An overview of recent applications of reduced graphene oxide as a basis of electroanalytical sensing platforms

© 2017 The Authors The academic literature using graphene within the field of electrochemistry is substantial. Graphene can be fabricated via a plethora of routes with each having its own unique merits (e.g. cost, fabrication time, quality and scale) and reduced graphene oxide (rGO) is more often the material of choice for electrochemical sensors and associated applications due to its ease of fabrication and ability to be mass produced on the kilogram scale. This review overviews pertinent developments in the use of rGO as the basis of electroanalytical sensors (2016–2017); guidelines for the progression of this field are also given

Holographic Point-of-Care Diagnostic Devices

Developing non-invasive and accurate diagnostics that are easily manufactured, robust and reusable will provide monitoring of high-risk individuals in any clinical or point-of-care environment, particularly in the developing world. There is currently no rapid, low-cost and generic sensor fabrication technique capable of producing narrow-band, uniform, reversible colorimetric readouts with a high-tuneability range. This thesis aims to present a theoretical and experimental basis for the rapid fabrication, optimisation and testing of holographic sensors for the quantification of pH, organic solvents, metal cations, and glucose in solutions. The sensing mechanism was computationally modelled to optimise its optical characteristics and predict the readouts. A single pulse of a laser (6 ns, 532 nm, 350 mJ) in holographic “Denisyuk” reflection mode allowed rapid production of sensors through silver-halide chemistry, in situ particle size reduction and photopolymerisation. The fabricated sensors consisted of off-axis Bragg diffraction gratings of ordered silver nanoparticles and localised refractive index changes in poly(2-hydroxyethyl methacrylate) and polyacrylamide films. The sensors exhibited reversible Bragg peak shifts, and diffracted the spectrum of narrow-band light over the wavelength range λpeak ≈ 500-1100 nm. The application of the holographic sensors was demonstrated by sensing pH in artificial urine over the physiological range (4.5-9.0), with a sensitivity of 48 nm/pH unit between pH 5.0 and 6.0. For sensing metal cations, a porphyrin derivative was synthesised to act as the crosslinker, the light absorbing material, the component of a diffraction grating, as well as the cation chelating agent. The sensor allowed reversible quantification of Cu2+ and Fe2+ ions (50 mM - 1 M) with a response time within 50 s. Clinical trials of a glucose sensor in the urine samples of diabetic patients demonstrated that the glucose sensor has an improved performance compared to a commercial high-throughput urinalysis device. The experimental sensitivity of the glucose sensor exhibited a limit of detection of 90 µM, and permitted diagnosis of glucosuria up to 350 mM. The sensor response was achieved within 5 min and the sensor could be reused about 400 times without compromising its accuracy. Holographic sensors were also tested in flake form, and integrated with paper-iron oxide composites, dyed filter and chromatography papers, and nitrocellulose-based test strips. Finally, a generic smartphone application was developed and tested to quantify colorimetric tests for both Android and iOS operating systems. The developed sensing platform and the smartphone application have implications for the development of low-cost, reusable and equipment-free point-of-care diagnostic devices

Devices and systems based on two dimensional MoO3 and MoS2

Materials that are composed of atoms which are covalently bonded in two dimensional (2D) planar spaces are considered quasi 2D materials. Graphene is an excellent example of a 2D structure and of great interest due to its enhanced carrier mobilities. The enhancement in carrier mobility is due to the emergence of near massless fermions in 2D graphene. Such large carrier mobilities are of great value for the development of future transistors, as the current technologies for the fabrication of nanostructured silicon transistors are fast exceeding their limits in reducung size and enhancing their performance.The aim of this Ph.D. research is to synthesize and characterize the properties of 2D MoO 3 and MoS 2 , in order to realize 2D electronic devices with high carrier mobilities and understand the behaviour of these 2D materials upon small ion intercalation. The author of this thesis thoroughly reviewed the fundamental properties, as well as methods of synthesis and properties of layered MT&DCs. Based on the review, the author recognized some of the niche areas to be further investigated regarding 2D MoS2. The author identified the lack of a simple and efficient process for the synthesis of layered MoS 2 . Additionally, the author identified 2D molybdenum trioxide (MoO 3 ) as the core material suitable for the development of a new family of 2D electronic devices and systems. MoO 3 is an intrinsically high dielectric material with tuneable electronic properties. This tunability can be achieved via facile ion intercalation. In order to realize the aforementioned goals and to create new knowledge, the author implemented his research work in three distinct stages. The first stage involved realizing 2D MoS 2 flakes for the purpose of investigating the structural effects of ion intercalation in comparison to its bulk counterpart. The author developed a simple and effective method of synthesis involving the simultaneous co-evaporation of MoO 3 powder together with sulphur. The MoS 2 was characterized to be high purity layered nanostructures. Subsequently, the author realized 2D MoS 2 via mechanical exfoliation of the as obtained material. The author the conducted electrochemical lithium ion exposure studies and investigated the effects using Raman spectroscopy presenting a new insight regarding the vibrational properties of such systems. In the second stage, the author synthesized layered α-MoO 3 crystals by the thermal evaporation of MoO 3 powder. 2D MoO 3 layers were realized via micromechanical exfoliation of as obtained crystals. The author demonstrated various approaches of H + intercalation and partial reduction of MoO 3 , for the purpose of reducing the bandgap to be viable for FET applications. The author then developed FETs based on such 2D MoO 3 flakes with enhanced carrier mobilities exceeding 1100 cm 2 V –1 s –1 . Such mobility was significantly larger than the best of those reported for the 2D MoS 2 based FETs and en par with the best mobilities offered by silicon technology. Overall, the author strongly believes that the objectives achieved in this Ph.D. research work, have contributed significantly to the advancement of 2D electronic devices and systems as well as created exciting new knowledge

Pharmaceutical Analysis of Polyamines and Aminoglycosides

Methods for polyamine derivatization with a panel of extrinsic fluorophores followed by HPLC with fluorescence and UV absorption detection have been developed. Four fluorophores were examined using polyamines and aminoglycosides. o-Phthalaldehyde (OPA) and fluorescamine are selective fluorophores that only react with primary amines; 9- fluorenylmethyl chloroformate (FMOC Cl) and dansyl chloride react with both primary and secondary amines. Reaction and HPLC conditions were optimized with each of the above fluorophores using a series of model mono- and diamines and then applied to natural and semi-synthetic polyamines. The amines that have been investigated are natural di- and polyamines: putrescine, cadaverine, spermidine, spermine, thermospermine, aminoglycosides: kanamycin, paramomycin, neomycin, and synthetic polyamine conjugates e.g. N⁴,N⁹-dioleoylspermine, N¹-cholesteryl spermine carbamate. The resultant derivatives were confirmed by off-line high resolution electrospray ionization mass spectrometry (HR ESI MS). The results show that the synthesis of polyamine derivatives in quantitative yield depends on the time of reaction, the temperature and the ratio of fluorophore reagent. Linearity of derivatization was calculated and regression coefficients ranged from 0.968 to 0.999 with good reproducibility. HR ESI MS analysis of the reaction products demonstrated complete derivatization of both primary and secondary amino groups with dansyl and FMOC fluorescence derivatives and of primary amine groups for OPA and fluorescamine derivatives. Under the ionization conditions used the dansyl derivatives showed, in addition to monovalent ions [M+H]⁺, divalent cations [M+2H]²⁺ because this chromophore contains a basic amine that can be easily protonated. FMOC derivatives gave prominent [M+Na]⁺ ions. The OPA derivatization reaction is rapid, but the products have poor stability. The derivatization with fluorescamine gave multiple products with glucosamine due to the presence of a chiral centre in the fluorophore. The relative quantum yields of the polyaminefluorophore derivatives were examined to determine the effect of intramolecular fluorescence quenching. Dansylation is the fluorescent derivatization method of choice.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

State-of-the-art materials science in Belgium 2017

This book is a collection of both review and original research papers which appeared in a Special Issue of the open access journal, Materials, “State-of-the-Art Materials Science in Belgium 2017”. It covers a wide range of selected material topics, currently under investigation at universities throughout Belgium. As a country, Belgium has hardly any physical resources which can be exploited in materials research and development or industry. However, the resource drawback is compensated by focussing on highly technological fields of research, not requiring vast amounts of raw material. This ‘high-tech’ approach includes the development of new analytical methods for the characterization of materials, research into new advanced functional materials, as well as defining new industrial processes for existing materials. As such, the book presents a contemporary view on materials research activities in Belgium