Gymama Slaughter | University of Maryland Baltimore County (original) (raw)
Papers by Gymama Slaughter
Bioelectrocatalysis was demonstrated with palladium (Pd) nanowire array electrode via nonenzymati... more Bioelectrocatalysis was demonstrated with palladium (Pd) nanowire array electrode via nonenzymatic and en-zymatic methods for glucose, which was validated by the generation of anodic current in the presence of glucose. The vertically standing Pd nanowires used for the fabrication of the electrodes were on average 5.6 μm in length and 64 nm in diameter. In comparison, the nonenzymatic bioanode exhibited lower current densities and required the application of larger overpotential which resulted in a large cell voltage drop (V oc = 13.5 mV) and limited power production when assembled as a biofuel cell under physiological conditions (pH 7, 0.1 M phosphate buffer saline) with laccase covalently bounded to Pd nanowires as the biocathode. The glucose/O 2 biofuel cell was studied in phosphate buffer saline using the enzymatic bioanode that was developed with the co-immobilization of catalase and glucose oxidase on Pd nanowires and the laccase-Pd as the biocathode. The biofuel cell exhibited an open-circuit voltage of 0.506 V, delivered a maximum power density of 72 μW cm −2 at a cell voltage of 0.25 V and a short-circuit current density of 411 μA cm −2 when operating in 10 mM glucose. Such low-cost lightweight glucose/O 2 biofuel cells have a great promise to be optimized, miniaturized to power bio-implantable devices.
Enzymatic glucose biosensors are being developed to incorporate nanoscale materials with the biol... more Enzymatic glucose biosensors are being developed to incorporate nanoscale materials with the biological recognition elements to assist in the rapid and sensitive detection of glucose. Here we present a highly sensitive and selective glucose sensor based on capacitor circuit that is capable of selectively sensing glucose while simultaneously powering a small microelectronic device. Multi-walled carbon nanotubes (MWCNTs) is chemically modified with pyrroloquinoline quinone glucose dehydrogenase (PQQ-GDH) and bilirubin oxidase (BOD) at anode and cathode, respectively, in the biofuel cell arrangement. The input voltage (as low as 0.25 V) from the biofuel cell is converted to a stepped-up power and charged to the capacitor to the voltage of 1.8 V. The frequency of the charge/discharge cycle of the capacitor corresponded to the oxidation of glucose. The biofuel cell structure-based glucose sensor synergizes the advantages of both the glucose biosensor and biofuel cell. In addition, this glucose sensor favored a very high selectivity towards glucose in the presence of competing and non-competing analytes. It exhibited unprecedented sensitivity of 37.66 Hz/mM.cm 2 and a linear range of 1 to 20 mM. This innovative self-powered glucose sensor opens new doors for implementation of biofuel cells and capacitor circuits for medical diagnosis and powering therapeutic devices. Nanotechnology-based devices hold significant potential for improving the management of blood glucose levels in individuals suffering from diabetes by enabling highly sensitive and real-time monitoring of blood glucose. Such nano-biosensors can be used to emulate the body's physiological needs to trigger the delivery of insulin to provide effective therapeutics for type 1 diabetes. An estimated 1.25 million American children and adult have type 1 diabetes and projections are that the U.S. will have approximately 587,000 children living with type 1 diabetes by 2050 1. In type 1 diabetes, the insulin-secreting pancreatic islets cease to produce the 51-amino-acid peptide that is need for the regulation of blood glucose, thereby resulting in a deficiency in insulin and putting the patient at risk of hyperglycemia. The long term complications from hyperglycemia result in 2/3 of the costs of treating people with diabetes and lead to increased morbidity and mortality. Studies have shown that patients on intensive control programs who maintained their blood glucose levels close to normal experienced far less complications than patients who routinely maintained higher blood glucose levels 2, 3. These conditions require periodic sub-cutaneous insulin injections to regulate the patient's metabolism. At times, this can be painful, time-consuming and cumbersome, therefore, leading to poor patient compliance 4. Studies have also suggested that some diabetics choose not to strive for close blood glucose control due to the intrusiveness of current blood sampling, assay methods and to maintain lower or more normal blood glucose levels puts them at an increased risk of hypoglycemia 5. This situation is further exacerbated because blood sampling is relatively infrequent, compared to the rate of blood glucose fluctuations. To overcome the drawbacks of discrete glucose sampling, we report a self-powered glucose sensor based capacitor circuit that provides the desired continuous blood glucose sensing. The system is based on the generation and accumulation of electrical power in a capacitor via a charge pump integrated circuit as a result of the oxidation of glucose. We reasoned that the frequency of charging/discharging the capacitor would be an ideal glucose sensing scheme, with improved detection sensitivity and selectivity without the use of a potentiostat circuit or an external power source as used in glucometers and continuous glucose monitors (CGMs). The self-powered glucose sensor setup allows system miniaturization to be easily accomplished as well as the construction of sensing arrays. We therefore designed and developed an innovative self-powered glucose sensor based capacitor
A self-powered glucose biosensor (SPGS) system is fabricated and in vitro characterization of the... more A self-powered glucose biosensor (SPGS) system is fabricated and in vitro characterization of the power generation and charging frequency characteristics in glucose analyte are described. The bioelectrodes consist of compressed network of three-dimensional multi-walled carbon nanotubes with redox enzymes , pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) and laccase functioning as the anodic and cathodic catalyst, respectively. When operated in 45 mM glucose, the biofuel cell exhibited an open circuit voltage and power density of 681.8 mV and 67.86 mW/cm 2 at 335 mV, respectively, with a current density of 202.2 mA/cm 2. Moreover, at physiological glucose concentration (5 mM), the biofuel cell exhibits open circuit voltage and power density of 302.1 mV and 15.98 mW/cm 2 at 166.3 mV, respectively, with a current density of 100 mA/cm 2. The biofuel cell assembly produced a linear dynamic range of 0.5– 45 mM glucose. These findings show that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor by using a capacitor as the transducer element. By monitoring the capacitor charging frequencies, which are influenced by the concentration of the glucose analyte, a linear dynamic range of 0.5–35 mM glucose is observed. The operational stability of SPGS is monitored over a period of 63 days and is found to be stable with 15.38% and 11.76% drop in power density under continuous discharge in 10 mM and 20 mM glucose, respectively. These results demonstrate that SPGSs can simultaneously generate bioelectricity to power ultra-low powered devices and sense glucose.
Herein a system capable of simultaneously sensing glucose and harnessing sufficient energy to pow... more Herein a system capable of simultaneously sensing glucose and harnessing sufficient energy to power a digital device is presented. This system is powered by an enzymatic glucose biofuel cell consisting of pyroloquinoline quinone glucose dehydrogenase-modified bioanode and bilirubin oxidase-modified biocathode. The electrical parameters from a single biofuel cell were amplified to 1.4 V using a charge pump circuit consisting of a capacitive element that senses glucose. Furthermore, a steady output DC supply of 3.2 V was obtained by interfacing a step-up DC convertor circuit to the charge pump circuit. Such a system simultaneously senses glucose and harnesses energy in the presence of various glucose concentrations. The self-powered glucose biosensor exhibited an improved sensitivity of 86.42 Hz/cm 2 mM with a linear range extending to 20 mM when operating a digital device simultaneously. This is a 3.7-fold increase in sensor sensitivity when compared with previous self-powered glucose biosensors. This novel self-powered glucose biosensing system shows a promising future for powering implantable devices and assessing patient health.
Glucose biosensors have received significant attention in recent years due to the escalating mort... more Glucose biosensors have received significant attention in recent years due to the escalating mortality rate of diabetes mellitus. Although there is currently no cure for diabetes mellitus, individuals living with diabetes can lead a normal life by maintaining tight control of their blood glucose levels using glucose biosensors (e.g., glucometers). Current research in the field is focused on the optimization and improvement in the performance of glucose biosensors by employing a variety of glucose selective enzymes, mediators and semipermeable membranes to improve the electron transfer between the active center of the enzyme and the electrode substrate. Herein, we summarize the different semipermeable membranes used in the fabrication of the glucose biosensor, that result in improved biosensor sensitivity, selectivity, dynamic range, response time and stability.
Here, we describe the characterization of a self-powered glucose biosensor that is capable of gen... more Here, we describe the characterization of a self-powered glucose biosensor that is capable of generating electrical power from the biochemical energy stored in glucose to serve as the primary source of power for microelectronic devices. One self-powered glucose biosensor is based on multi-walled carbon nanotubes modified with pyroquinoline quinone glucose dehydro-genase (PQQ-GDH) and laccase at the bioanode and biocathode, respectively, whereas the other employed bilirubin oxidase at the biocathode. The self-power glucose biosensor employing the bilirubin oxidase biocathode operated at physiological condition and produced an enhanced peak power and current densities as compared with the self-powered glucose biosensor comprising of PQQ-GDH bioanode and laccase biocathode. The self-powered glucose biosensor employing bilirubin oxidase produced an average open circuit voltage of 0.480 V and delivered an average short circuit current density of 0.64 mA/cm 2 with a peak power density of 0.089 mW/cm 2. In addition, this self-powered glucose biosensor exhibited a linear dynamic range of 0.5–35 mM with a sensitivity of 12.221 Hz/mM·cm 2. The use of bilirubin oxidase as the biocathodic enzyme makes it a viable candidate as a potential power source for in vivo applications. Index Terms— Glucose biosensors, pyroquinoline quinone glucose dehydrogenase, bilirubin oxidase, laccase.
Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi... more Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane separators, while some have gained significant attention in the immobilization of enzymes or microorganisms within or behind the membrane at the electrode surface. The membrane material affects the transfer rate of the chemical species (e.g., fuel, oxygen molecules, and products) involved in the chemical reaction, which in turn has an impact on the performance of the biofuel cell. For enzymatic biofuel cells, Nafion, modified Nafion, and chitosan membranes have been used widely and continue to hold great promise in the long-term stability of enzymes and microorganisms encapsulated within them. This article provides a review of the most widely used membrane materials in the development of enzymatic and microbial biofuel cells.
A dual self-powered biosensing system integrated with energy amplification circuit is described, ... more A dual self-powered biosensing system integrated with energy amplification circuit is described, for simultaneously monitoring glucose and lactate. The self-powered biosensing system is based on the conventional enzymatic biofuel cell equipped with three 4 mm x 4 mm massively dense mesh network of multi-walled carbon nanotubes (MWCNTs) bioelectrodes in parallel configuration. The bioelectrodes employed pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) as the biocatalyst for the glucose oxidation and D-Lactate dehydrogenase (D-LDH) as the biocatalyst for lactate oxidation. A common laccase modified-MWCNTs bioelectrode served as the cathode for the reduction of molecular oxygen. Two charge pump circuits were coupled with 0.1 μF capacitors functioning as transducers. The advantages of employing capacitors were coupled with the efficient energy amplification of the charge pump circuit to amplify the power output from each of the biofuel and charge/discharge the corresponding capacitor. Under operating conditions, the open circuit voltages and short circuit current densities for 180 mg/dL glucose and 25 mM lactate were 339.2 mV and 228.75 µA/cm² and 370 mV and 66.17 µA/cm², respectively. The responses for glucose and lactate were linear up to 630 mg/dL and 30 mM with sensitivities of 20.11 Hz/ mM cm-2 and 9.869 Hz/ mM cm-2 , respectively. The potential of the described system was demonstrated to provide stable voltage and current output that was capable of driving the charge pump circuit integrated with the capacitor for simultaneously monitoring glucose and lactate. These results were in good agreement with those previously reported.
Glucose substrates are successfully harnessed to generate electricity in a membraneless biofuel c... more Glucose substrates are successfully harnessed to generate electricity in a membraneless biofuel cell with a mesh network of carbon nanotubes pyroquinoline quinone glucose dehydrogenase-modified anode and a laccase-modified cathode. Using glucose as a substrate, this glucose-oxygen biofuel cell is able to produce a steady current density of 337.5 µA/cm² and an open circuit voltage of 524 mV in 360 mg/dL glucose solution. Interestingly, the fuel cell in combination with a capacitor as the transducer element can also be utilized as a glucose monitor while generating electricity simultaneously to power small electronic devices, such as light emitting diode (LED). Moreover, the self-powered glucose monitor exhibited a linear dynamic range of 9 mg/dL to 630 mg/dL glucose. These results and device demonstrations suggest that further research into self-powered glucose monitors can provide major benefit in developing a novel autonomous implantable glucose monitor platform to greatly improve the quality of life for individuals living with diabetes.
— Implantable devices, such as implantable glucose biosensors, require a power source, which may ... more — Implantable devices, such as implantable glucose biosensors, require a power source, which may be provided by charging of a battery. The most immediate challenges facing implantable devices include (1) a high desire that implantable devices are self-powered and (2) the power source that can drive implantable devices must not add much weight to the implantable device. Therefore, it is important to explore innovative nanotechnologies that harvest energy from the environment for self-powering these implantable devices. Little or no work has been done on the conversion of the chemical energy stored in aluminum (Al)-phosphate cell based on the activation of Al using ZnO nanocrystal modifiers as a potential power source for implantable devices. In this work emphasis has been placed on the development Al-phosphate cell as a 'green' alternative to the traditional enzymatic biofuel cells for the conversion of the chemical energy stored in Al to power a light emitting diode (LED) via a capacitor energy storage circuit. The LED was powered by a capacitor based energy storage circuit using power generated by the Al-phosphate cell. Two Al-phosphate cells were connected in series and were used to charge the capacitors in parallel and then discharged the capacitors in series in order to amplify the voltage generated by the hybrid cells to power the LED. The optimal capacitance was observed to be 1000 µF for each hybrid cell. The use of capacitor charging system increase the power output from 210 µW to 4 mW compared to the two Al-phosphate hybrid cells connected in series without capacitors. This novel approach to energy generation has great potential to be utilized in powering implantable devices.
— In this work we characterize an Al/Au/ZnO anode for the development of an aluminum hybrid batte... more — In this work we characterize an Al/Au/ZnO anode for the development of an aluminum hybrid battery to power sensors using physiological buffers. ZnO nano-seed layers grown on the Al/Au electrode through a sol-gel deposition technique allow for increased electrical output over standard aluminum electrodes. The cell operated under varying neutral buffers allowing for smaller packaging, more environmental and safe operation for biomedical applications over popular alkaline batteries. Discharge of the aluminum anode is accompanied with the incorporation of phosphate in the electrolyte to allow for the safe formation of biocompatible crystals containing reduced phosphite structures bonded with alumina. The Al/Au/ZnO anode was paired with a cathode made of aggregated carbon nanotubes, buckypaper, to create a hybrid battery with enough power to power an average pacemaker and resulted in an open circuit voltage of 0.767 V. A maximum power density of 2.63 mW/ cm 2 was observed in physiological saline buffer at a cell voltage and current density of 147 mV and 1.77 mA/ cm 2 , respectively.
—We present the low-cost microfabrication of three-dimensional Au nanotip pyramidal electrode arr... more —We present the low-cost microfabrication of three-dimensional Au nanotip pyramidal electrode array by selective and anisotropic etching n-type Si in tetramethylammonium hydroxide (TMAH) solution. The influence of the TMAH etchant concentration and bath temperature on the on lithographically patterned Si etch rate was investigated. Using buffer oxidize etching technique of thermal oxide, sputtered metallic Au nanotip pyramidal electrode array are released from the resultant inverted pyramid Si master mold. The Au nanotip pyramidal electrode array with average size of 5.34 x 5.34 µm, pitch size as small as 198 nm, and individual tip diameter as small as 62 nm were successfully fabricated using a low-cost effective beaker chemistry method. Glucose oxidase (GOx) immobilized on the Au nanotip pyramidal electrode array retains its biocatalytic activity and offers a fast sensitive glucose quantification. The combination of Au nanotip pyramidal electrode array with GOx enhances the performance of the glucose biosensor. The fabricated glucose biosensor exhibits a linear dynamic response up to 18 mM glucose and a sensitivity of 122.5 μA cm-2 mM-1 .
— Herein a glucose biofuel cell capable of producing micro-watts power has been presented. The bi... more — Herein a glucose biofuel cell capable of producing micro-watts power has been presented. The bioanode and the biocathode were fabricated using glucose oxidase and oxygen reducing laccase, respectively immobilized on a 4 x 4 Au nanotip pyramidal electrode array having a tip diameter of ~62 nm with an electroactive surface area of 0.04 cm². The power generating capability of the glucose biofuel cell was characterized in the presence of 5 mM, 10 mM and 20 mM glucose solution (pH 7) at 37° C to mimic the physiologic conditions. An open circuit voltage of 562.1 mV with a maximum power density of 112.21 µW cm-2 at a cell voltage of 270.4 mV was delivered by the glucose biofuel cell operating in 20 mM glucose. The use for the 4 x 4 Au nanotip pyramidal electrode array provides a novel approach to improve the electroactive surface area for enzyme immobilization, in addition to enabling the electrochemical energy generation via direct electron transfer. The as-fabricated glucose biofuel cell has a great potential to be employed in powering low-power implantable bioelectronic devices.
Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mech... more Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mechanism for preventing excessive elevation in blood glucose. Impaired glucose metabolism and insulin resistance have been linked to excess body fat composition. Here, we quantify abdominal muscle and abdominal adipose tissue compartments in a large nonhuman primate, the baboon, and investigate their relationship with serum glucose response to a hyperglycemic challenge.
Methods: Five female baboons were fasted for 16 hours prior to 90 minute body imaging experiment that consisted of a 20-min baseline, followed by a bolus infusion of glucose (500mg/kg). The blood glucose was sampled at regular intervals. The total volumes of the muscle, visceral and subcutaneous adipose tissue were measured.
Results and discussion: We found that adipose tissue composition predicted fluctuations in glucose responses to a hyperglycemic challenge of a non-human primate. Animals with higher visceral adiposity showed significantly reduced glucose elimination. The glucose responses were positively correlated with body weight, visceral and muscle fat (p < 0.005). Polynomial regression analysis showed that body weight, visceral and muscle were significant predictors of serum glucose responses (p < 0.001).
Conclusions:These results reveal the similarity between humans and baboons with respect to glucose metabolism and strengthen the utility of baboon for biomedical research.
Key Words: Hyperglycemic Challenge; Perfusion Imaging; Body Fat Composition.
The 8th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems, 2013
ABSTRACT
Journal of Non-Crystalline Solids, 1989
An extended glass forming region has been identified in the Li 2 O:P 2 O 5 :Nb 2 O 5 system. Temp... more An extended glass forming region has been identified in the Li 2 O:P 2 O 5 :Nb 2 O 5 system. Temperature and composition dependence of conductivity have been measured. A high ionic conductivity value 2 × 10 −6 Ω −1 cm −1 at room temperature has been found for the ...
IEEE Sensors Journal, 2000
Bioelectrocatalysis was demonstrated with palladium (Pd) nanowire array electrode via nonenzymati... more Bioelectrocatalysis was demonstrated with palladium (Pd) nanowire array electrode via nonenzymatic and en-zymatic methods for glucose, which was validated by the generation of anodic current in the presence of glucose. The vertically standing Pd nanowires used for the fabrication of the electrodes were on average 5.6 μm in length and 64 nm in diameter. In comparison, the nonenzymatic bioanode exhibited lower current densities and required the application of larger overpotential which resulted in a large cell voltage drop (V oc = 13.5 mV) and limited power production when assembled as a biofuel cell under physiological conditions (pH 7, 0.1 M phosphate buffer saline) with laccase covalently bounded to Pd nanowires as the biocathode. The glucose/O 2 biofuel cell was studied in phosphate buffer saline using the enzymatic bioanode that was developed with the co-immobilization of catalase and glucose oxidase on Pd nanowires and the laccase-Pd as the biocathode. The biofuel cell exhibited an open-circuit voltage of 0.506 V, delivered a maximum power density of 72 μW cm −2 at a cell voltage of 0.25 V and a short-circuit current density of 411 μA cm −2 when operating in 10 mM glucose. Such low-cost lightweight glucose/O 2 biofuel cells have a great promise to be optimized, miniaturized to power bio-implantable devices.
Enzymatic glucose biosensors are being developed to incorporate nanoscale materials with the biol... more Enzymatic glucose biosensors are being developed to incorporate nanoscale materials with the biological recognition elements to assist in the rapid and sensitive detection of glucose. Here we present a highly sensitive and selective glucose sensor based on capacitor circuit that is capable of selectively sensing glucose while simultaneously powering a small microelectronic device. Multi-walled carbon nanotubes (MWCNTs) is chemically modified with pyrroloquinoline quinone glucose dehydrogenase (PQQ-GDH) and bilirubin oxidase (BOD) at anode and cathode, respectively, in the biofuel cell arrangement. The input voltage (as low as 0.25 V) from the biofuel cell is converted to a stepped-up power and charged to the capacitor to the voltage of 1.8 V. The frequency of the charge/discharge cycle of the capacitor corresponded to the oxidation of glucose. The biofuel cell structure-based glucose sensor synergizes the advantages of both the glucose biosensor and biofuel cell. In addition, this glucose sensor favored a very high selectivity towards glucose in the presence of competing and non-competing analytes. It exhibited unprecedented sensitivity of 37.66 Hz/mM.cm 2 and a linear range of 1 to 20 mM. This innovative self-powered glucose sensor opens new doors for implementation of biofuel cells and capacitor circuits for medical diagnosis and powering therapeutic devices. Nanotechnology-based devices hold significant potential for improving the management of blood glucose levels in individuals suffering from diabetes by enabling highly sensitive and real-time monitoring of blood glucose. Such nano-biosensors can be used to emulate the body's physiological needs to trigger the delivery of insulin to provide effective therapeutics for type 1 diabetes. An estimated 1.25 million American children and adult have type 1 diabetes and projections are that the U.S. will have approximately 587,000 children living with type 1 diabetes by 2050 1. In type 1 diabetes, the insulin-secreting pancreatic islets cease to produce the 51-amino-acid peptide that is need for the regulation of blood glucose, thereby resulting in a deficiency in insulin and putting the patient at risk of hyperglycemia. The long term complications from hyperglycemia result in 2/3 of the costs of treating people with diabetes and lead to increased morbidity and mortality. Studies have shown that patients on intensive control programs who maintained their blood glucose levels close to normal experienced far less complications than patients who routinely maintained higher blood glucose levels 2, 3. These conditions require periodic sub-cutaneous insulin injections to regulate the patient's metabolism. At times, this can be painful, time-consuming and cumbersome, therefore, leading to poor patient compliance 4. Studies have also suggested that some diabetics choose not to strive for close blood glucose control due to the intrusiveness of current blood sampling, assay methods and to maintain lower or more normal blood glucose levels puts them at an increased risk of hypoglycemia 5. This situation is further exacerbated because blood sampling is relatively infrequent, compared to the rate of blood glucose fluctuations. To overcome the drawbacks of discrete glucose sampling, we report a self-powered glucose sensor based capacitor circuit that provides the desired continuous blood glucose sensing. The system is based on the generation and accumulation of electrical power in a capacitor via a charge pump integrated circuit as a result of the oxidation of glucose. We reasoned that the frequency of charging/discharging the capacitor would be an ideal glucose sensing scheme, with improved detection sensitivity and selectivity without the use of a potentiostat circuit or an external power source as used in glucometers and continuous glucose monitors (CGMs). The self-powered glucose sensor setup allows system miniaturization to be easily accomplished as well as the construction of sensing arrays. We therefore designed and developed an innovative self-powered glucose sensor based capacitor
A self-powered glucose biosensor (SPGS) system is fabricated and in vitro characterization of the... more A self-powered glucose biosensor (SPGS) system is fabricated and in vitro characterization of the power generation and charging frequency characteristics in glucose analyte are described. The bioelectrodes consist of compressed network of three-dimensional multi-walled carbon nanotubes with redox enzymes , pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) and laccase functioning as the anodic and cathodic catalyst, respectively. When operated in 45 mM glucose, the biofuel cell exhibited an open circuit voltage and power density of 681.8 mV and 67.86 mW/cm 2 at 335 mV, respectively, with a current density of 202.2 mA/cm 2. Moreover, at physiological glucose concentration (5 mM), the biofuel cell exhibits open circuit voltage and power density of 302.1 mV and 15.98 mW/cm 2 at 166.3 mV, respectively, with a current density of 100 mA/cm 2. The biofuel cell assembly produced a linear dynamic range of 0.5– 45 mM glucose. These findings show that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor by using a capacitor as the transducer element. By monitoring the capacitor charging frequencies, which are influenced by the concentration of the glucose analyte, a linear dynamic range of 0.5–35 mM glucose is observed. The operational stability of SPGS is monitored over a period of 63 days and is found to be stable with 15.38% and 11.76% drop in power density under continuous discharge in 10 mM and 20 mM glucose, respectively. These results demonstrate that SPGSs can simultaneously generate bioelectricity to power ultra-low powered devices and sense glucose.
Herein a system capable of simultaneously sensing glucose and harnessing sufficient energy to pow... more Herein a system capable of simultaneously sensing glucose and harnessing sufficient energy to power a digital device is presented. This system is powered by an enzymatic glucose biofuel cell consisting of pyroloquinoline quinone glucose dehydrogenase-modified bioanode and bilirubin oxidase-modified biocathode. The electrical parameters from a single biofuel cell were amplified to 1.4 V using a charge pump circuit consisting of a capacitive element that senses glucose. Furthermore, a steady output DC supply of 3.2 V was obtained by interfacing a step-up DC convertor circuit to the charge pump circuit. Such a system simultaneously senses glucose and harnesses energy in the presence of various glucose concentrations. The self-powered glucose biosensor exhibited an improved sensitivity of 86.42 Hz/cm 2 mM with a linear range extending to 20 mM when operating a digital device simultaneously. This is a 3.7-fold increase in sensor sensitivity when compared with previous self-powered glucose biosensors. This novel self-powered glucose biosensing system shows a promising future for powering implantable devices and assessing patient health.
Glucose biosensors have received significant attention in recent years due to the escalating mort... more Glucose biosensors have received significant attention in recent years due to the escalating mortality rate of diabetes mellitus. Although there is currently no cure for diabetes mellitus, individuals living with diabetes can lead a normal life by maintaining tight control of their blood glucose levels using glucose biosensors (e.g., glucometers). Current research in the field is focused on the optimization and improvement in the performance of glucose biosensors by employing a variety of glucose selective enzymes, mediators and semipermeable membranes to improve the electron transfer between the active center of the enzyme and the electrode substrate. Herein, we summarize the different semipermeable membranes used in the fabrication of the glucose biosensor, that result in improved biosensor sensitivity, selectivity, dynamic range, response time and stability.
Here, we describe the characterization of a self-powered glucose biosensor that is capable of gen... more Here, we describe the characterization of a self-powered glucose biosensor that is capable of generating electrical power from the biochemical energy stored in glucose to serve as the primary source of power for microelectronic devices. One self-powered glucose biosensor is based on multi-walled carbon nanotubes modified with pyroquinoline quinone glucose dehydro-genase (PQQ-GDH) and laccase at the bioanode and biocathode, respectively, whereas the other employed bilirubin oxidase at the biocathode. The self-power glucose biosensor employing the bilirubin oxidase biocathode operated at physiological condition and produced an enhanced peak power and current densities as compared with the self-powered glucose biosensor comprising of PQQ-GDH bioanode and laccase biocathode. The self-powered glucose biosensor employing bilirubin oxidase produced an average open circuit voltage of 0.480 V and delivered an average short circuit current density of 0.64 mA/cm 2 with a peak power density of 0.089 mW/cm 2. In addition, this self-powered glucose biosensor exhibited a linear dynamic range of 0.5–35 mM with a sensitivity of 12.221 Hz/mM·cm 2. The use of bilirubin oxidase as the biocathodic enzyme makes it a viable candidate as a potential power source for in vivo applications. Index Terms— Glucose biosensors, pyroquinoline quinone glucose dehydrogenase, bilirubin oxidase, laccase.
Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi... more Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane separators, while some have gained significant attention in the immobilization of enzymes or microorganisms within or behind the membrane at the electrode surface. The membrane material affects the transfer rate of the chemical species (e.g., fuel, oxygen molecules, and products) involved in the chemical reaction, which in turn has an impact on the performance of the biofuel cell. For enzymatic biofuel cells, Nafion, modified Nafion, and chitosan membranes have been used widely and continue to hold great promise in the long-term stability of enzymes and microorganisms encapsulated within them. This article provides a review of the most widely used membrane materials in the development of enzymatic and microbial biofuel cells.
A dual self-powered biosensing system integrated with energy amplification circuit is described, ... more A dual self-powered biosensing system integrated with energy amplification circuit is described, for simultaneously monitoring glucose and lactate. The self-powered biosensing system is based on the conventional enzymatic biofuel cell equipped with three 4 mm x 4 mm massively dense mesh network of multi-walled carbon nanotubes (MWCNTs) bioelectrodes in parallel configuration. The bioelectrodes employed pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) as the biocatalyst for the glucose oxidation and D-Lactate dehydrogenase (D-LDH) as the biocatalyst for lactate oxidation. A common laccase modified-MWCNTs bioelectrode served as the cathode for the reduction of molecular oxygen. Two charge pump circuits were coupled with 0.1 μF capacitors functioning as transducers. The advantages of employing capacitors were coupled with the efficient energy amplification of the charge pump circuit to amplify the power output from each of the biofuel and charge/discharge the corresponding capacitor. Under operating conditions, the open circuit voltages and short circuit current densities for 180 mg/dL glucose and 25 mM lactate were 339.2 mV and 228.75 µA/cm² and 370 mV and 66.17 µA/cm², respectively. The responses for glucose and lactate were linear up to 630 mg/dL and 30 mM with sensitivities of 20.11 Hz/ mM cm-2 and 9.869 Hz/ mM cm-2 , respectively. The potential of the described system was demonstrated to provide stable voltage and current output that was capable of driving the charge pump circuit integrated with the capacitor for simultaneously monitoring glucose and lactate. These results were in good agreement with those previously reported.
Glucose substrates are successfully harnessed to generate electricity in a membraneless biofuel c... more Glucose substrates are successfully harnessed to generate electricity in a membraneless biofuel cell with a mesh network of carbon nanotubes pyroquinoline quinone glucose dehydrogenase-modified anode and a laccase-modified cathode. Using glucose as a substrate, this glucose-oxygen biofuel cell is able to produce a steady current density of 337.5 µA/cm² and an open circuit voltage of 524 mV in 360 mg/dL glucose solution. Interestingly, the fuel cell in combination with a capacitor as the transducer element can also be utilized as a glucose monitor while generating electricity simultaneously to power small electronic devices, such as light emitting diode (LED). Moreover, the self-powered glucose monitor exhibited a linear dynamic range of 9 mg/dL to 630 mg/dL glucose. These results and device demonstrations suggest that further research into self-powered glucose monitors can provide major benefit in developing a novel autonomous implantable glucose monitor platform to greatly improve the quality of life for individuals living with diabetes.
— Implantable devices, such as implantable glucose biosensors, require a power source, which may ... more — Implantable devices, such as implantable glucose biosensors, require a power source, which may be provided by charging of a battery. The most immediate challenges facing implantable devices include (1) a high desire that implantable devices are self-powered and (2) the power source that can drive implantable devices must not add much weight to the implantable device. Therefore, it is important to explore innovative nanotechnologies that harvest energy from the environment for self-powering these implantable devices. Little or no work has been done on the conversion of the chemical energy stored in aluminum (Al)-phosphate cell based on the activation of Al using ZnO nanocrystal modifiers as a potential power source for implantable devices. In this work emphasis has been placed on the development Al-phosphate cell as a 'green' alternative to the traditional enzymatic biofuel cells for the conversion of the chemical energy stored in Al to power a light emitting diode (LED) via a capacitor energy storage circuit. The LED was powered by a capacitor based energy storage circuit using power generated by the Al-phosphate cell. Two Al-phosphate cells were connected in series and were used to charge the capacitors in parallel and then discharged the capacitors in series in order to amplify the voltage generated by the hybrid cells to power the LED. The optimal capacitance was observed to be 1000 µF for each hybrid cell. The use of capacitor charging system increase the power output from 210 µW to 4 mW compared to the two Al-phosphate hybrid cells connected in series without capacitors. This novel approach to energy generation has great potential to be utilized in powering implantable devices.
— In this work we characterize an Al/Au/ZnO anode for the development of an aluminum hybrid batte... more — In this work we characterize an Al/Au/ZnO anode for the development of an aluminum hybrid battery to power sensors using physiological buffers. ZnO nano-seed layers grown on the Al/Au electrode through a sol-gel deposition technique allow for increased electrical output over standard aluminum electrodes. The cell operated under varying neutral buffers allowing for smaller packaging, more environmental and safe operation for biomedical applications over popular alkaline batteries. Discharge of the aluminum anode is accompanied with the incorporation of phosphate in the electrolyte to allow for the safe formation of biocompatible crystals containing reduced phosphite structures bonded with alumina. The Al/Au/ZnO anode was paired with a cathode made of aggregated carbon nanotubes, buckypaper, to create a hybrid battery with enough power to power an average pacemaker and resulted in an open circuit voltage of 0.767 V. A maximum power density of 2.63 mW/ cm 2 was observed in physiological saline buffer at a cell voltage and current density of 147 mV and 1.77 mA/ cm 2 , respectively.
—We present the low-cost microfabrication of three-dimensional Au nanotip pyramidal electrode arr... more —We present the low-cost microfabrication of three-dimensional Au nanotip pyramidal electrode array by selective and anisotropic etching n-type Si in tetramethylammonium hydroxide (TMAH) solution. The influence of the TMAH etchant concentration and bath temperature on the on lithographically patterned Si etch rate was investigated. Using buffer oxidize etching technique of thermal oxide, sputtered metallic Au nanotip pyramidal electrode array are released from the resultant inverted pyramid Si master mold. The Au nanotip pyramidal electrode array with average size of 5.34 x 5.34 µm, pitch size as small as 198 nm, and individual tip diameter as small as 62 nm were successfully fabricated using a low-cost effective beaker chemistry method. Glucose oxidase (GOx) immobilized on the Au nanotip pyramidal electrode array retains its biocatalytic activity and offers a fast sensitive glucose quantification. The combination of Au nanotip pyramidal electrode array with GOx enhances the performance of the glucose biosensor. The fabricated glucose biosensor exhibits a linear dynamic response up to 18 mM glucose and a sensitivity of 122.5 μA cm-2 mM-1 .
— Herein a glucose biofuel cell capable of producing micro-watts power has been presented. The bi... more — Herein a glucose biofuel cell capable of producing micro-watts power has been presented. The bioanode and the biocathode were fabricated using glucose oxidase and oxygen reducing laccase, respectively immobilized on a 4 x 4 Au nanotip pyramidal electrode array having a tip diameter of ~62 nm with an electroactive surface area of 0.04 cm². The power generating capability of the glucose biofuel cell was characterized in the presence of 5 mM, 10 mM and 20 mM glucose solution (pH 7) at 37° C to mimic the physiologic conditions. An open circuit voltage of 562.1 mV with a maximum power density of 112.21 µW cm-2 at a cell voltage of 270.4 mV was delivered by the glucose biofuel cell operating in 20 mM glucose. The use for the 4 x 4 Au nanotip pyramidal electrode array provides a novel approach to improve the electroactive surface area for enzyme immobilization, in addition to enabling the electrochemical energy generation via direct electron transfer. The as-fabricated glucose biofuel cell has a great potential to be employed in powering low-power implantable bioelectronic devices.
Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mech... more Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mechanism for preventing excessive elevation in blood glucose. Impaired glucose metabolism and insulin resistance have been linked to excess body fat composition. Here, we quantify abdominal muscle and abdominal adipose tissue compartments in a large nonhuman primate, the baboon, and investigate their relationship with serum glucose response to a hyperglycemic challenge.
Methods: Five female baboons were fasted for 16 hours prior to 90 minute body imaging experiment that consisted of a 20-min baseline, followed by a bolus infusion of glucose (500mg/kg). The blood glucose was sampled at regular intervals. The total volumes of the muscle, visceral and subcutaneous adipose tissue were measured.
Results and discussion: We found that adipose tissue composition predicted fluctuations in glucose responses to a hyperglycemic challenge of a non-human primate. Animals with higher visceral adiposity showed significantly reduced glucose elimination. The glucose responses were positively correlated with body weight, visceral and muscle fat (p < 0.005). Polynomial regression analysis showed that body weight, visceral and muscle were significant predictors of serum glucose responses (p < 0.001).
Conclusions:These results reveal the similarity between humans and baboons with respect to glucose metabolism and strengthen the utility of baboon for biomedical research.
Key Words: Hyperglycemic Challenge; Perfusion Imaging; Body Fat Composition.
The 8th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems, 2013
ABSTRACT
Journal of Non-Crystalline Solids, 1989
An extended glass forming region has been identified in the Li 2 O:P 2 O 5 :Nb 2 O 5 system. Temp... more An extended glass forming region has been identified in the Li 2 O:P 2 O 5 :Nb 2 O 5 system. Temperature and composition dependence of conductivity have been measured. A high ionic conductivity value 2 × 10 −6 Ω −1 cm −1 at room temperature has been found for the ...
IEEE Sensors Journal, 2000
Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mech... more Background: Blood glucose levels regulate the rate of insulin secretion, which is the body’s mechanism for preventing excessive elevation in blood glucose. Impaired glucose metabolism and insulin resistance have been linked to excess body fat composition. Here, we quantify abdominal muscle and abdominal adipose tissue compartments in a large nonhuman primate, the baboon, and investigate their relationship with serum glucose response to a hyperglycemic challenge.
Methods: Five female baboons were fasted for 16 hours prior to 90 minute body imaging experiment that consisted of a 20-min baseline, followed by a bolus infusion of glucose (500mg/kg). The blood glucose was sampled at regular intervals. The total volumes of the muscle, visceral and subcutaneous adipose tissue were measured.
Results and discussion: We found that adipose tissue composition predicted fluctuations in glucose responses to a hyperglycemic challenge of a non-human primate. Animals with higher visceral adiposity showed significantly reduced glucose elimination. The glucose responses were positively correlated with body weight, visceral and muscle fat (p < 0.005). Polynomial regression analysis showed that body weight, visceral and muscle were significant predictors of serum glucose responses (p < 0.001).
Conclusions:These results reveal the similarity between humans and baboons with respect to glucose metabolism and strengthen the utility of baboon for biomedical research.
Key Words: Hyperglycemic Challenge; Perfusion Imaging; Body Fat Composition.