Edric I. Gill

Review on State-of-the-art in Polymer Based pH Sensors

This paper reviews current state-of-the-art methods of measuring pH levels that are based on polymer materials. These include polymer-coated fibre optic sensors, devices with electrodes modified with pH-sensitive polymers, fluorescent pH indicators, potentiometric pH sensors as well as sensors that use combinatory approach for ion concentration monitoring.

Review Paper: Materials and Techniques for In Vivo pH Monitoring

Advances in semiconductor sensor technology, medical diagnostics, and health care needs a rapid boost in research into novel miniaturized pH sensors, which can be used in vivo for continuous patient monitoring. Requirements for the in vivo sensor are materials biocompatibility, high measurement precision, a response time of an order of less than seconds, and the possibility of continuous 24-h monitoring. Monitoring of the pH values is important in the study of tissue metabolism, in neurophysiology, cancer diagnostics, and so forth. Muscle pH can be used to triage and help treat trauma victims as well as to indicate poor peripheral blood flow in diabetic patients. Clearly, to avoid infection and spread of diseases, all in vivo monitoring devices should be single-use/disposable, which puts strict requirement on their price. This paper reviews the wide range of methods and materials used for in vivo measurement of pH levels, such as using the optical fibers, pH-sensitive polymers, ion-sensitive field effect transistors, near infrared spectroscopy, nuclear magnetic resonance, and fluorescent pH indicators.

pH Sensitivity of Novel PANI/PVB/PS3 Composite Films.

This paper reports on the results from the investigation into the pH sensitivity of novel PANI/PVB/PS3 composite films. The conductimetric sensing mode was chosen as it is one of the most promising alternatives to the mainstream pH-sensing methods and it is the least investigated due to the popularity of other approaches. The films were deposited using both screen-printing and a drop-coating method. It was found that the best response to pH was obtained from the screen-printed thick films, which demonstrated a change in conductance by as much as three orders of magnitude over the pH range pH2-pH11. The devices exhibited a stable response over 96 hours of operation. Several films were immersed in buffer solutions of different pH values for 96 hours and these were then investigated using XPS. The resulting N 1s spectra for the various films confirmed that the change in conductance was due to deprotonation of the PANI polymer backbone. SEM and Profilometry were also undertaken and showed that no considerable changes in the morphology of the films took place and that the films did not swell or contract due to exposure to test solutions.

Investigation of Thick-Film Polyaniline-Based Conductimetric pH Sensors for Medical Applications

This paper reports on the development and testing of a polyaniline-based conductimetric pH sensor. The sensor functions successfully in both the pH range for stomach acid (pH1.0-pH2.0) and for human blood (pH7.0-pH8.0). Experiments were performed by exposing the sensors to buffer solutions with pH values in the ranges identified. The sensors demonstrated reproducible and repeatable results with little hysteresis being recorded between experiments, along with a response time of approximately 1 min in acidic solutions and 2 min in buffers with pH values in the blood pH range. In the case of measurements made in the blood pH range, a novel memory effect was observed, which corresponds to a permanent ldquorecordingrdquo of the pH measurement into the electrical characteristics of the film. This memory effect only applies to measurements made in alkaline pH ranges and is due to the deprotonation of the polyaniline material in the sensing layer. The sensor reported in this paper has the potential to be a more economically viable option when compared to other approaches being used for commercial applications.

Drop-Coated Polyaniline Composite Conductimetric pH Sensors

This work describes the fabrication and development of a polyaniline based conductimetric pH sensor. Two types of drop coated polyaniline films were investigated and it was found that the undoped emeraldine base polyaniline produces the best electrical response to pH. The results obtained show that the lowest conductance of these films occurs at the lowest pH value (pH2), with the conductance increasing with increasing pH. It is thought that this response is due to effects from the polymer binder, which is used to increase adhesion between the pH-sensitive film and the substrate.

Microsensors Arrays Manufacture Using the NanoeNablerTM

Novel method for microarrays manufacture using BioForce NanoeNablertrade was successfully employed for developing sensors for biomedical applications, namely pH and glucose monitoring. It is envisaged that findings of this work would form the basis for miniaturised diagnostic system for a wide range of applications.

Gamma Radiation Sensing Using ZnO and SnO2 Thick Film Interdigitated Capacitors

A novel cost-effective real-time gamma radiation monitoring system based on metal oxide thick films was designed and tested. The changes in capacitances of ZnO and SnO2 thick film capacitors with interdigitated electrodes were monitored in real time under the influence of gamma radiation using miniaturized, low power, bi-directional wireless communication system. The capacitive interface circuitry was based on a Delta-sigma (SigmaDelta) modulator using switched capacitor (SC) circuit architecture with integrated on-chip temperature sensor. At the base station side, an frequency shift keying (FSK) receiver/transmitter is connected to another MCU unit, which send the received data or received instructions from a PC through a graphical user interface GUI. Industrial, scientific and medical (ISM) band RF (433 MHz) was used to achieve half duplex communication between the two sides. All the modules of the mixed signal system are integrated in a printed circuit board (PCB) of size 22.46times20.168 mm. The overall system supply voltage is 2.7 V maximum. 137Cs source with an activity of 370 kBq was used. An increase in the values of capacitance with radiation was recorded for both films to a certain dose level, determined by the material of sensitive layer.

Novel Conducting Polymer Composite pH Sensors for Medical Applications

Sensors for pH measurements in the pH range of human blood (pH7.0-pH8.0) is reported. The sensors comprise of a gold interdigitated electrode structure with a novel polyaniline-based composite thick film as the sensing layer. The sensors showed a sensitivity of approximately 10 Ω/pH unit, when in contact with the test solutions. Due to the permanent effects of the pH of the solution on the films, the resistance of the films (after removal from the solution) varied over several orders of magnitude. The sensors demonstrated a repeatable response.

Polymer Based Micro Sensors Arrays for Ph and Glucose Monitoring

Novel method of manufacturing micro sensors arrays for biomedical applications using BioForce NanoeNablerTM is reported. The operation of pH and glucose sensing elements is based on the properties of polymers, which exhibit a change in their electrical characteristics (such as resistance or capacitance) on exposure to solutions with different concentrations of pH or glucose. A sensor for glucose was successfully fabricated using the enzyme glucose oxidase immobilized within the polymer poly (o-phenylenediamine). This sensor was then successfully miniaturized utilizing immobilization for a dry process. The concentrations used for the microsensor were between 1 mM and 6 mM. Samples containing different concentrations of glucose were applied to the sensor while the system was being monitored for variances in either current or conductance. The resulting changes in the electrical characteristics of the sensor monitored in real time were found to be proportional to the different concentrations of glucose applied. Microscaled interdigitated electrodes were used for sensors array, with 48 sensors places on one chip. It is envisaged that findings of this work would form the basis for miniaturised point-of-care diagnostic system.

Nanopatterning of micro sensor arrays for pH monitoring

There is a need for accurate and instant measurement of pH values in a wide range of applications. The research on miniaturized polymer based pH sensors has recently emerged due to the progress made in polymer materials science. Novel method of manufacturing micro sensors arrays for biomedical applications using BioForce NanoeNablerTM is reported. This nanopatterning system uses a liquid dispensing process via specially designed surface patterning tool (SPT), which is microfabricated cantilever with an integrated passive microfluidic system. During the deposition process, which typically takes less than 100 msec, SPT end touches the surface and a volume of fluid is instantly transferred. The NanoeNablerTM can deliver attoliter to picoliter volumes of liquid with a high degree of spatial accuracy, which resulted in sensor heads measuring 1-2.5 μm to 30 μm. These sensors were developed for biomedical applications, in particular pH monitoring. It is envisaged that findings of this work would form the basis for miniaturised point-of-care diagnostic system. The operation of the sensing elements is based on the properties of polymers, which exhibit a change in their electrical characteristics (such as resistance or capacitance) on exposure to solutions with different concentrations of pH value.