Graphene-Paper-Based Electrodes on Plastic and Textile Supports as New Platforms for Amperometric Biosensing

The possibility of exfoliating graphite into graphene sheets allows the researchers to produce a material, termed “graphene paper” (G-paper), conductive as graphite but more flexible and processable. G-paper is already used for electronic applications, like conductors, antennas, and heaters, outperforming metal conductors thanks to its high flexibility, lightness, chemical stability, and compatibility with polymeric substrates. Here, the effectiveness in the use of G-paper for the realization of electrodes on flexible plastic substrates and textiles, and their applicability as amperometric sensors are demonstrated. The performance of these devices is compared with commercial platforms made of carbon-based inks, finding that they outperform commercial devices in sensing nicotinamide adenine dinucleotide (NADH), a key molecule for enzymatic biosensing; the electrodes can achieve state-of-the-art sensitivity (107.2 μA mm−1 cm−2) and limit of detection (0.6 × 10−6 m) with no need of additional functionalization. Thanks to this property, the stable deposition of a suitable enzyme, namely lactate dehydrogenase, on the electrode surface is used as a proof of concept of the applicability of this new platform for the realization of a biosensor. The possibility of having a single material suitable for antennas, electronics, and now sensing opens new opportunities for smart fabrics in wearable electronic applications

Graphene and related materials in hierarchical fiber composites: Production techniques and key industrial benefits

Fiber-reinforced composites (FRC) are nowadays one of the most widely used class of high-tech materials. In particular, sporting goods, cars and the wings and fuselages of airplanes are made of carbon fiber reinforced composites (CFRC). CFRC are mature commercial products, but are still challenging materials. Their mechanical and electrical properties are very good along the fiber axis, but can be very poor perpendicular to it; interfacial interactions have to be tailored for specific applications to avoid crack propagation– and delamination; fiber production includes high-temperature treatments of adverse environmental impact, leading to high costs. Recent research work shows that the performance of CFRC can be improved by addition of graphene or related 2-dimensional materials (GRM). Graphene is a promising additive for CFRC because: 1) Its all-carbon aromatic structure is similar to the one of carbon fiber (CF). 2) Its 2-dimensional shape, high aspect ratio, high flexibility and mechanical strength allow it to be used as a coating on the surface of fiber, or as a mechanical/electrical connection between different fiber layers. 3) Its tunable surface chemistry allows its interaction to be enhanced with either the fiber or the polymer matrix used in the composite and 4) in contrast to carbon fibers or nanotubes, it is easily produced on a large scale at room temperature, without metal catalysts. Here, we summarize the key strategic advantages that could be obtained in this way, and some of the recent results that have been obtained in this field within the Graphene Flagship project and worldwide

Self-encapsulation of organic thin film transistors by means of ion implantation

Long-term stability of devices based on organic materials is still impeding the diffusion of these structures in real applications. In this paper we have investigated the effects of low energy, combined, ion implantation (N and Ne) in the evolution of the electrical performances of pentacene-based Organic Thin Film Transistors (OTFTs) over time by means of current-voltage and photocurrent spectroscopy analyses. We have demonstrated that the selected combination of ions allows reducing the degradation of charge carriers mobility, and also stabilization of the devices threshold voltage over a long time (over 2000 h). \ua9 2015 Elsevier B.V. All rights reserved \ua9 2015 Elsevier B.V. All rights reserved

Spectroscopic investigation of the semiconductor molecular packing in fully operational organic thin-film transistors

none7noneB.Fraboni; A.Scidà; A.Cavallini; P.Cosseddu; A.Bonfiglio; S.Milita; M.NastasiB.Fraboni; A.Scidà; A.Cavallini; P.Cosseddu; A.Bonfiglio; S.Milita; M.Nastas

Discharging behavior of confined bipolar electrodes: Coupled electrokinetic and electrochemical dynamics

In this study we numerically investigate the intimately coupled transient electrokinetic and electrochemical dynamics of a nanoconfined bipolar electrode system, using experimental results to guide our analysis. Our recently developed 2D numerical model implements the Poisson-Nernst-Planck-Stokes system of equations to describe nanoscale chemical species transport by advection, migration, and diffusion, as well as the presence of both homogenous and heterogeneous reactions. By eschewing the assumption of electroneutrality and resolving diffuse-charge screening effects, our model uniquely accounts for a wide range of nonlinear transient effects including bipolar electrode (BPE) surface polarization, Faradaic charge accumulation, induced-charge electroosmotic flow, and ion concentration polarization. Using this model, we demonstrate that upon the removal of a polarizing electric field, excess accumulated charge at a BPE surface electrochemically discharges following the capacitive relaxation of diffuse space charge in the electrical double layers (EDLs) surrounding the BPE extremities. These EDLs continue to polarize the BPE as they relax by a process of drift-diffusion, wherein the counter-ionic space charge at each pole promotes a large influx of oppositely charged ions to restore electroneutrality. We numerically reproduced this electrokinetic enhancement effect that was first observed in a recently reported experimental system in which charged fluorophores were used as tracer molecules. Our results also support experimental evidence that, following capacitive EDL relaxation, nanoconfined BPEs can exhibit pseudocapacitance-like discharging behavior that is localized to a single end of the electrode; we experimentally linked this localization to surface oxidation of the anodic BPE pole under the applied field. In addition to providing important insight into the interplay between nanoscale electrokinetic and electrochemical phenomena that govern transient electrode processes, our model and the results presented in this work reinforce the notion that the domain of bipolar electrochemistry constitutes a promising frontier for developing “wirelessly” tunable charge storage and visual detection approaches which exploit both electrokinetic and Faradaic mechanisms

Modeling Faradaic Reactions and Electrokinetic Phenomena at a Nanochannel-Confined Bipolar Electrode

We present the most comprehensive two-dimensional numerical model to date for a nanoconfined bipolar electrochemical system. By accounting for the compact Stern layer and resolving the diffuse part of the electrical double layer at the bipolar electrode (BPE) surface and channel walls, our model captures the impact of surface polarization and ionic charge-screening effects on the heterogeneous charge-transfer kinetics, as well as nonlinear electrokinetic transport phenomena such as induced-charge electroosmosis and concentration polarization. We employ the Poisson-Nernst-Planck and Stokes flow system of equations, unified with generalized Frumkin-Butler-Volmer reaction kinetics, to describe water electrolysis reactions and the resulting transport of ions and dissolved gases in the confined BPE system. Our results demonstrate that under a sufficiently large applied electric field, the rapid reaction kinetics on our Pt BPE dynamically transition from charge-transfer-limited to mass-transfer-limited temporal regimes as regions depleted of redox species form and propagate outward from the respective BPE poles. This phenomenon was visualized experimentally with a pH-sensitive fluorescein dye and showed excellent phenomenological agreement with our numerical calculations, providing a foundation for further understanding and developing bipolar electrochemical processes in confined geometries. We introduce two prospective applications arising from our work: (1) a hybrid hydrodynamic/electrochemical peristaltic pump and (2) deducing information about chemical kinetics through simulation