Amos Mugweru

Reverse micellar based synthesis of ultrafine MgO nanoparticles (8–10 nm): Characterization and catalytic properties

Anisotropic nanostructures of magnesium oxalate dihydrate were synthesized using cationic surfactant based microemulsion method. The cationic surfactant plays an important role in forming the anisotropic structures. The oxalate nanostructures acts as an excellent precursor for the synthesis of fine magnesium oxide nanoparticles (~10 nm). Both the precursor and the oxide were characterized by using PXRD, IR, surface area and HRTEM. The surface area of these surfactant free oxide nanoparticles was found to be 108 m(2)/g. The catalytic activity of this basic oxide was examined for the Claisen-Schmidt condensation reaction and was found to be comparable to the best reported for the conventionally prepared MgO. Chalcone formation was found to increase with time as observed using gas chromatography-mass spectrometry (GC-MS). The reusability of the catalyst was checked by using the same catalyst twice which showed a reduced percentage (50% compared to first cycle) conversion.

Electrochemical Sensor Array for Glucose Monitoring Fabricated by Rapid Immobilization of Active Glucose Oxidase within Photochemically Polymerized Hydrogels

Background: Currently, monitoring blood glucose levels for diabetic patients is invasive and painful, involving pricking the finger to obtain a blood sample three to four times daily. The need for frequent tests and pain involved with testing leads to poor compliance. In order to raise compliance, we propose to create an implantable electrochemical sensor array that would monitor glucose levels continuously. Methods: Glucose sensor arrays were fabricated on gold electrodes on flexible polyimide sheets by photopolymerization of the biocompatible polymer poly(ethylene glycol) diacrylate (PEG-DA) to develop hydrogels and encapsulate the sensing elements. Using conventional silicon fabrication methods, arrays of five gold microdisk electrodes were fabricated using lift-off photolithography and sputtering techniques. A redox polymer was then attached electrostatically to the electrode, and glucose oxidase was entrapped inside the hydrogel on the array of electrodes by ultraviolet-initiated photopolymerization of PEG-DA. Results: When the array of fabricated sensors was sampled together the elements behaved like one large electrode with peak current equivalent to the sum of individual array elements. The enzyme, glucose oxidase, catalyzed the oxidation of glucose and then exchanged electrons with the redox polymer in the hydrogel. The entrapped glucose oxidase was found to respond linearly to increasing glucose concentrations (0–360 mg/dl), as determined using cyclic voltammetry. Conclusion: The fabricated microarray sensors were individually addressable and showed no cross talk between adjacent array elements as assessed using cyclic voltammetry. We have fabricated an array of glucose sensors on flexible polyimide sheets that exhibits the desired linear response in the biological range.

Manganese based magnetic nanoparticles for heavy metal detection and environmental remediation

The presence of environmental toxins, heavy metals and organic pollutants is a serious environmental issue that has continued to attract much attention from the public as well as the scientific community. In this work we use manganese based magnetic nanoparticles (MNPs) synthesized using a micro-emulsion method and then coated with gold for heavy metal capture and detection. The MNPs were characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Cysteine immobilization onto the gold coated magnetic nano-particles was monitored using Fourier transform infrared (FTIR) spectroscopy. Lead chelation to cysteine on MNPs was monitored using square wave voltammetry. Square wave voltammetry for gold coated MNPs with immobilized cysteine and with chelated lead showed higher current. These MNPs were found to be efficient nano-sorbents for the potential removal of heavy metals from wastewater due to the large surface area.

Electrochemical catalysis of artemisinin on hemoglobin functionalized carbon nanofibers

Artemisinin (ART) is a sesquiterpene lactone and a popular malaria drug used in the Asian subcontinent and some parts of Africa. Understanding the mechanism of action of this drug is important, given recent reports of emergence of resistance of malaria to ARTs. We have investigated biocatalytic reduction of ART on hemoglobin anchored on carbon nanofibers using electrochemistry. We have also investigated the drug interaction with hemoglobin in free solution using liquid chromatography and UV-visible spectroscopy. Using electrochemistry, linear relationships between the catalytic peak current and the ART concentration was observed. The linear range was from 0 to 200 μM and with 0.329 mA mM−1 sensitivity. The calculated apparent Michaelis–Menten constant Km for hemoglobin anchored on carbon nanofibers towards catalysis of ART was 0.093 mM. The analysis of free hemoglobin reacted with ART monitored using UV-visible spectroscopy and liquid chromatography indicated formation of adducts.

Electrochemical and ChromatographicAttributes of Albendazole Drug: ChargeTransfer and Retention Profiles

Methyl [5-propylthio-1H-benzimidazol-2-yl]carbamate (albendazole) is widely used as anthelmintic for the control of gastrointestinal and lung nematodes. The efficacy of this drug is believed to be partly due to the formation of albendazole sulfoxide (ASOX) and oxfendazole (OFZ) in-vivo. Electrochemical oxidation characteristics of albendazole was investigated on a glassy carbon electrode in tetrabutyl ammonium bromide in acetonitrile solution. The non-reversible oxidation of albendazole showed an apparent standard heterogeneous rate constant for electron transfer (kh) 1.39 × 104 S-1 cm2. The value of the electron transfer coefficient (αn) was found to be 0.652. The diffusion coefficient (D) was calculated and found to be 7.12 × 10-8 cm/s. The electrochemical oxidation products at different potentials yielded ASOX and albendazole sulfone (ASON) as determined using chromatography.