The Development and Optimisation of a Low Cost Optical Chemical Sensing Platform
Orpen, Dylan (2011) The Development and Optimisation of a Low Cost Optical Chemical Sensing Platform. Master of Engineering thesis, Dublin City University.
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With recent improvements in wireless sensor network hardware it is logical there should be a concurrent push to develop the sensors that are compatible in terms of price and performance. Wireless sensor networks are made up of a multitude of low power sensing nodes and are typically deployed in a scatter web configuration. A key concept is that the nodes are so low cost and are spread so densely, that the failure of any one node will not be a cause for great concern. The sensed data collected from wireless sensing networks have advantages over other traditional sensing methods. For example, the accuracy of any one particular node is not critical to the system; however, there must be reproducibility in the data from one node relative to the next. Therefore, when data is compared from multiple nodes one can deduce if the signal is increasing or decreasing and, hence, develop a directional sense to the response. This is something that cannot be achieved using traditional single point grab sampling.
The chemical sensor optimised as part of this project is based on the use of two light emitting diodes (LEDs), as both the light source and photodetector. This light sensor, when coupled with a PET slide coated with a pH sensitive colorimetric dye realises a simple gas sensor. Such setups have been successfully used to detect both acetic acid and ammonia. To date the sensors are already low cost due to their operating principle being based on the use of off the shelf LEDs, but flaws include a lack of reproducibility in sensed data. This is partly due to a reliance on poor manufacturing methods. Such inaccuracies have led to the requirement of an expensive individual node by node calibration.
The goal of this work is to improve the system performance through redesign. This will be accomplished by integration of the device into a flowcell platform, and the automation of the sensor creation process. The redesign of the sensor will improve sensor performance and It is hoped that this will increase accuracy in collected data and also increase the reproducibility of the created sensors. This reproducibility increase will be achieved through this careful control of deposited film thickness, and through the utilization of the highly reproducible inkjet printing process. The enhanced reproducibility between sensors opens the potential of calibration free use.
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