Melinda Krebsz

Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors

Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (ID/IG ∼ 0.12), and high conductivity (6.2 × 10(4) S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags.

First Isolation and Spectroscopic Observation of Thiofulminic acid (HCNS)

For the first time: Thiofulminic acid (HCNS), the parent member of the nitrile sulfide family of reactive intermediates and potential interstellar species, was produced and characterized by IR spectroscopy for the first time. HCNS was generated in cryogenic matrices by 254 nm UV irradiation of 1,2,5-thiadiazole (see figure).

Structure, Stability, and Generation of CH3CNS

The unstable acetonitrile N-sulfide molecule CH3CNS has been photolytically generated in inert solid argon matrix from 3,4-dimethyl-1,2,5-thiadiazole by 254-nm UV irradiation, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. The molecule is stable in the matrix to 254-nm UV irradiation, but decomposes to CH3CN and a sulfur atom when broad-band UV irradiation is used. Chemiluminescence due to S2 formation from triplet sulfur atoms was detected on warming the matrix to ∼20–25 K. The ground-state structure and potential uni- and bimolecular reactions of CH3CNS are investigated using B3LYP, CCSD(T), and MR-AQCC quantum-chemical methods. CH3CNS is demonstrated to be stable under isolated conditions at room temperature, i.e. in the dilute gas phase or in an inert solid matrix, but unstable owing to bimolecular reactions, i.e. in the condensed phase.

A matrix isolation and computational study of the [C, N, F, S] isomers

The potential energy surface (PES) of the [C, N, F, S] system was investigated by quantum chemical and experimental methods. Seven minima were located on the ground state PES by density functional and ab initio electronic structure calculations. Four of these isomers, FSCN, FSNC, FCNS and FNCS, have an acyclic structure, while the other three, FC(NS), FS(CN) and FN(SC), form a three-membered fluorine-substituted ring. Out of these seven theoretically predicted isomers, FCNS and FC(NS) were successfully prepared in low-temperature Ar and Kr matrices by photochemical methods. The identification of these species was based on experimental considerations as well as on comparison of their IR spectra to computed anharmonic vibrational frequencies and infrared intensities. The present paper describes not only the first generation of both FCNS and FC(NS) species, but also reports the first time that a substituted CNS ring has been experimentally identified.

Carbon Nanomaterial Based Biosensors for Non-Invasive Detection of Cancer and Disease Biomarkers for Clinical Diagnosis

The early diagnosis of diseases, e.g., Parkinson’s and Alzheimer’s disease, diabetes, and various types of cancer, and monitoring the response of patients to the therapy plays a critical role in clinical treatment; therefore, there is an intensive research for the determination of many clinical analytes. In order to achieve point-of-care sensing in clinical practice, sensitive, selective, cost-effective, simple, reliable, and rapid analytical methods are required. Biosensors have become essential tools in biomarker sensing, in which electrode material and architecture play critical roles in achieving sensitive and stable detection. Carbon nanomaterials in the form of particle/dots, tube/wires, and sheets have recently become indispensable elements of biosensor platforms due to their excellent mechanical, electronic, and optical properties. This review summarizes developments in this lucrative field by presenting major biosensor types and variability of sensor platforms in biomedical applications.

Generation and Spectroscopic Identification of Selenofulminic Acid and Its Methyl and Cyano Derivatives (XCNSe, X=H, CH3, NC)

Evidence for the existence of nitrile selenides, potential 1,3-dipolarophiles in cycloaddition reactions, has been provided by direct spectroscopic methods. The parent nitrile selenide, selenofulminic acid (HCNSe), and its methyl and cyano derivatives have been photolytically generated in an inert solid argon matrix from 1,2,5-selenadiazoles by 280, 254, and 313 nm UV irradiation, respectively, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. Ground-state geometries have been obtained from quantum-chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Nitrile selenides are predicted to be linear with a relatively weak N-Se bond.

Generation and Spectroscopic Identification of ClCNS, ClNCS and NCCNS

The photolysis of four chloro-substituted thiadiazoles (3,4-dichloro-, 3-chloro- and 3-chloro-4-fluoro-1,2,5-thiadiazole; 3,5-dichloro-1,2,4-thiadiazole) and 3,4-dicyano-1,2,5-thiadiazole was investigated in inert solid-argon matrices at cryogenic temperatures by means of UV irradiation at selected wavelengths of 254 and 280 nm. The photolysis products were identified by mid-IR and UV spectroscopy. Evidence for the existence of three novel pseudohalides, namely, chloronitrile sulfide (ClCNS), chlorine isothiocyanate (ClNCS) and cyanogen N-sulfide (NCCNS), was provided by direct spectroscopic methods supported by quantum chemical calculations. Ground-state geometries, vibrational frequencies, IR intensities, and UV excitation energies of ClCNS, ClNCS and NCCNS were obtained from calculations using the B3LYP, CCSD(T) and SAC-CI methods and the aug-cc-pV(T+d)Z basis set.

Copper nanoparticles grafted on carbon microspheres as novel heterogeneous catalysts and their application for the reduction of nitrophenol and one-pot multicomponent synthesis of hexahydroquinolines

Novel carbon microsphere-supported metallic copper nanoparticles (Cu-NP/C) were synthesized using a low-cost and facile method based on carbonising a styrene-based, chelate-forming cation exchange resin loaded with Cu2+ ions. The metal–organic framework served as both copper and carbon source. Cu-NP/C microspheres were characterized by XRD, Raman, SEM, TGA, EDAX, and BET surface area analyser and were employed as heterogeneous catalysts for the reduction of 4-nitrophenol to 4-aminophenol by NaBH4 and for the synthesis of medicinally significant hexahydroquinoline derivatives based on the one-pot, multi-component reaction of aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate. The sustainable and cheap starting material, the relatively easy synthetic procedure, the catalytic efficiency, and the easy separation and reusability of Cu-NP/C microspheres open the door for their wide-scale application.

Biosensors for Non-Invasive Detection of Celiac Disease Biomarkers in Body Fluids

Celiac disease is a chronic gluten-initiated autoimmune disorder that predominantly damages the mucosa of the small intestine in genetically-susceptible individuals. It affects a large and increasing number of the world’s population. The diagnosis of this disease and monitoring the response of patients to the therapy, which is currently a life-long gluten-free diet, require the application of reliable, rapid, sensitive, selective, simple, and cost-effective analytical tools. Celiac disease biomarker detection in full blood, serum, or plasma offers a non-invasive way to do this and is well-suited to being the first step of diagnosis. Biosensors provide a novel and alternative way to perform conventional techniques in biomarker sensing, in which electrode material and architecture play important roles in achieving sensitive, selective, and stable detection. There are many opportunities to build and modify biosensor platforms using various materials and detection methods, and the aim of the present review is to summarize developments in this field.

Development of Vapor/Gas Sensors From Biopolymer Composites

Abstract Biopolymers, due to their abundance, biocompatibility, and unique properties, are very promising materials for highly selective and sensitive gas and vapor sensors. New research projects are targeting the development of highly specific biopolymer composite receptors and new transducer platforms for developing electrical noses (e-noses) for wide range applications in industry, environmental monitoring, disease monitoring, defense, and public safety. In recent years, gas sensors containing biopolymer films, self-assembled monolayers of biopolymers, carbon nanoparticle–doped biopolymer films, and biopolymers hybridized with conducting organic polymers, as well as carbon nanotubes modified with biopolymers were fabricated and tested for various gases and vapors. Sensitivity, selectivity, response time, and reversibility of biopolymer-based sensors, in general, are respectable, and thus biopolymer-based sensors are challenging traditional inorganic and organic sensors. In this review, the current development and future aspects of the new field of biopolymer gas and vapor sensors are presented.