Stephen Mailu - Academia.edu (original) (raw)
Papers by Stephen Mailu
Ethambutol (2S, 2′S)-2, 2′-(ethane-1, 2-diyldiimino) dibutan-1-ol) is a first-line antitubercular... more Ethambutol (2S, 2′S)-2, 2′-(ethane-1, 2-diyldiimino) dibutan-1-ol) is a first-line antitubercular drug effective against actively growing Mycobacterium tuberculosis. Resistance of the mycobacterium to ethambutol among tuberculosis (TB) patients results from inadequate or inappropriate dosing of treatment or using low quality medication. It is therefore necessary to develop reliable methods for determining the ethambutol metabolic profile of patients at point of care for proper dosing. Herein an efficient ethambutol bioelectrochemical nanosensor device is illustrated. It consists of cytochrome P450-2E1 (CYP2E1) immobilised on electroactive nanocomposites of poly (8-anilino-1-napthalene sulphonic acid) (PANSA) and silver nanoparticles (AgNPs) stabilized in polyvinylpyrrolidone (PVP). The performance of the ethambutol nanobiosensor (Au / PANSA/AgNPs /CYP2E1) was interrogated amperometrically. The biosensor gave a dynamic linear range of 2-12 µM, a sensitivity of 1.125µA/µM, detection l...
Conducting polymers have elicited much interest among researchers because of their reasonably goo... more Conducting polymers have elicited much interest among researchers because of their reasonably good conductivity, stability, ease of preparation, affordability and redox properties compared to other organic compounds. In particular, the electronic and electrochemical properties of conducting polymers have made them find applications in photovoltaic cells, organic light emitting diode and sensors. Among the conducting polymers, polyaniline has received much attention and intensive research work has been performed with the polymer in its native state or functionalized form. This is mainly due to the fact that polyaniline and its derivatives or composites or co-polymers with other materials are easy to synthesise chemically or electrochemically by oxidative polymerisation. The mechanism for the synthesis of polyaniline and its electronic properties are presented in this short review.
Sensors, 2014
An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-mul... more An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L −1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng −1 and 0.46 pg L −1 , respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg −1 and the
Sensors, 2011
Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010.... more Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010. [...]
Electrochimica Acta, 2014
Electrochimica Acta, 2011
The redox properties of electro-polymerized polypyrrole (Ppy) doped with different surfactants we... more The redox properties of electro-polymerized polypyrrole (Ppy) doped with different surfactants were studied in acid medium. It was found out that the addition of different surfactants affect the redox properties as evidenced by diffusion coefficients and rate constants calculated from experimental data obtained from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three different surfactants were incorporated into polypyrrole matrix to form homogeneous composites i.e. anionic surfactant polyvinylsulphonic acid (PVSA) as well as non-ionic surfactants (polyethylene glycol p-(1,1,3,3tetramethylbutyl)-phenyl ether (Triton-X 100) and polyoxyethylene (20) sorbitan monolaurate (Tween 20). CV and EIS experiments were carried in the presence of the redox probe K 3 [Fe(CN) 6 ]. Diffusion coefficient was interpreted as a measure of electron movement within the composite polymer structure and rate constant was interpreted as a measure of the rate of oxidation and reduction of the redox probe. The highest value for diffusion coefficient and rate constant was obtained for Ppy/PVSA as 8.16 × 10 −12 cm 2 s −1 and 1.05 × 10 −5 cm s −1 respectively. The values obtained by CV and EIS were in good agreement.
Int. J. Electrochem …, 2011
Biocompatible and water soluble 3-mercaptopropionic acid capped gallium selenide nanocrystals wer... more Biocompatible and water soluble 3-mercaptopropionic acid capped gallium selenide nanocrystals were synthesized from hydrated gallium (III) perchlorate and selenide ions. The nanocrystals were nonfluorescent but showed a sharp UV-vis absorption maximum at 260 nm. Transmission electron micrographs showed the formation of high quality non-aggregated particles with an average diameter of 65 nm. Gold electrode modified with the capped nanocrystals was used as a platform for impedimetric genosensing using NH 2-5′-CCCACCGGTCCTTCATGTTC-3′ (probe) and 5′-GAACATGAAGGA CCGGTGGG-3′ (target) oligonucleotide sequences. The target oliginucleotide sequence is a component of 5-enolpyruvylshikimate-3-phosphate synthase, a common vector gene in glyphosate resistant transgenic plants. The impedimetric genosensor exhibited high sensitivity towards the target DNA (sensitivity = 11.61 Ω/nM) with a detection limit of 0.66 nM (3s, n = 8). The genosensor was able to discriminate between complementary, non-complementary and 3-base mismatched target sequences and maintained 87 % of its response towards the target DNA after one month.
Electrochimica Acta, 2014
Impedimetry and microscopy of electrosynthetic poly(propylene imine)-copolypyrrole conducting den... more Impedimetry and microscopy of electrosynthetic poly(propylene imine)-copolypyrrole conducting dendrimeric star copolymers, Electrochimica Acta (2014),
Sensors, 2010
A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy... more A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO 3 and HAuCl 4 using C 6 H 5 O 7 Na 3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20-50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10 −6 to 3.56 × 10 −4 M with a detection limit of 1.69 × 10 −7 M. The proposed method was simple, less time consuming and showed a high sensitivity.
Electrochimica Acta, 2014
Nanostructured poly(4-styrene sulphonic acid) and tantalum (IV) oxide-doped polyaniline nanocompo... more Nanostructured poly(4-styrene sulphonic acid) and tantalum (IV) oxide-doped polyaniline nanocompos-ite were synthesised and their electro-conductive properties were determined. The oxide was synthesizedusing a modified sol-gel method and then dispersed in acidic media through sonication and entrappedin-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped withpoly(4-styrene sulphonic acid). The oxides and novel polymeric nanocomposite were characterised withTEM, SEM, EDX, XRD, FTIR, UVvisible to ascertain elemental and phase composition, successful polymer-ization, doping, morphology and entrapment of the metal oxide nanoparticles. The electro-conductivityof the nanomaterial was interrogated using scanning electrochemical microscopy (SECM) and cyclicvoltammetry (CV). The material was then anchored on activated graphitic carbon and used in the designof an asymmetric supercapacitor cell using 6 M KOH aqueous electrolyte. Characteristically high specific capacitance values of 318.4 F/g with a corresponding energy and power densities of 1.57 kWh/kgand 0.435 kW/kg, respectively, were demonstrated. The cell also showed high coulombic efficiency of94.9% with a long cycle life and good cycle stability making the nanomaterial suitable for constructingsupercapacitor cell electrodes.
Electrochimica Acta, 2014
ABSTRACT
Ethambutol (2S, 2′S)-2, 2′-(ethane-1, 2-diyldiimino) dibutan-1-ol) is a first-line antitubercular... more Ethambutol (2S, 2′S)-2, 2′-(ethane-1, 2-diyldiimino) dibutan-1-ol) is a first-line antitubercular drug effective against actively growing Mycobacterium tuberculosis. Resistance of the mycobacterium to ethambutol among tuberculosis (TB) patients results from inadequate or inappropriate dosing of treatment or using low quality medication. It is therefore necessary to develop reliable methods for determining the ethambutol metabolic profile of patients at point of care for proper dosing. Herein an efficient ethambutol bioelectrochemical nanosensor device is illustrated. It consists of cytochrome P450-2E1 (CYP2E1) immobilised on electroactive nanocomposites of poly (8-anilino-1-napthalene sulphonic acid) (PANSA) and silver nanoparticles (AgNPs) stabilized in polyvinylpyrrolidone (PVP). The performance of the ethambutol nanobiosensor (Au / PANSA/AgNPs /CYP2E1) was interrogated amperometrically. The biosensor gave a dynamic linear range of 2-12 µM, a sensitivity of 1.125µA/µM, detection l...
Conducting polymers have elicited much interest among researchers because of their reasonably goo... more Conducting polymers have elicited much interest among researchers because of their reasonably good conductivity, stability, ease of preparation, affordability and redox properties compared to other organic compounds. In particular, the electronic and electrochemical properties of conducting polymers have made them find applications in photovoltaic cells, organic light emitting diode and sensors. Among the conducting polymers, polyaniline has received much attention and intensive research work has been performed with the polymer in its native state or functionalized form. This is mainly due to the fact that polyaniline and its derivatives or composites or co-polymers with other materials are easy to synthesise chemically or electrochemically by oxidative polymerisation. The mechanism for the synthesis of polyaniline and its electronic properties are presented in this short review.
Sensors, 2014
An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-mul... more An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L −1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng −1 and 0.46 pg L −1 , respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg −1 and the
Sensors, 2011
Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010.... more Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010. [...]
Electrochimica Acta, 2014
Electrochimica Acta, 2011
The redox properties of electro-polymerized polypyrrole (Ppy) doped with different surfactants we... more The redox properties of electro-polymerized polypyrrole (Ppy) doped with different surfactants were studied in acid medium. It was found out that the addition of different surfactants affect the redox properties as evidenced by diffusion coefficients and rate constants calculated from experimental data obtained from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three different surfactants were incorporated into polypyrrole matrix to form homogeneous composites i.e. anionic surfactant polyvinylsulphonic acid (PVSA) as well as non-ionic surfactants (polyethylene glycol p-(1,1,3,3tetramethylbutyl)-phenyl ether (Triton-X 100) and polyoxyethylene (20) sorbitan monolaurate (Tween 20). CV and EIS experiments were carried in the presence of the redox probe K 3 [Fe(CN) 6 ]. Diffusion coefficient was interpreted as a measure of electron movement within the composite polymer structure and rate constant was interpreted as a measure of the rate of oxidation and reduction of the redox probe. The highest value for diffusion coefficient and rate constant was obtained for Ppy/PVSA as 8.16 × 10 −12 cm 2 s −1 and 1.05 × 10 −5 cm s −1 respectively. The values obtained by CV and EIS were in good agreement.
Int. J. Electrochem …, 2011
Biocompatible and water soluble 3-mercaptopropionic acid capped gallium selenide nanocrystals wer... more Biocompatible and water soluble 3-mercaptopropionic acid capped gallium selenide nanocrystals were synthesized from hydrated gallium (III) perchlorate and selenide ions. The nanocrystals were nonfluorescent but showed a sharp UV-vis absorption maximum at 260 nm. Transmission electron micrographs showed the formation of high quality non-aggregated particles with an average diameter of 65 nm. Gold electrode modified with the capped nanocrystals was used as a platform for impedimetric genosensing using NH 2-5′-CCCACCGGTCCTTCATGTTC-3′ (probe) and 5′-GAACATGAAGGA CCGGTGGG-3′ (target) oligonucleotide sequences. The target oliginucleotide sequence is a component of 5-enolpyruvylshikimate-3-phosphate synthase, a common vector gene in glyphosate resistant transgenic plants. The impedimetric genosensor exhibited high sensitivity towards the target DNA (sensitivity = 11.61 Ω/nM) with a detection limit of 0.66 nM (3s, n = 8). The genosensor was able to discriminate between complementary, non-complementary and 3-base mismatched target sequences and maintained 87 % of its response towards the target DNA after one month.
Electrochimica Acta, 2014
Impedimetry and microscopy of electrosynthetic poly(propylene imine)-copolypyrrole conducting den... more Impedimetry and microscopy of electrosynthetic poly(propylene imine)-copolypyrrole conducting dendrimeric star copolymers, Electrochimica Acta (2014),
Sensors, 2010
A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy... more A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO 3 and HAuCl 4 using C 6 H 5 O 7 Na 3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20-50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10 −6 to 3.56 × 10 −4 M with a detection limit of 1.69 × 10 −7 M. The proposed method was simple, less time consuming and showed a high sensitivity.
Electrochimica Acta, 2014
Nanostructured poly(4-styrene sulphonic acid) and tantalum (IV) oxide-doped polyaniline nanocompo... more Nanostructured poly(4-styrene sulphonic acid) and tantalum (IV) oxide-doped polyaniline nanocompos-ite were synthesised and their electro-conductive properties were determined. The oxide was synthesizedusing a modified sol-gel method and then dispersed in acidic media through sonication and entrappedin-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped withpoly(4-styrene sulphonic acid). The oxides and novel polymeric nanocomposite were characterised withTEM, SEM, EDX, XRD, FTIR, UVvisible to ascertain elemental and phase composition, successful polymer-ization, doping, morphology and entrapment of the metal oxide nanoparticles. The electro-conductivityof the nanomaterial was interrogated using scanning electrochemical microscopy (SECM) and cyclicvoltammetry (CV). The material was then anchored on activated graphitic carbon and used in the designof an asymmetric supercapacitor cell using 6 M KOH aqueous electrolyte. Characteristically high specific capacitance values of 318.4 F/g with a corresponding energy and power densities of 1.57 kWh/kgand 0.435 kW/kg, respectively, were demonstrated. The cell also showed high coulombic efficiency of94.9% with a long cycle life and good cycle stability making the nanomaterial suitable for constructingsupercapacitor cell electrodes.
Electrochimica Acta, 2014
ABSTRACT