potential profile of the voltammetric response. The effect of the substituents produces changes in both the extent and the rate of aging. The rate of aging can be represented by a Roginsky-Zeldovich or Elovich type of kinetics characterized by a pseudo zero order rate constant and a self-inhibiting parameter. Both parameters and the extent of aging are related to the free volume available for the different types of polymers.

The coupling among electron transfer, deformation, screening and binding in electrochemically active macromolecules.

Experimental data are presented demonstrating that electrochemically active macromolecules show a coupling among electron transfer, deformation, screening and binding. The work includes dependence of the redox potential of synthetic and natural electrochemically active polymers on the electrolyte pH (electron transfer-binding coupling), the changes in volume during the redox switching of synthetic electrochemically active polymers (deformation-electron transfer coupling) and the changes in the macromolecular conformation during the acid-base titration of polyelectrolytes and proteins (deformation-binding coupling). A simple equilibrium statistical thermodynamic model is presented that allows explaining these couplings effects. The model is based on the assumption that a macromolecule is composed of segments of different length that may bind species present in the external solution and that also contain redox centers that may be oxidized and reduced. The partition function of the system is obtained, and from it the expressions for the redox potentials, the total length and the chemical potential of the bound species are obtained. Simple calculations shows that the model satisfactorily explains the qualitative behavior of the experimental results.

An All‐Plastic Field‐Effect Nanofluidic Diode Gated by a Conducting Polymer Layer

The design of an all-plastic field-effect nanofluidic diode is proposed, which allows precise nanofluidic operations to be performed. The fabrication process involves the chemical synthesis of a conductive poly(3,4-ethylenedioxythiophene) (PEDOT) layer over a previously fabricated solid-state nanopore. The conducting layer acts as gate electrode by changing its electrochemical state upon the application of different voltages, ultimately changing the surface charge of the nanopore. A PEDOT-based nanopore is able to discriminate the ionic species passing through it in a quantitative and qualitative manner, as PEDOT nanopores display three well-defined voltage-controlled transport regimes: cation-rectifying, non-rectifying, and anion rectifying regimes. This work illustrates the potential and versatility of PEDOT as a key enabler to achieve electrochemically addressable solid-state nanopores. The synergism arising from the combination of highly functional conducting polymers and the remarkable physical characteristics of asymmetric nanopores is believed to offer a promising framework to explore new design concepts in nanofluidic devices.

Phosphate-Responsive Biomimetic Nanofluidic Diodes Regulated by Polyamine-Phosphate Interactions: Insights into Their Functional Behavior from Theory and Experiment

There is currently high interest in developing nanofluidic devices whose iontronic output is defined by biological interactions. The fabrication of a phosphate responsive nanofluidic diode by using the biological relevant amine-phosphate interactions is shown. The fabrication procedure includes the modification of a track-etched asymmetric (conical) nanochannel with polyallylamine (PAH) by electrostatic self-assembly. PAH is the arcaetypical model of polyamine and it is further used to address the nanochannels with phosphate responsivity. In order to explore the influence that phosphate in solution has in the conductance of the modified nanochannels, current-voltage measurements using different concentrations of phosphates are performed. Furthermore, to have a complete physicochemical understanding of the system, experimental data is analyzed using a continuous model based on Poison-Nernst-Planck equations and compared with results obtained from stochastic Monte Carlo simulations.

Proton-Gated Rectification Regimes in Nanofluidic Diodes Switched by Chemical Effectors

During the last decade, nanofluidic devices based on solid-state nanopores and nanochannels have come into scene in materials science and will not leave anytime soon. One of the main reasons for this is the excellent control over ionic transport exerted by such devices that promises further important advances when integrated into more complex molecular devices. As a result, pH, temperature, and voltage-regulated devices have been obtained. However, nowadays, there is still a necessity for molecule-driven nanofluidic devices. Here, a sugar-regulated pH-responsive nanofluidic diode is presented obtained by surface modification of conical polycarbonate nanochannels with electropolymerized 3-aminophenylboronic acid. Control over the ionic transport has been achieved by a successful decoration of asymmetric nanochannels with integrated molecular systems. The as-synthesized boronate-appended zwitterionic polymer exhibits an acid-base equilibrium that depends on the concentration of sugar, which ultimately acts as a chemical effector setting different pH-dependent rectification regimes. As a result, the same nanodevice can perform completely different proton-regulated nanofluidic operations, i.e., anion-driven rectification, cation-driven rectification, and no rectification, by simply varying the concentration of fructose in the electrolyte solution.

Reversible modulation of the redox activity in conducting polymer nanofilms induced by hydrophobic collapse of a surface-grafted polyelectrolyte

We present the covalent modification of a Pani-like conducting polymer (polyaminobenzylamine, PABA) by grafting of a polyelectrolyte brush (poly [2-(methacryloyloxy)-ethyl-trimethylammonium chloride], PMETAC). As PABA has extra pendant amino moieties, the grafting procedure does not affect the backbone nitrogen atoms that are implicated in the electronic structure of the conducting polymers. Moreover, perchlorate anions interact very strongly with the quaternary ammonium pendant groups of PMETAC through ion pairing. Therefore, the grafting does not only keep the electroactivity of PABA in aqueous solutions but it adds the ion-actuation properties of the PMETAC brush to the modified electrode as demonstrated by contact angle measurements and electrochemical methods. In this way, the conjugation of the electron transfer properties of the conducting polymer with the anion responsiveness of the integrated brush renders perchlorate actuation of the electrochemical response. These results constitute a rational integration of nanometer-sized polymer building blocks that yields synergism of functionalities and illustrate the potentialities of nanoarchitectonics for pushing the limits of soft material science into the nanoworld.