Dr. Syed M. Usman Ali | NED University of Engineering and Technology (original) (raw)

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Papers by Dr. Syed M. Usman Ali

Multilevel inverter (MLI) technology is gaining considerable attention of present research and is... more Multilevel inverter (MLI) technology is gaining considerable attention of present research and is a potential rival of conventional Sine wave inverter technology. It however faces limitations of its applications in medium voltage (MV) and High voltage (HV) such as Electrical Power Transmission & Distribution, Medium Voltage (MV) AC motor drives and a few Low Voltage (LV) applications. This is because of large hardware and complex control required for MLI. At low voltage, 2-level PWM Inverters still prevail. Present researches in MLI are towards minimizing hardware and improving upon its performance parameters, and owing to its high Power quality, it could be seen to be replacing 2-level PWM inverters in future. This paper takes thorough review of the Multilevel Inverter topologies, control strategies and its commercial applications as well as recent advancements carried out in this area

Sn doped ZnO nanorods were grown on p-type silicon substrate using sol-gel method. Impedance spec... more Sn doped ZnO nanorods were grown on p-type silicon substrate using sol-gel method. Impedance spectroscopy of Sn doped ZnO nanorods were recorded under dark and UV conditions to study the frequency dependent electrical parameters such as impedance and conductivity for the Sn doped ZnO nanorods MSM structure in the range of 1 Hz to 10 MHz. The Nyquist plot of Sn doped ZnO nanorods showed two semicircle arcs that correspond to the distribution of the grain boundaries and electrode process. It was observed that with the exposure of UV light the 2 nd semicircle arc that represents the electrode process is reduced. The conductivity plot revealed that the UV enhances the conduction of the Sn doped ZnO nanorods. SEM image showed the densily packed nanorods on the surface of silicon substrate, whereas XRD revealed that the grown nanorods have c-axis orientation.

Scripta Materialia, Jan 1, 2011

Note to users: The section "Articles in Press" contains peer reviewed accepted articles... more Note to users: The section "Articles in Press" contains peer reviewed accepted articles to be published in this journal. When the final article is assigned to an issue of the journal, the "Article in Press" version will be removed from this section and will appear in the associated ...

Biosensors & Bioelectronics, Jan 1, 2010

ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 μm in tip d... more ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 μm in tip diameter) and used as selective potentiometric sensor of intracellular free Mg2+. To functionalize the ZnO nanorods for selectivity of Mg2+, a polymeric membrane with Mg2+-selective ionophores were coated on the surface of the ZnO nanorods. These functionalized ZnO nanorods exhibited a Mg2+-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode within the concentration range from 500 nM to 100 mM. Two types of cells, human adipocytes and frog oocytes, were used for the intracellular Mg2+ measurements. The intracellular concentration of free Mg2+ in human adipocytes and frog oocytes were 0.4–0.5 and 0.8–0.9 mM, respectively. Such type of nanoelectrode device paves the way to enable analytical measurements in single living cells and to sense other bio-chemical species at the intracellular level.

Sensors and Actuators B-chemical, Jan 1, 2011

In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase o... more In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase onto zinc oxide (ZnO) nanowires. Zinc oxide nanowires with 80–150 nm in diameter and 900 nm to 1.5 μm in lengths were grown on the surface of a gold coated flexible plastic substrate. Uricase was electrostatically immobilized on the surface of well aligned ZnO nanowires resulting in a sensitive, selective, stable and reproducible uric acid biosensor. The potentiometric response of the ZnO sensor vs Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (1–650 μM) suitable for human blood serum. By applying a Nafion® membrane on the sensor the linear range could be extended to 1–1000 μM at the expense of an increased response time from 6.25 s to less than 9 s. On the other hand the membrane increased the sensor durability considerably. The sensor response was unaffected by normal concentrations of common interferents such as ascorbic acid, glucose, and urea.

Journal of Materials Chemistry, Jan 1, 2009

In this paper we present our new findings on the growth, characterization and nano-devices based ... more In this paper we present our new findings on the growth, characterization and nano-devices based on ZnO nanowires. We will limit the scope of this article to low temperature grown ZnO nanowires, due to the fact that low temperature growth is suitable for many applications. ...

Biosensors & Bioelectronics, Jan 1, 2010

In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor fo... more In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose. To adjust the sensor for intracellular glucose measurements, we grew hexagonal ZnO nanorods on the tip of a silver-covered borosilicate glass capillary (0.7 μm diameter) and coated them with the enzyme glucose oxidase. The enzyme-coated ZnO nanorods exhibited a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference was linear over the concentration range of interest (0.5–1000 μM). The measured glucose concentration in human adipocytes or frog oocytes using our ZnO-nanorod sensor was consistent with values of glucose concentration reported in the literature; furthermore, the sensor was able to show that insulin increased the intracellular glucose concentration. This nanoelectrode device demonstrates a simple technique to measure intracellular glucose concentration.

Sensors and Actuators B-chemical, Jan 1, 2010

In this study, a potentiometric intracellular glucose biosensor was fabricated by immobilization ... more In this study, a potentiometric intracellular glucose biosensor was fabricated by immobilization of glucose oxidase on nanoflake ZnO. Nanoflake ZnO with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose biosensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a logarithmic linear glucose-dependent electrochemical potential difference over a wide range of glucose concentration (500 nM–10 mM). Our measurements of intracellular glucose were consistent with the values of intracellular glucose concentrations reported in the literature. The monitoring capability of the sensor was demonstrated by following the increase in the intracellular glucose concentration induced by insulin in adipocytes and frog oocytes. In addition, the nanoflake ZnO material provided 1.8 times higher sensitivity than previously used ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the resulting nanosensor showed good performance in sensitivity, stability, selectivity, reproducibility, and anti-interference. All these results demonstrate that the nanoflake ZnO can provide a promising material for reliable measurements of intracellular glucose concentrations within single living cells.

Sensors and Actuators B-chemical, Jan 1, 2010

In this study, a potentiometric glucose biosensor was fabricated by immobilization of glucose oxi... more In this study, a potentiometric glucose biosensor was fabricated by immobilization of glucose oxidase on to zinc oxide nanowires. Zinc oxide nanowires with 250–300 nm diameters and approximately 1.2 μm lengths were grown on the surface of silver wires with a diameter of 250 μm. Glucose oxidase (GOD) was electrostatically immobilized on the surface of the well aligned zinc oxide nanowires resulting in sensitive, selective, stable and reproducible glucose biosensors. The potentiometric response vs. Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (0.5–1000 μM) suitable for intracellular glucose detection. By applying a membrane on the sensor the linear range could be extended to 0.5 μM to 10 mM, which increased the response time from less than 1 to 4 s. On the other hand the membrane increased the sensor durability considerably. The sensor response was unaffected by normal concentrations of common interferents with glucose sensing such as uric acid and ascorbic acid.

Sensors, Jan 1, 2009

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The dev... more ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.

Multilevel inverter (MLI) technology is gaining considerable attention of present research and is... more Multilevel inverter (MLI) technology is gaining considerable attention of present research and is a potential rival of conventional Sine wave inverter technology. It however faces limitations of its applications in medium voltage (MV) and High voltage (HV) such as Electrical Power Transmission & Distribution, Medium Voltage (MV) AC motor drives and a few Low Voltage (LV) applications. This is because of large hardware and complex control required for MLI. At low voltage, 2-level PWM Inverters still prevail. Present researches in MLI are towards minimizing hardware and improving upon its performance parameters, and owing to its high Power quality, it could be seen to be replacing 2-level PWM inverters in future. This paper takes thorough review of the Multilevel Inverter topologies, control strategies and its commercial applications as well as recent advancements carried out in this area

Sn doped ZnO nanorods were grown on p-type silicon substrate using sol-gel method. Impedance spec... more Sn doped ZnO nanorods were grown on p-type silicon substrate using sol-gel method. Impedance spectroscopy of Sn doped ZnO nanorods were recorded under dark and UV conditions to study the frequency dependent electrical parameters such as impedance and conductivity for the Sn doped ZnO nanorods MSM structure in the range of 1 Hz to 10 MHz. The Nyquist plot of Sn doped ZnO nanorods showed two semicircle arcs that correspond to the distribution of the grain boundaries and electrode process. It was observed that with the exposure of UV light the 2 nd semicircle arc that represents the electrode process is reduced. The conductivity plot revealed that the UV enhances the conduction of the Sn doped ZnO nanorods. SEM image showed the densily packed nanorods on the surface of silicon substrate, whereas XRD revealed that the grown nanorods have c-axis orientation.

Scripta Materialia, Jan 1, 2011

Note to users: The section "Articles in Press" contains peer reviewed accepted articles... more Note to users: The section "Articles in Press" contains peer reviewed accepted articles to be published in this journal. When the final article is assigned to an issue of the journal, the "Article in Press" version will be removed from this section and will appear in the associated ...

Biosensors & Bioelectronics, Jan 1, 2010

ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 μm in tip d... more ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 μm in tip diameter) and used as selective potentiometric sensor of intracellular free Mg2+. To functionalize the ZnO nanorods for selectivity of Mg2+, a polymeric membrane with Mg2+-selective ionophores were coated on the surface of the ZnO nanorods. These functionalized ZnO nanorods exhibited a Mg2+-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode within the concentration range from 500 nM to 100 mM. Two types of cells, human adipocytes and frog oocytes, were used for the intracellular Mg2+ measurements. The intracellular concentration of free Mg2+ in human adipocytes and frog oocytes were 0.4–0.5 and 0.8–0.9 mM, respectively. Such type of nanoelectrode device paves the way to enable analytical measurements in single living cells and to sense other bio-chemical species at the intracellular level.

Sensors and Actuators B-chemical, Jan 1, 2011

In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase o... more In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase onto zinc oxide (ZnO) nanowires. Zinc oxide nanowires with 80–150 nm in diameter and 900 nm to 1.5 μm in lengths were grown on the surface of a gold coated flexible plastic substrate. Uricase was electrostatically immobilized on the surface of well aligned ZnO nanowires resulting in a sensitive, selective, stable and reproducible uric acid biosensor. The potentiometric response of the ZnO sensor vs Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (1–650 μM) suitable for human blood serum. By applying a Nafion® membrane on the sensor the linear range could be extended to 1–1000 μM at the expense of an increased response time from 6.25 s to less than 9 s. On the other hand the membrane increased the sensor durability considerably. The sensor response was unaffected by normal concentrations of common interferents such as ascorbic acid, glucose, and urea.

Journal of Materials Chemistry, Jan 1, 2009

In this paper we present our new findings on the growth, characterization and nano-devices based ... more In this paper we present our new findings on the growth, characterization and nano-devices based on ZnO nanowires. We will limit the scope of this article to low temperature grown ZnO nanowires, due to the fact that low temperature growth is suitable for many applications. ...

Biosensors & Bioelectronics, Jan 1, 2010

In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor fo... more In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose. To adjust the sensor for intracellular glucose measurements, we grew hexagonal ZnO nanorods on the tip of a silver-covered borosilicate glass capillary (0.7 μm diameter) and coated them with the enzyme glucose oxidase. The enzyme-coated ZnO nanorods exhibited a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference was linear over the concentration range of interest (0.5–1000 μM). The measured glucose concentration in human adipocytes or frog oocytes using our ZnO-nanorod sensor was consistent with values of glucose concentration reported in the literature; furthermore, the sensor was able to show that insulin increased the intracellular glucose concentration. This nanoelectrode device demonstrates a simple technique to measure intracellular glucose concentration.

Sensors and Actuators B-chemical, Jan 1, 2010

In this study, a potentiometric intracellular glucose biosensor was fabricated by immobilization ... more In this study, a potentiometric intracellular glucose biosensor was fabricated by immobilization of glucose oxidase on nanoflake ZnO. Nanoflake ZnO with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose biosensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a logarithmic linear glucose-dependent electrochemical potential difference over a wide range of glucose concentration (500 nM–10 mM). Our measurements of intracellular glucose were consistent with the values of intracellular glucose concentrations reported in the literature. The monitoring capability of the sensor was demonstrated by following the increase in the intracellular glucose concentration induced by insulin in adipocytes and frog oocytes. In addition, the nanoflake ZnO material provided 1.8 times higher sensitivity than previously used ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the resulting nanosensor showed good performance in sensitivity, stability, selectivity, reproducibility, and anti-interference. All these results demonstrate that the nanoflake ZnO can provide a promising material for reliable measurements of intracellular glucose concentrations within single living cells.

Sensors and Actuators B-chemical, Jan 1, 2010

In this study, a potentiometric glucose biosensor was fabricated by immobilization of glucose oxi... more In this study, a potentiometric glucose biosensor was fabricated by immobilization of glucose oxidase on to zinc oxide nanowires. Zinc oxide nanowires with 250–300 nm diameters and approximately 1.2 μm lengths were grown on the surface of silver wires with a diameter of 250 μm. Glucose oxidase (GOD) was electrostatically immobilized on the surface of the well aligned zinc oxide nanowires resulting in sensitive, selective, stable and reproducible glucose biosensors. The potentiometric response vs. Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (0.5–1000 μM) suitable for intracellular glucose detection. By applying a membrane on the sensor the linear range could be extended to 0.5 μM to 10 mM, which increased the response time from less than 1 to 4 s. On the other hand the membrane increased the sensor durability considerably. The sensor response was unaffected by normal concentrations of common interferents with glucose sensing such as uric acid and ascorbic acid.

Sensors, Jan 1, 2009

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The dev... more ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.