Phosphorus is needed by living organism including humans and plants, to survive. Imbalance in phosphate concentration in human body can result in numerous diseases or disorders while excess phosphorus levels in water bodies like lakes, and rivers, are responsible for the rise in incidence of algal bloom across world. Current commercial phosphate monitoring systems are dominated by colorimetric measurements while electrochemical sensors including potentiometric, amperometric and voltammetric sensors are still in the research phase. Electrochemical sensors require stable reference electrodes for reliable measurements that pose challenges for miniaturization. Solid state potentiometric sensors are widely explored due to their rapid response, easy fabrication and simple electronic measurement system. However, the sensor miniaturization is dependent both on the working and reference electrode. Metal electrodes like cobalt offers advantages such as reagent-free detection, easy to miniaturize but the sensitivity of zero-current potentiometric sensors is limited by the theoretical Nernstian limit and cobalt sensors also require chemical pretreatment in standard solution before measurement. Here, an in situ electrical pretreatment method is proposed to eliminate the need of chemical pretreatment and enhance the sensitivity of cobalt electrodes to -91.4 mV/ decade of phosphate concentration. However, this electrode still needs a reference electrode for reliable measurements. Therefore, this study has demonstrated a chemiresistive sensing platform for solid state detection of phosphate using both enzyme and enzyme-free methods. A rapid prototyping method was developed to pattern the thin metal films (~100 nm thickness) using a bench top plotter cutter. The method was used to fabricate thin gold film contact electrodes for chemiresistors. The thin gold leaf contact electrodes exhibited low-noise and offered a robust, rapid and reproducible manufacturing process for chemiresistors. The chemiresistive sensor showed a wide measuring range (0.5 ppm to 500 ppm) for hydrogen peroxide detection. The sensor was deposited with glucose oxidase to demonstrate the application of the sensor for peroxidase assays to detect glucose in standard buffer solution and human pooled plasma. Phosphate also is detected using pyruvate oxidase in presence of pyruvate to generate hydrogen peroxide as the detectable molecule. Finally, metal phthalocyanines were used to perform enzyme-free phosphate measurements. This work demonstrated the sensor technologies which could be used for in-field phosphate monitoring to prevent algal bloom and it also provides phosphate monitoring methods for rapid detection in medical diagnostics for early diagnosis for diseases like chronic kidney disease and to improve the patient’s outcomes for such diseases. / Thesis / Doctor of Philosophy (PhD) / Phosphorus is an essential element for the survival of living beings including humans and plants because it is needed in multiple physiological pathways and functions like cellular signalling, energy storage, metabolism and maintenance. Therefore, phosphate in the human body is strictly regulated and in disease conditions like chronic kidney disease, and metabolic disorders. It can increase or decrease resulting in ailments and worsening of diseases. Phosphorus is also extensively used in the agricultural field to improve the growth and crop yield. Excess phosphorus from these fertilizers can enter our water sources via agricultural water run-offs leading to the increasing incidences of algal bloom across world. Current phosphorus measuring systems require chemicals which generates toxic waste, needs manual sample collection and transport, and have narrow measuring ranges. There is an urgent need for sensors which would eliminate the need of sample collection and processing, do not require toxic chemicals and could work over a wide detection range. This study presents two solid-state sensor technologies which would simplify the phosphate detection for both environmental and medical diagnostics samples.

While the active dynamic stability of automobiles has increased over the past 17 years there have been very few similar advances made with electrically powered wheelchairs. This lack of improvement has led to a long standing acceptance of less-than-optimal stability and control of these wheelchairs. Accidents due to loss of stability are well documented. Hence, the healthcare industry has made several efforts for improved control of electric powered wheelchairs (EPWs) to provide enhanced comfort, safety and manoeuvrability at a lower cost. In response, an area of stability control was identified that could benefit from a feedback control system using solid state sensors. To design an effective closed–loop feedback controller with optimal performance to overcome instabilities, an accurate model of wheelchair dynamics needed to be created. Such a model can be employed to test various controllers quickly and repeatedly, without the difficulties of physically setting a wheelchair up for each test. This task was one central goal of this research. A wireless test-bed of a front wheel drive (FWD) wheelchair was also developed to validate a dynamic wheelchair model. It integrates sensors, a data control system, an embedded controller, and the motorised mechanical system. The wireless communication ensures the integrity of sensor data collected and control signals sent. The test-bed developed not only facilitates the development of feedback controllers of motorised wheelchairs, but the collected data can also be used to confirm theories of causes of dynamic instabilities. The prototype test-bed performed the required tasks to satisfaction as defined by the sponsor. Data collected from live tests in which the test-bed followed set patterns, was processed and analysed. The patterns were designed to induce instability. The analysis revealed that an occupied wheelchair is more stable than an unoccupied wheelchair, disproving an initial instability theory proposed in this research. However, a proximal theory explaining over-steer is confirmed. Two models of the FWD test-bed were created. First, a dynamic model inherited from prior research, based on equations of motion was tested and enhanced based on measured data. However, even with alterations to correct parameter values and variables in the equations, a complete model validation was not possible. Second, a kinematic model was created with a factor to compensate for dynamics not normally accounted in kinematic models. The kinematic model was partially validated versus the measured data. Although, still highly accurate, there is room for improvement in this model. Both models contained a sub-system drive motor model, to account for input forces to the FWD wheelchair system model, which is fully validated.