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Novel applications of colourimetric gas sensors Lauren Rose McDonnell (24304511) PUREID: 674325279 CO2 indicator optical sensor photography micro-respirometry H2 indicator TVC aquarium environmental monitoring bacteria anaerobes O2 sensor This thesis is focused on developing new applications of existing and novel colourimetric indicators, primarily for the detection of carbon dioxide (CO₂). <br><br>The Introduction chapter gives a short history of CO₂ indicators from aqueous solutions, to ‘dry’ ink-based indicators, and the onset of plastic films. Some existing applications of colourimetric CO₂ indicators are discussed. <br><br>The Experimental chapter outlines the most important instrumentation and methods used throughout this PhD, to include UV-Vis spectroscopy, photography and digital colour analysis (DCA), lifetime O₂monitoring, microbiological techniques, general plastic film CO₂ indicator preparation, and gas mixing.<br><br>In Chapter 3, two commercial colourimetric CO₂ indicators are replicated in the lab- one for monitoring the level of dissolved CO₂ in an aquarium, and another for monitoring the level of CO₂ in breath. Photography and DCA are used to convert the colour data from the indicators into a quantitative measure of CO₂.<br><br>In Chapter 4 the preparation of a plastic film indicator for the measurement of CO₂ in aquaria is described, based on extrusion of low-density polyethylene (LDPE) mixed with a small amount of a CO₂ sensitive pigment. The pigment comprises a mixture of a pH-indicator dye, xylenol blue (XB), with a base, coated onto silica. Digital photography and DCA quantifies the response of the XB-LDPE indicator in an aquarium.<br><br>In Chapter 5, a new form of micro-respirometry, %CO2-μR, is used to measure total viable count (TVC) of bacteria. In %CO₂-μR, the apparent absorbance of a small, XB-LDPE 3D-printed CO₂ indicator is measured at any <i>t</i>, as it is related to the %CO₂ dissolved in inoculated growth medium. The potential of %CO₂-μR for measuring the bacterial load of CO₂-generating aerobes and anaerobes is studied and discussed briefly. <br><br>Finally, a colourimetric indicator for the detection of microbial hydrogen (H₂) evolution is described in Chapter 6. A H₂-sensitive indicator was fabricated based on the dye methylene blue (MB), and was used to determine the TVC of a range of H2-producing anaerobes. <br> 2026-10-01T16:09:29Z Text Thesis 10.17034/32826260.v1 https://figshare.com/articles/thesis/Novel_applications_of_colourimetric_gas_sensors/32826260 All Rights Reserved