Showing papers by "Cinzia Casiraghi published in 2017"

Water-based and biocompatible 2D crystal inks for all-inkjet-printed heterostructures

Abstract: Exploiting the properties of two-dimensional crystals requires a mass production method able to produce heterostructures of arbitrary complexity on any substrate. Solution processing of graphene allows simple and low-cost techniques such as inkjet printing to be used for device fabrication. However, the available printable formulations are still far from ideal as they are either based on toxic solvents, have low concentration, or require time-consuming and expensive processing. In addition, none is suitable for thin-film heterostructure fabrication due to the re-mixing of different two-dimensional crystals leading to uncontrolled interfaces and poor device performance. Here, we show a general approach to achieve inkjet-printable, water-based, two-dimensional crystal formulations, which also provide optimal film formation for multi-stack fabrication. We show examples of all-inkjet-printed heterostructures, such as large-area arrays of photosensors on plastic and paper and programmable logic memory devices. Finally, in vitro dose-escalation cytotoxicity assays confirm the biocompatibility of the inks, extending their possible use to biomedical applications. Device fabrication can be realized via inkjet printing of water-based 2D crystals.

Edge Functionalization of Structurally Defined Graphene Nanoribbons for Modulating the Self-Assembled Structures

Abstract: Edge functionalization of bottom-up synthesized graphene nanoribbons (GNRs) with anthraquinone and naphthalene/perylene monoimide units has been achieved through a Suzuki coupling of polyphenylene precursors bearing bromo groups, prior to the intramolecular oxidative cyclo-dehydrogenation. High efficiency of the substitution has been validated by MALDI-TOF MS analysis of the functionalized precursors and FT-IR, Raman, and XPS analyses of the resulting GNRs. Moreover, AFM measurements demonstrated the modulation of the self-assembling behavior of the edge-functionalized GNRs, revealing that GNR-PMI formed an intriguing rectangular network. This result suggests the possibility of programming the supramolecular architecture of GNRs by tuning the functional units.

Growing N-doped multiphase TiO2 nanocomposites on reduced graphene oxide: Characterization and activity under low energy visible radiation

Abstract: Reduced graphene oxide (G) was used as a platform to grow a mixed catalyst made of brookite and rutile nanoparticles doped with nitrogen, resulting in excellent performance for the oxidation of 4-nitrophenol (4-NP) in water under low energy (>425 nm) radiation The samples were fully characterized by X-Ray Diffractometry (XRD), Raman Spectroscopy, Electron Microscopy, X-Ray photoelectron spectroscopy (XPS), photoluminescence (PL), Z-potential analysis, UV–vis Diffuse Reflectance Spectrophotometry (UV–vis DRS), and porosimetry The improved hole-electron separation, demonstrated by PL, is boosted by the exceptional properties of reduced graphene oxide, which attracts and conveys electrons to dissolved oxygen, in turn initiating the oxidation process The optimal amount of reduced graphene oxide was found to be 1% w/w based on 4-nitrophenol (4-NP) conversion rates No leaching of carbon into water was revealed, even under irradiation, pointing to the suitability of the composite catalyst in water

Aqueous dispersions of nanostructures formed through the self-assembly of iminolipids with exchangeable hydrophobic termini.

Abstract: The addition of amines to an aldehyde surfactant, which was designed to be analogous to didodecyldimethylammonium bromide, gave exchangeable “iminolipids” that self-assembled to give stable aqueous dispersions of nano-sized vesicles. For example, sonication of suspensions of the n-hexylamine-derived iminolipid gave vesicles 50 to 200 nm in diameter that could encapsulate a water-soluble dye. The iminolipids could undergo dynamic exchange with added amines, and the resulting equilibrium constants (Krel) were quantified by 1H NMR spectroscopy. In the absence of lipid self-assembly, in CDCl3, the assayed primary amines gave very similar Krel values. However in D2O the value of Krel generally increased with increasing amine hydrophobicity, consistent with partitioning into a self-assembled bilayer. Amines with aromatic groups showed significantly higher values of Krel in D2O compared to similarly hydrophobic alkylamines, suggesting that π–π interactions favor lipid self-assembly. Given this synergistic relationship, π-rich pyrenyliminolipids were created and used to exfoliate graphite, leading to aqueous dispersions of graphene flakes that were stable over several months.

145 Application of graphene based coating on coronary artery stents

Abstract: Coronary artery disease is the leading cause of death worldwide. Stent implantation is the mainstay approach to revascularise stenosed coronary arteries. Bare metal stents were the first stents designed, but presented a restenosis risk of approximately 20% of patients due to restenosis. Subsequently, drug eluting stents were introduced, which, however, introduced late in stent thrombosis. We propose the use of a graphene based coating onto bare metal stents in an attempt to significantly reduce stent associated complications and promote vessel healing. Graphene is a single layer of carbon atoms arranged in a honeycomb lattice. The unique properties of graphene make it an ideal material to use as an implantable device coating: It has a high surface to volume ratio; it is impermeable and atomically smooth and has been shown to exhibit bio-compatible properties. Graphene based dispersions were prepared by liquid phase exfoliation in water. Investigations to coat bare metal stents were undertaken. Dip, spin and spray coating methods were explored. Raman spectroscopy was measured to identify and characterise the coated material. Raman spectroscopy demonstrated spray coating to result in the most uniform and thin graphene based coating. In addition, human endothelial cell adherence and proliferation on the graphene based coating was studied. Hoechst 33 342 and phalloidin stains were used to image the cells under fluorescence microscopy. This revealed the adherence of human endothelial cells to be unaffected by the graphene based coating. In conclusion, spray coating created the most uniform and thin graphene based coating onto bare metal stents. Human coronary artery endothelial cell adherence occurred on the graphene coated stents. Future work is aimed at studying bio- and haemo- compatibility of graphene based coating and their performance in a porcine stent model.

Water-based 2D-crystal Inks: From formulation engineering to printed devices

Abstract: The electronics industry has been dominated by metals and complementary metal-oxide-semiconductor (CMOS) technology. However, constraints related to materials choice clearly appear in transparent and flexible electronics, heat management and rapid customisation — all of which present challenges to traditional fabrication methods. As a consequence of this need, the field of printable electronics has initially developed after the introduction of conductive polymers, allowing simple, versatile, and low cost techniques, such as inkjet printing, to be used for manufacturing of functional devices [1-2]. The advent of 2-Dimensional (2D) materials [3] show promise in this regard as they can be easily solution processed by using a mass scalable and low cost method, called Liquid-Phase Exfoliation [4]. 2D materials shows great promise for use in flexible electronics because their atomic thickness allows for maximum electrostatic control, optical transparency, sensitivity and mechanical flexibility [5]. In addition, different 2D crystals can be easily combined in one stack, offering unprecedented control on the performance and functionalities of the resulting heterostructure device [3].