Monitoring magnesium degradation using microdialysis and fabric-based biosensors

This paper describes the development of a monitoring system capable of detecting the concentration of magnesium ions (Mg2+) released during the degradation of magnesium implants. The system consists of a microdialysis probe that samples fluid adjacent to the implant and a catalytic biosensor specific to Mg2+ ions. The biosensor was fabricated on a cotton fabric platform, in which a mixture of glycerol kinase and glycerol-3-phosphate oxidase enzymes was immobilized on the fabric device via a simple matrix entrapment technique of the cotton fibers. Pure magnesium was used as the implant material. Subsequently, the concentration of ions released from the degradation of the magnesium specimen in Ringer’s solution was evaluated using cyclic voltammetry technique. The device demonstrated a pseudo-linear response from 0.005 to 0.1 mmol L−1 with a slope of 67.48 μA mmol−1 L. Detectable interfering species were lesser than 1% indicating a high selectivity of the fabric device. Furthermore, the device requires only 3 μL of fluid sample to complete the measurement compared to spectroscopic method (±50 μL), hence providing a higher temporal resolution and reduced sampling time. The system could potentially provide a real time assessment of the degradation behavior, a new studied aspect in biodegradable metals research

An investigation of reaction parameters for carbon dioxide utilisation

Carbon dioxide emissions per year have risen exponentially. It is widely known the contribution of CO2 to global warming phenomena, so storage/utilisation of carbon dioxide has become a topical issue and an emerging research area. Despite the fact that utilization of CO2 waste would not solve the problem of the huge quantities going to the atmosphere every year as only less than 1% of it could be reused for the industry, recycled carbon dioxide presents itself as a possible cheap and accessible chemical feedstock. The challenge on recycling CO2 is to minimize energy and cost efficiency of any suitable reaction. On previous investigations the electrochemical synthesis of 5-membered cyclic carbonate from epoxides was accomplished under mild conditions and optimized (1 atm CO2 pressure, 60 mA constant current and 50 °C heating). In order to understand the mechanism of this electrochemical process a deep investigation on the variables of the synthesis of cyclic carbonates was carried out and is presented in this thesis. The variables studied include electrochemical system conditions (application of current through Cu/Mg electrodes, electrodes connected on a closed circuit system with no current, an open circuit system where electrodes were there was no connection between them, and reactions without electrodes), temperature of reaction, solvent screening, catalysts, epoxide substituents, concentration of species and ratio of reactants. As a result of the variables optimization, a new, cheap, simple and relatively fast method (5 to 24 hours of reaction time) for cyclic carboxylation of epoxides with CO2 at atmospheric pressure in acetonitrile in the presence of ammonium salt (TBAI) at mild temperatures (50 - 75 °C) has been developed and improved. The concentration of the reactants, especially of the epoxide, was found to be the most important factor on the success of the reaction. The new reaction conditions also allow converting epoxides to carbonates without the help of any cocatalyst or electrochemical system obtaining excellent yields (50-100%) with the important saving on cost and energy of co-catalyst synthesis and recovery. Chlorostyrene oxide (1 M) reacted almost completely (94%) after 24 hours with TBAI (1 M), in 1 mL of acetonitrile at 75 °C and 1 atm pressure of CO2. Epoxide carboxylation under neat conditions was feasible, producing 44% of chlorostyrene carbonate from chlorostyrene oxide in the presence of TBAI at 75 °C and 1 atm pressure of CO2

A Miniaturized Enzymatic Biosensor for Detection of Sensory-Evoked D-serine Release in the Brain

D-serine has been implicated as a brain messenger with central roles in neural signaling and plasticity. Disrupted levels of D-serine in the brain have been associated with neurological disorders, including schizophrenia, depression and Alzheimer's disease. Electrochemical biosensors are attractive tools for measuring real-time in vivo D-serine concentration changes. Current biosensors suffer from relatively large sizes (≥25 μm) making localized cellular measurements challenging, especially for single cell studies. In this work, a robust methodology for the fabrication of a reproducible miniaturized 10 μm D-serine detecting amperometric biosensor was developed. The miniature biosensor incorporated yeast D-amino acid oxidase immobilized on a poly-meta-phenylenediamine modified 10 μm Pt disk microelectrode. The biosensor offered a limit of detection of 0.361 μM (RSD < 10%) with high sensitivity (283 μA cm-2 mM-1, R2 = 0.983). The biosensor was stable for over four hours of continuous use, demonstrated a storage stability of four days and high analyte selectivity. Biosensor selectivity was validated with LC-MS and interferences with yeast D-amino acid oxidase were evaluated using drugs believed to stimulate D-serine release. Ex vivo D-serine measurements were made from Xenopus laevis tadpole brains, demonstrating the utility of the biosensors for measurements on living tissue. We observed that D-serine levels in the brain fluctuate with sensory experience. The biosensors were also used in vivo successfully. Taken together, this study addresses factors for successful and reproducible miniature biosensor fabrication for measuring D-serine in biological samples, for pharmacological evaluation, and for designing point of care devices

Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement

Ion-sensitive membrane-based sensors and ionic processes in bio-membranes are the focus of this book. The chapters are carefully chosen to characterize essential research trends, applications, and perspectives. They include solid contact ion-selective and reference electrodes and their electroanalytical behavior in zero and nonzero-current modes, planar and miniaturized multielectrode platforms, ion monitoring in extreme sports, and transmembrane transport through living endothelial cells to find the volume. This book is crowned by the consideration of a yet unexplored ion status in a mitochondrial matri

Towards stable and efficient electrolytes for room-temperature rechargeable calcium batteries

Rechargeable calcium (Ca) batteries have the prospect of highenergy and low-cost. However, the development of Ca batteries is hindered due to the lack of efficient electrolytes. Herein, we report novel calcium tetrakis(hexafluoroisopropyloxy)borate Ca[B(hfip)₄]₂ based electrolytes exhibiting reversible Ca deposition at room temperature, a high oxidative stability up to 4.5 V and high ionic conductivity >8 mS cm¯¹. This finding opens a new approach towards room-temperature rechargeable calcium batteries

AN ION SELECTIVE MICROGRIPPER SENSOR DEVICE

This thesis presents the design, fabrication, characterisation and testing of a chemically modified electrothermally actuated microgripper. The chemical modification involves the integration of a potentiometric ion selective electrode (ISE) onto a bare electrode fabricated within the tip of the microgripper. This microgripper sensor device is intended for use in the application of detecting, in real time, the movement of key ions that are involved in intercellular communication from a mechanically stressed cell. An optimised fabrication route for the specifically designed microgrippers, which have tip dimensions of 10 – 60 µm, is described in detail. The fabrication route delivers a high yield (95%) of operational unmodified devices. An 1800 ± 20 µm2 bare gold electrode that is fabricated at the tip of the microgripper is modified into an all solid state ISE that uses PEDOT as the ion-to-electron solid contact. Suitable ionophores that selectively detect K+, Na+ and Ca2+ are used to fabricate potassium, sodium and calcium ion selective microgripper sensor devices. The quality control and testing characteristics that follow the guidelines defined by IUPAC are performed to ascertain the sensitivity, selectivity and stability of the microgripper sensor devices. Good selectivity is achieved, with limits of detection of 2.4 x 10-4 M, 1.8 x 10-4 M and 2.0 x 10-5 M for the K+, Na+ and Ca2+ devices respectively. Proof of concept experiments of the real life testing of the K+ ISE device used to mechanically stress mouse oocytes gave preliminary measurements that indicate that stress signalling occurs via a switch on mechanism, and that there is a small increase in K+ concentration as applied stress increases. Due to the high systematic error within the calibration process the magnitude of this concentration increase is unknown. The Na+ and Ca2+ ISE devices suffer from interference and sensitivity restrictions respectively so a signal response vs. applied cell stress relationship of these ions is currently unobtainable

Pectin modified metal nanoparticles and their application in property modification of biosensors

Pectin is a structural anionic heteropolysaccharide and abundantly found in the cell wall of terrestrial trees and plants. It exhibits several advantageous properties such as non-toxicity, cheap, biodegradable, biocompatible, abundant, flexible, etc. Functional groups like carboxylic acid and hydroxyl make pectin suitable to be covalently bonded with other biomolecules and proteins. Based on these properties, pectin is being extensively employed to encapsulate/coat metal nanoparticles (MNPs) to inhibit their aggregation and enhancing the suitability of MNPs for a wide range of applications in healthcare like drug delivery, antimicrobial activity, antioxidant etc. Another important application of pectin is to enhance the electrochemical performances of sensors in which electrode materials are modified with pectin, which immobilizes the enzyme without disturbing the basic electron transfer properties of the electrode. Thus pectin is found to have great potential for developments in future in various fields like sensing, drug delivery etc. This review covers the application of pectin for MNPs stabilization and electrochemical sensors to improve their properties. The review also emphasizes synthetic strategies and electrochemical analysis of analytes. This review will provide a comprehensive overview of pectin’s applicability and can help to design novel and efficient MNPs and electrochemical sensors for a wide range of applications

Chemical Investigation of Leaching and Electrochemical Behaviour of Sensor-based Pre-concentrated Copper Ores with Alkaline Lixiviant

OKAbstract While the production of copper metal from primary ores is still increasing, the gradual depletion of high-grade ores implies that the recovery of the metal from low-grade ores is presenting a challenge. A major problem associated with processing of low-grade copper ores can be their high calcite content and concentration of other metals such as Fe, Mn, Co, As, Pb, and Ni. These other metals make the processing of such ores expensive due to the high cost of the leaching chemicals. Therefore, in this study a novel, integrated copper processing method is developed to enhance the economic extraction of copper from such ores. This research investigated the chemical leaching behaviour of porphyry copper ore samples from Chile, South America. Ores were pre-concentrated and classified with near infrared sensing into product, middling and waste fractions. Mineralogical analysis of the ore was conducted using QEMSCAN®, XRD and NIR. The elemental investigation of the ore was carried out using PXRF, ICP-MS and SEM. Analyses revealed that the major copper-bearing mineral is chrysocolla and that the ore is composed mainly of silicate, oxide and carbonate gangue. Calcite in the ore is considered problematic due to acid consumption. In terms of abundance of gangue in the classified ore the order is waste > middling and product. A systematic comparison of the complexometric behaviour of the ore was investigated with Na2EDTA reagent while the leaching behaviour of the classified ore was investigated in NH4Cl and H2C2O4 lixiviants. The influence of process variables such as lixiviant concentrations, particle sizes, solid-to-liquid ratio, temperature, time and stirring speed on the behaviour of the classified ore were investigated. The rate of Cu dissolution and formation of Cu-EDTA complex in Na2EDTA was higher in the product than the middling while that of the waste was found to be insignificant at 0.01 M, even when the concentration of the complexing agent was increased from 0.01 M to 0.05 M. The rate of Cu-EDTA complex formation was found to increase with decreasing particle sizes and solid-to-liquid ratio across the ore categories. Ammonium chloride leaching of the product and middling revealed contrasting behaviour. The rate of Cu extraction was found to increase significantly from 21.5 % to 75.0 % and 27.3 % to 89.0 % when the temperature was increased from 40 ˚C to 90 ˚C, respectively. On increasing the concentration of NH4Cl from 0.5 M to 5 M, the extraction of Cu was found to increase from 20.0 % to 65.0 % and 26.5% to 83.3 %, respectively. It was found that the leaching yield of Cu increased substantially when the particle size was decreased from –125+90 μm to –90+63 μm and –63+45 μm and with decreasing solid-to-liquid ratio (middling and product), respectively. A steady decrease in Cu extraction was obtained when the stirring speed was increased from 300 rpm to 800 rpm. Similarly, the effectiveness of the leaching process was investigated over an extended time period from 2 h to 4 h with an NH4Cl concentration range of 0.55 M to 1.65 M, a temperature of 70 ˚C to 90 ˚C, and at a constant stirring speed of 300 rpm, particle size fraction of -64+45 μm and a solid to liquid volume of 6 g/ 250 mL. It was found that Cu extraction was enhanced by about 90 % during the experiment. The estimated activation energy of the leaching process was characterized using the shrinking core model under the experimental conditions. It was found to range between 45 and 71 KJ/mol in the first and second batch experiments, which is indicative of a chemically controlled leach process. XRD and ICP-MS characterization of mineralogical and chemical composition of residues suggested that the NH4Cl lixiviant leaching is selective for Cu. Examination of leachate with ICP-MS for co-extraction of Mn, Co, Ni and Zn indicated insignificant solubilisation of the metals during leaching. Comparison of Cu extraction in NH4Cl and H2C2O4 under the same experimental conditions revealed that NH4Cl is a better extractant than H2C2O4. Furthermore, the electrodeposition of Cu metal was studied with ore leachate containing Cu(NH3)42+ complexes and with Cu(NH3)4SO4 synthetic electrolyte. Cyclic voltammetric measurements were conducted across a range of cathodic potentials from 0.8 V to – 1.0 V for selected scan rates of 20, 30, 50, 100 and 200 mV/s. Chemical reduction and electrodeposition of Cu from the complexes was found to proceed via two reversible electrochemical processes, each involving the transfer of a single electron. Cu(NH3)42+ complexes are first reduced to Cu(NH3)2+, which is in turn reduced to metallic Cu. The result is compared with the behaviour of synthetic Cu(NH3)4SO4 electrolyte. It was observed that the reduction of Cu(NH3)4SO4 to metallic Cu proceeds as two sequential, single electron transfer processes. The Cu/Cu(NH3)42+ redox reaction was observed to be fast compared to Cu/Cu2+ redox reaction in the Cu(NH3)4SO4 solution. Investigation of the electrochemical kinetics shows that the cathodic peak current varied linearly with the square root of the scan rate, which is indicative of the Cu(NH3)2+ and Cu(NH3)4SO4 reduction to Cu proceeding through a diffusion-controlled process. Assessment of the effect of calcite for leaching of copper from classified ore fractions indicated the potential of NH4Cl lixiviant for the leaching application. Three processing routes to handle the ore fractions on the basis of variation in calcite, gangue and copper content are proposed.Nigerian Tertiary Education Trust Fund (TETFund

INVESTIGATION OF CHEMICAL DIFFERENCES IN MEDICATIONS OBTAINED FROM DIVERSE SOURCES USING NOVEL SPECTROSCOPIC AND STATISTIC APPROACHES

Generic medications are those medicines manufactured by a pharmaceutical company without a license from the company that has first invented and patented the same drug, when the related patent and other exclusivity rights have expired. Only studies of bioequivalence are requested as requirements to introduce a new generic medication in clinics, making easier and financially attractive for many pharmaceutical companies to participate in this typology of market. Organised criminality is strongly attracted by this market both for the high profitability, and for the high similarity to the production and trafficking of illegal controlled substances associated to the extreme difficulties faced by the law enforcement authorities in effectively investigating the online market, because of its anonymity. A significant paradigm continuously frequented in pharmacology is the confliction between views on generic medications that can be used interchangeably with the original medicines. Several clinical studies conducted in certain medical areas have shown as the generic medications present an overlapping therapeutic equivalence to the original ones. On the contrary, for certain other generics, both pharmacokinetics and pharmacodynamics issue have been reported. Also, in some cases issues on the stability of generics have been raised. Despite the numerous research articles and reviews published on the matter of clinical equivalence among generic and original medications, no study to the scientific community has been presented on an analytical evaluation of the chemical composition of the different generic drugs that could shed some lights on the reason of the different clinical performances reported. The main aim of this research was to develop a non-destructive quick qualitative analytical methodology to be able to discriminate differences in the chemical composition from generic medicines that have been reported not presenting similar therapeutic equivalence in clinical comparison studies, obtained from authorised pharmacies and non-authorised online sellers. From the cardio-vascular area, digoxin (with the related cardiac glycosides digitoxin and digoxigenin) and amlodipine (in its different salts maleate, mesylate and besylate used in therapies). In the gastroenterology area, omeprazole both in its racemic and isomeric forms, have been selected as samples to be analysed. In the antihistamine area, cetirizine, in its racemic and isomeric forms, equally for the same reasons as before, have been considered. As starting analytical approaches, voltammetry, FT-IR, Raman spectroscopies and NMR have been considered and a statistical data analysis approach of the analytical data obtained based on multivariate analysis such as principal component analysis, cross validation, correlation scatter plots and factor loadings has been implemented. This work has matched the aims initially set, generating novel methods of analysis to investigate differences in the chemical composition within different groups of generic medications. This study has led to the creation and interpretation of new knowledge, through a systematic acquisition and understanding of a substantial body of scientific literature and through original research, and adjusting the project design in the light of unforeseen problems, conceptualizing, designing and implementing the research project for the generation of novel knowledge