Document Type

Doctoral Thesis

Disciplines

1.3 PHYSICAL SCIENCES, Optics, 2.2 ELECTRICAL, ELECTRONIC, INFORMATION ENGINEERING, 3.3 HEALTH SCIENCES

Publication Details

A thesis submitted for the degree of Doctor of Philosophy to Technological University Dublin, 2025.

doi:10.21427/7y5p-j980

Abstract

From aerospace to agriculture, sensors play a fundamental role in many aspects of modern life. Sensors form an integral part of the complex systems and devices required for the continued functioning and development of services and industries across society. The use of sensors is paramount in areas affecting human health, one such area being the monitoring of indoor air quality, in particular the detection of volatile organic compounds (VOCs). Human contact with VOCs has been associated with many health complications, including skin and eye irritation, cardiovascular damage, and cancers. Optical, electrical, gravimetric, and chemical sensors have been developed for VOC detection, but significant challenges remain present, in particular with obtaining high sensitivity and selectivity with a low-cost, simple-to-use device. The primary objective of this work was to develop holographic-based optomechanical sensors for VOCs. Holographic sensors have been demonstrated previously to be effective in the detection of many analytes, including VOCs. While presenting many advantages, such as low cost, simple fabrication and readout techniques, and electromagnetic insensitivity, further work is required to enhance the sensitivity and selectivity of these devices to compete with the detection limits of the current state-of-the-art commercial VOC detectors. This work aims to enhance the sensitivity of holographic sensing devices by examining the coupling of a holographic sensor with a mechanical transducer – initially through a bilayer cantilever structure and ultimately using a holographic membrane, and by varying the holographic structure – diffraction grating and lens. Such an approach could lead to low-cost, easy-tooperate, highly sensitive devices for indoor air monitoring. The work presented can be summarised in three main sections: 1) modelling, design, and fabrication of a bilayer optomechanical holographic cantilever sensor – the model representing a novel step in simulating the optomechanical coupling; 2) testing of the cantilever device for sensitivity ii to VOCs and comparison with traditional fixed holographic sensors and 3) design, fabrication and testing of a holographic lens membrane for enhanced VOC sensitivity. The sensors are primarily tested for their response to ethanol, but butanol, xylene and toluene are also examined to assess the selectivity of the devices. The work demonstrates, through several novel steps, the benefits of optomechanical coupling, which results in an approximately 10-fold increase in sensitivity. While further steps are required to achieve improved selectivity through functionalizing the photopolymer material with zeolite and metal-organic framework (MOF) nanoparticles, likely necessitating the use of a sensing array, in sum, the work represents a significant step forward in the development of holographic sensors for VOCs and their implementation in day-to-day real-world applications.

DOI

https://doi.org/10.21427/7y5p-j980

Creative Commons License

Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.

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