Gymama Slaughter

Design of a subcutaneous implantable biochip for monitoring of glucose and lactate

The design, fabrication, and in-vitro evaluation of an amperometric biochip that is designed for the continuous in vivo monitoring of physiological analytes is described. The 2 /spl times/4 /spl times/0.5 mm biochip contains two platinum working enzyme electrodes that adopt the microdisc array design to minimize diffusional limitations associated with enzyme kinetics. This configuration permits either dual analyte sensing or a differential response analytical methodology during amperometric detection of a single analyte. The working enzyme electrodes are complemented by a large area platinized platinum counter electrode and a silver reference electrode. The biorecognition layer of the working electrodes was fabricated from around 1.0-/spl mu/m-thick composite membrane of principally tetraethylene glycol (TEGDA) cross-linked poly(2-hydroxyethyl methacrylate) that also contained a derivatized polypyrrole component and a biomimetic methacrylate component with pendant phosphorylcholine groups. These two additional components were introduced to provide interference screening and in vivo biocompatibility, respectively. This composite membrane was used to immobilize glucose oxidase and lactate oxidase onto both planar and microdisc array electrode designs, which were then used to assay for in vitro glucose and lactate, respectively. The glucose biosensor exhibited a dynamic linear range of 0.10-13.0 mM glucose with a response time (t/sub 95/) of 50 s. The immobilized glucose oxidase within the hydrogel yielded a K/sub m(app)/ of 35 mM, not significantly different from that for the native, solution-borne enzyme (33 mM). The microdisc array biosensor displayed linearity for assayed lactate up to 90 mM, which represented a 30-fold increase in linear dynamic lactate range compared to the biosensor with the planar electrode configuration. Preliminary in vitro operational stability tests performed with the microdisc array lactate biosensor demonstrated retention of 80% initial biosensor response after five days of continuous operation in buffer under physiologic conditions of pH and temperature.

Enzymatic Glucose Biofuel Cell and its Application

Biofuel cells have received significant attention in the last few decades due to its potential application as alternative energy sources and advantages over conventional fuel cells. This review summarizes different types of glucose biofuel cells with emphasis on enzymatic glucose biofuel cells. Unlike conventional fuel cells, which use fuel such as ethanol, methanol, formic acid, etc. to generate electricity, enzymatic glucose biofuel cells convert chemical energy stored in glucose into electricity. Energy generating from complex sugar is now possible due to the most common glucose selective enzymes, Glucose Oxidase (GOx) and Pyroquinoline Quinone Glucose Dehydrogenase (PQQ-GDH). Glucose as a fuel source is cost-efficient because it is readily abundant and offers a clean source of power. The micro-power generated from the selective glucose/ O2 redox reactions can be used to power ultra-low powered bioelectronic devices. In addition, in vivo glucose biofuel cell implantations and potential applications are highlighted.

A self-powered glucose biosensing system.

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 µW/cm(2) at 335 mV, respectively, with a current density of 202.2 µA/cm(2). Moreover, at physiological glucose concentration (5mM), the biofuel cell exhibits open circuit voltage and power density of 302.1 mV and 15.98 µW/cm(2) at 166.3 mV, respectively, with a current density of 100 µA/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 10mM and 20mM glucose, respectively. These results demonstrate that SPGSs can simultaneously generate bioelectricity to power ultra-low powered devices and sense glucose.

An impedimetric biosensor based on PC 12 cells for the monitoring of exogenous agents

The effect of exogenous agents on the complex impedance of PC 12 cells that were cultured to confluency on 250-mum gold microdot electrodes fabricated within 8-well cell culture biochips was studied. Surface attachment of PC 12 cells to gold microelectrodes was accomplished using cysteamine SAMs covalently derivatized with laminin. The impedimetric response of PC 12 cells that undergo calcium exocytosis in the presence of calcimycin, nifedipine, mannitol and carbachol were identified. Treatment with carbachol induces muscarinic receptor-dependent rises in free cytosolic Ca(2+). Experiments with calcimycin and nifedipine were carried out to clarify the relationship between these two receptor-triggered events. In particular, it is believed to mediate intracellularly the release of Ca(2+) from non-mitochondrial stores. We also examined cellular impedance responsiveness of PC 12 cells in response to phenotypic alteration especially with regard to modulation of ion fluxes using nerve growth factor (NGF), dexamethasone and forskolin. Our results demonstrate that a change in electrophysiological behavior, such as exocytosis of cytosolic Ca(2+) is detectable using impedance spectroscopy, and therefore support the results of impedance fluctuation to be attributed to ion-fluxes.

Fabrication of Nanoindented Electrodes for Glucose Detection

Background: The objective of this article was to design, fabricate, and evaluate a novel type of glucose biosensors based on the use of atomic force microscopy to create nanoindented electrodes (NIDEs) for the selective detection of glucose. Methods: Atomic force microscopy nanoindentation techniques were extended to covalently immobilized glucose oxidase on NIDEs via composite hydrogel membranes composed of interpenetrating networks of inherently conductive poly(3,4-ethylenedioxythiophene) tetramethacrylate grown within ultraviolet cross-linked hydroxyethylmethacrylate-based hydrogels to produce an in vitro amperometric NIDE biosensor for the long-term monitoring of glucose. Results: The calibration curve for glucose was linear from 0.25 to 20 mM. Results showed that the NIDE glucose biosensor has a much higher detection sensitivity of 0.32 μA/mM and rapid response times (<5 seconds). There was no interference from the competing interferent (fructose) present; the only interference was from species that react with H2O2 (ascorbic acid). The linear equation was B response (μA) = 0.323 [glucose] (mM) + 0.634 (μA); n = 24, r 2 = 0.994. Conclusion: Results showed that the resultant NIDE glucose biosensor increases the dynamic range, device sensitivity, and response time and has excellent detecting performance for glucose.

Highly Selective and Sensitive Self-Powered Glucose Sensor Based on Capacitor Circuit

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.cm2 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.

Self-powered glucose biosensor operating under physiological conditions

Here we describe the characterization of a self-powered glucose biosensor comprising of a multi-walled carbon nanotubes (MWCNTs) modified with pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) bioanode and bilirubin oxidase biocathode at physiological conditions. The assembly shows an enhancement in peak power and current densities as compared to the self-powered glucose biosensor comprising of PQQ-GDH bioanode and laccase biocathode. The assembly produced a maximum open circuit voltage of 480.1 mV and short circuit current density of 640 μA/cm2 with a peak power density of 89.27 μW/cm2. The self-powered glucose biosensor exhibited an extended linear dynamic range of 0.1 mM to 35 mM with a sensitivity of 12.221 Hz/mM cm2. The use of bilirubin oxidase as the cathodic enzyme in addition to the design of biofuel cell assembly makes it a viable candidate as a potential power source for bioelectronics devices.

Artificial Neural Network for Temporal Impedance Recognition of Neurotoxins

The design, development and in-vitro evaluation of an impedimetric neurotoxicity cell-based biosensor that is designed for real time monitoring of changes in electrophysiological behavior under the influence of neurotoxins is described. The electrical cell impedance sensing (ECIS) system [ECIS 8W1E element array of gold electrodes] is used as a substrate for the culture of rat pheochromocytoma (PC 12) cells. The neurotoxicity biosensor is a microfabricated solid state device that mimics the natural environment of PC 12 cells that are responsive to neurotoxins. The PC 12 neurotoxicity biosensors are complemented by artificial neural networks (ANNs) to recognize the impedance profiles of the cells under the influence of a neurotoxin. The neurotoxins were rotenone (Rot), okadaic acid (OA) and peroxynitrite (Per), which are all known to induce cell death in PC 12 cells. Three multilayer feedforward artificial neural network models were developed using a back-propagation algorithm for pattern recognition of neurotoxins. The neurotoxin network (NTN) and the neurotoxin concentration network (NTCN), were trained with data from all the neurotoxins and the cascade network (NTN_NTCN) was developed by combining both the NTN and NTCN. The cascade network was developed to screen against false positives. The neurotoxicity biosensor coupled with these networks allowed for the action of unknown agents (neurotoxins) to be deduced by the measured cellular response. Using back-propagation ANNs to distinguish neurotoxins under the cascade network, the highest success recognition rate for concentration identification were 96% for peroxynitrite, 88% for rotenone, and 96% for okadaic acid. The recognition rate for neurotoxin identification was 98%. The ANN models required less than ten minutes to train and demonstrated that back-propagation ANNs can be handled by commercially-available computers to train and assimilate neurotoxin impedance information, permitting high success rates in the neurotoxin recognition problems.

Application of Semipermeable Membranes in Glucose Biosensing

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.

Growth of electrodeposited ZnO nanowires

Direct current electrodeposition method was used to deposit zinc oxide (ZnO) nanowire arrays from aqueous zinc chloride in ammonium chloride solution at 70° C onto 10 mm × 10 mm anodic alumina oxide (AAO) templates. The AAO templates featured an average pore diameter of 80 nm. A 40 nm gold layer was sputtered onto the surface of the AAO templates before electrodeposition. ZnO nanowires were grown at a potential of -1V versus Ag/AgCl using DC potential amperometry. Characterization of ZnO nanowires was carried out for the as-deposited nanowire array. Atomic force microscopy was used to study the surface morphology. After deposition for 2.5 hours, the length of the nanowires was approximately 3.58 μm on average. Scanning electron microscopy was used to view the cross-section of as-deposited ZnO nanowire array.