H. Troy Nagle

Flexible (Kapton-based) microsensor arrays of high stability for cardiovascular applications

The design, fabrication and performance characteristics of Kapton-based planar mini and semimicro potentiometric sensors with an Ag/AgCl or a quinhydrone-based redox internal reference electrode are described. The ion-selective membranes cast from conventional and various modified PVC matrices and containing different pH-sensitive ionophores are ranked on the basis of their performances in hostile environments. The adhesive bonding strength of the different PVC membranes to the polyimide-coated Kapton substrate was quantitatively evaluated as a function of fabrication procedure and sample solution contact. The long-term stability of the electrodes was characterized by the alterations of the analytical parameters of the sensors over a period of time, as well as by determining the resistance changes of their sensing membranes.

Transient response analysis of an electronic nose using multi-exponential models

Abstract The purpose of this study is to model the transient response of conductivity-based gas sensors in the context of odor recognition with an electronic nose. Commonly, only the steady-state response of the sensor is used for pattern recognition, ignoring the transient response, which conveys useful discriminatory information. The transient response is modeled as a sum of real exponential functions that represent the different decay processes that occur during sampling of the gas into the sensor chamber and adsorption of the odor compounds onto the sensing element. Four multi-exponential models are reviewed: Gardner transform, multi-exponential transient spectroscopy, Pade-Laplace and Pade-Z transforms. Validation on experimental data from an array of conducting-polymer gas sensors shows that the Pade-Laplace and Pade-Z models have better resolution capabilities than the two spectral transforms.

An implantable radiation dosimeter for use in external beam radiation therapy

An implantable radiation dosimeter for use with external beam therapy has been developed and tested both in vitro and in canines. The device uses a MOSFET dosimeter and is polled telemetrically every day during the course of therapy. The device is designed for permanent implantation and also acts as a radiographic fiducial marker. Ten dogs (companion animals) that presented with spontaneous, malignant tumors were enrolled in the study and received an implant in the tumor CTV. Three dogs received an additional implant in collateral normal tissue. Radiation therapy plans were created for the animals and they were treated with roughly 300 cGy daily fractions until completion of the prescribed cumulative dose. The primary endpoints of the study were to record any adverse events due to sensor placement and to monitor any movement away from the point of placement. No adverse events were recorded. Unacceptable device migration was experienced in two subjects and a retention mechanism was developed to prevent movement in the future. Daily dose readings were successfully acquired in all subjects. A rigorous in vitro calibration methodology has been developed to ensure that the implanted devices maintain an accuracy of +/-3.5% relative to an ionization chamber standard. The authors believe that an implantable radiation dosimeter is a practical and powerful tool that fosters individualized patient QA on a daily basis.

In vivo and in vitro testing of microelectronically fabricated planar sensors designed for applications in cardiology

SummaryIon-sensitive, planar micro-electrode arrays were fabricated by photolithographic microelectronics technology on a flexible polyimide substrate. The steps of the microelectronics processing are summarized. The electrodes were tested in blood serum, whole blood and in the hamstring muscle of anesthetized rabbits. The performance characteristics of planar pH-sensors are compared with commercial glass electrodes. The close correlation of the data are encouraging for further acute and later chronic applications.

Quantitative Characterization of Epicardial Wave Fronts During Regional Ischemia and Elevated Extracellular Potassium Ion Concentration

AbstractThis study applied zero-delay wave number spectral estimation as a means of quantifying the changes in activation and recovery sequences of propagating plane waves on the epicardial surface of in situ porcine hearts during regional hyperkalemia and ischemia. Unipolar electrograms (104) were recorded from the left ventricular surface of nine hearts using a plaque electrode array with 1 mm spatial sampling intervals. The objectives were (1) to define a set of parameters capable of quantifying the spatial and temporal changes in measured extracellular potentials associated with localized ischemia prior to the onset of conduction block; (2) to elevate regional levels of extracellular potassium ion concentration and quantify potential changes due to this known physiologic manipulation; and (3) to use quantitative parameters to make statistical comparisons in order to distinguish wave fronts during normal, ischemic and hyperkalemic conditions. Results showed that the parameters of wave number and average temporal frequency and the associated power, as determined from the wave number spectrum, provided statistically significant (p < 0.05) quantification of changes in wave front features during normal and ischemic or hyperkalemic conditions. The results were consistent with results obtained from conventional time–space domain methods like isochronal mapping and electrograms, with the advantage of a quantitative result enabling simple comparisons and trend analysis for large numbers of heart beats.

Flexible electrode array for retinal stimulation

The retina interfacing and prosthesis project is a joint project between the Duke University Eye Center, NC State University, University of NC, and the Research Triangle Institute. The ultimate goal of the project is to design, build, and test a retinal prosthesis that would capture photons, electrically stimulate the retina, and thus generate a phosphene map (focal flashes of light) that would provide information about movement, light intensities, and edge detection to otherwise severely visually handicapped patients. This paper summarizes the design and fabrication of a flexible, biocompatible stimulating array to be connected to a photosensing chip with image processing capabilities.

Environmental pollutants alter taste responses in the gerbil

Taste and smell are chemical senses that play a crucial role in food selection. Damage to taste and smell receptors can impair food intake, nutritional status, and survival. The purpose of this study was to determine the effects of 11 environmental pollutants (nine insecticides and two herbicides) on electrophysiological taste responses in the gerbil. Integrated chorda tympani (CT) recordings were obtained from gerbils to a range of tastants before and after a 4-min application of 1 of 11 environmental pollutants. The taste stimuli were: sodium chloride (100 mM), calcium chloride (300 mM), magnesium chloride (100 mM), HCl (10 mM), potassium chloride (500 mM), monosodium glutamate (MSG) (50 mM), sucrose (100 mM), fructose (300 mM), sodium saccharin (10 mM), quinine HCl (30 mM), and urea (2 M). The nine insecticides included organophosphorous, carbamate, and pyrethroid insecticides. The seven organophosphorous insecticides tested were: acephate, carbofuran, chlorpyrifos, chlorpyrifos oxon, demeton, malathion, and methamidophos. The carbamate insecticide carbaryl and the pyrethroid insecticide fenvalerate were also tested. Two herbicides, paraquat and glyphosate, were tested, and dose-response curves for each of these two herbicides were also determined. All of the 11 insecticides and herbicides had an effect on some of the taste stimuli tested. Application of 10 mM methamidophos exhibited the greatest amount of suppression on the 11 taste solutions. Each taste stimulus was significantly suppressed with the exception of 2 M urea. Herbicides paraquat and glyphosate also reduced responses to several tastants. These data indicate that environmental pollutants can modify taste responses in the gerbil.

Odor Assessment of Automobile Cabin Air With Field Asymmetric Ion Mobility Spectrometry and Photoionization Detection

Odor quality in the cabin air of automobiles can be a significant factor in the decision to purchase a vehicle and the overall customer satisfaction with the vehicle over time. A current standard practice uses a human panel to rate the vehicle cabin odors on intensity, irritation, and pleasantness. However, human panels are expensive, time-consuming, and complicated to administer. To address this issue, we present a machine olfaction approach to assess odors inside automobiles. The approach uses a field asymmetric ion mobility spectrometer and a photoionization detector to measure volatile organic compounds, and a multivariate technique to map sensor data into human ratings. Validation on an experimental dataset of odors from ten different vehicles shows a correlation (0.67-0.84) between model predictions and ground truth from a trained human panel. These results support the feasibility of replacing human panel assessments by objective instrumental means for quality control tasks in the production process.

An Evaluation of Department Head Performance

This paper describes the performance evaluation of the Department Head used by the senior Electrical Engineering Faculty at Auburn University during the last two years.

Standard analytes for E-noses and E-tongues

Odor and taste compounds are suggested here as standard analytes for e-nose and e-tongue instruments to provide performance criteria regarding the capacity of these electronic sensing devices to mimic human chemosensory responses. Representative odor and taste standards for sensitivity, suprathreshold intensity, and quality are proposed. Ultimately, a formal set of analytical standards should be established by the electronic sensing community. Subsets of these formalized standards could then be adopted for specific applications.