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

Tuneable conductivity at extreme electric fields in ZnO tetrapod-silicone composites for high-voltage power cable insulation

Resistive Field Grading Materials (RFGM) are used in critical regions in the electrical insulation system of high-voltage direct-current cable systems. Here, we describe a novel type of RFGM, based on a percolated network of zinc oxide (ZnO) tetrapods in a rubber matrix. The electrical conductivity of the composite increases by a factor of 108 for electric fields > 1\ua0kV\ua0mm-1, as a result of the highly anisotropic shape of the tetrapods and their significant bandgap (3.37\ua0eV). We demonstrate that charge transport at fields < 1\ua0kV\ua0mm-1 is dominated by thermally activated hopping of charge carriers across spatially, as well as energetically, localized states at the ZnO-polymer interface. At higher electric fields (> 1\ua0kV\ua0mm-1) band transport in the semiconductive tetrapods triggers a large increase in conductivity. These geometrically enhanced ZnO semiconductors outperform standard additives such as SiC particles and ZnO micro varistors, providing a new class of additives to achieve variable conductivity in high-voltage cable system applications

Graphene oxide–polysulfone filters for tap water purification, obtained by fast microwave oven treatment

The availability of clean, pure water is a major challenge for the future of our society. 2-Dimensional nanosheets of GO seem promising as nanoporous adsorbent or filters for water purification; however, their processing in macroscopic filters is challenging, and their cost\ua0vs.\ua0standard polymer filters is too high. Here, we describe a novel approach to combine graphene oxide (GO) sheets with commercial polysulfone (PSU) membranes for improved removal of organic contaminants from water. The adsorption physics of contaminants on the PSU-GO composite follows Langmuir and Brunauer–Emmett–Teller (BET) models, with partial swelling and intercalation of molecules in between the GO layers. Such a mechanism, well-known in layered clays, has not been reported previously for graphene or GO. Our approach requires minimal amounts of GO, deposited directly on the surface of the polymer, followed by stabilization using microwaves or heat. The purification efficiency of the PSU-GO composites is significantly improved\ua0vs.\ua0benchmark commercial PSU, as demonstrated by the removal of two model contaminants, rhodamine B and ofloxacin. The excellent stability of the composite is confirmed by extensive (100 hours) filtration tests in commercial water cartridges

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 7 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

Accurate chemical analysis of graphene-based materials using X-ray photoelectron spectroscopy

A simple, fast and general protocol for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data provides accurate estimations of chemical species in graphene and related materials (GRMs). XPS data are commonly used to estimate the quality of and defects in graphene and graphene oxide (GO), by comparing carbon and oxygen 1s XPS peaks, obtaining an O/C ratio. This approach, however, cannot be used in the presence of extraneous oxygen contamination. The protocol, based on quantitative line-shape analysis of C 1s signals, uses asymmetric pseudo- Voigt line-shapes (APV), in contrast to Gaussian-based approaches conventionally used in fitting XPS spectra, thus allowing better accuracy in quantifying C 1s contributions from graphitic carbon (sp2), defects (sp3 carbon), carbons bonded to hydroxyl and epoxy groups, and from carbonyl and carboxyl groups. The APV protocol was evaluated on GRMs with O/C ratios ranging from 0.02 to 0.30 with film thicknesses from monolayers to bulk-like (>30nm) layers and also applied to previously published data, showing better results compared to those from conventional XPS fitting protocols. Based uniquely on C 1s data, the APV protocol can quantify O/C ratio and the presence of specific functional groups in GRMs even on SiOx, substrates, or in samples containing water

Benchmarking of graphene-based materials: Real commercial products versus ideal graphene

There are tens of industrial producers claiming to sell graphene and related materials (GRM), mostly as solid powders. Recently the quality of commercial GRM has been questioned, and procedures for GRM quality control were suggested using Raman Spectroscopy or Atomic Force Microscopy. Such techniques require dissolving the sample in solvents, possibly introducing artefacts. A more pragmatic approach is needed, based on fast measurements and not requiring any assumption on GRM solubility. To this aim, we report here an overview of the properties of commercial GRM produced by selected companies in Europe, USA and Asia. We benchmark: (A) size, (B) exfoliation grade and (C) oxidation grade of each GRM versus the ones of \u27ideal\u27 graphene and, most importantly, versus what reported by the producer. In contrast to previous works, we report explicitly the names of the GRM producers and we do not re-dissolve the GRM in solvents, but only use techniques compatible with industrial powder metrology. A general common trend is observed: Products having low defectivity (%sp 2 bonds >95%) feature low surface area (<200 m 2 g -1 ), while highly exfoliated GRM show a lower sp 2 content, demonstrating that it is still challenging to exfoliate GRM at industrial level without adding defects

Application of graphene-based flexible antennas in consumer electronic devices

We describe the fabrication and characterization of Near-Field Communication (NFC) devices based on highly flexible, carbon-based antennas composed of stacked graphene multilayers. This material features a high value of conductivity (4.20 * 10 5 S/m) comparable to monocrystalline graphite, but is much more flexible and processable. We first studied the replacement of metal with carbon antennas using computer modeling, to select the best design. Then we manufactured several devices to be used according to the communication protocol ISO/IEC 15693. The inductance of the G-paper antennas was tested before and after hundreds of thousands of bending cycles at bending radii of 45 and 90 mm. During bending the self-resonance frequency and inductance peak showed minimal variation and the resistance at 1 MHz changed from 33.09 Ω to 34.18 Ω outperforming standard, commercial metallic antennas. The devices were successfully tested by exchanging data with a smartphone and other commercial NFC readers, matching the performance of standard, commercial metallic antennas. The graphene antennas could be deposited on different standard polymeric substrates or on textiles. Smart cards, flexible NFC tags and wearable NFC bracelets were prepared in this way to be used in electronic keys, business cards and other typical NFC applications

Reduced Graphene Oxide: fundamentals and applications

In this paper we report our recent studies on the fundamental physical/chemical properties of supported reduced Graphene Oxide (rGO) obtained either via standard thermal annealing or under extreme-UV (EUV) light exposure alongside with investigations on its possible technological applications. rGO has been studied by X-ray Photoelectron Spectroscopy (XPS), micro-Raman Spectroscopy (μRS), and Optical Microscopy. rGO reduction degree has been calibrated on the basis of its color contrast (CC) providing a handy tool to quantitatively determine the fraction of sp The original choice of using EUV instead of UV light to photo-reduce supported GO is not only advantageous in terms of reduction efficiency but it also allows to introduce the concept of EUV photolithography (today limited to the silicon technology only) for the processing of graphene-based materials. Here we demonstrate resistless sub-micrometer GO photo-patterning over large areas ( 10 mm 2 ) This result is a relevant upgrade for the graphene-based technology that can take advantage, in this way, from the entire know-how of the EUV-based technology in view of an eco-sustainable all-carbon technology

Evolution of the size and shape of 2D nanosheets during ultrasonic fragmentation

journal_title: 2D Materials article_type: paper article_title: Evolution of the size and shape of 2D nanosheets during ultrasonic fragmentation copyright_information: © 2017 IOP Publishing Ltd date_received: 2016-09-12 date_accepted: 2017-01-06 date_epub: 2017-02-01The research leading to these results has received funding from the European Union Horizon 2020 Framework Programme under grant agreement n°696656 Graphene Core1 and the EC Marie-Curie ITN-iSwitch (GA no. 642196). NMP is also supported by the European Research Council PoC 2015 "Silkene" No. 693670, by the European Commission H2020 with the Fet Proactive "Neurofibres" No. 732344

Visualizing Graphene Based Sheets by Fluorescence Quenching Microscopy

Graphene based sheets have stimulated great interest due to their superior mechanical, electrical and thermal properties. A general visualization method that allows quick observation of these single atomic layers would be highly desirable as it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies. Here we report that graphene based sheets can be made highly visible under a fluorescence microscope by quenching the emission from a dye coating, which can be conveniently removed afterwards by rinsing without disrupting the sheets. Current imaging techniques for graphene based sheets rely on the use of special substrates. In contrast, the fluorescence quenching mechanism is no longer limited by the types of substrates. Graphene, reduced graphene oxide, or even graphene oxide sheets deposited on arbitrary substrates can now be readily visualized by eye with good contrast for layer counting. Direct observation of suspended sheets in solution was also demonstrated. The fluorescence quenching microscopy offers unprecedented imaging flexibility and could become a general tool for characterizing graphene based materials.Comment: J. Am. Chem. Soc., Article ASA