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Mid-Infrared Integrated Devices for Optical Chemical Sensing
The mid-infrared (MIR) spectral range is of special interest for establishing optical chemical sensor technologies by allowing specific molecular identification and quantification, whether the sample is in a liquid, gas or solid form, in addition to providing highly sensitive, rapid, reagent-free and non-destructive detection.
This thesis explores four different liquid- and gas- sensing applications and methods using MIR spectroscopy by integrating it with other technologies, such as microfluidics and fibre-optics.
Firstly, fibre-optic integrated microfluidic devices were developed and tested for con- tinuous fluid monitoring. These showed good sensing capabilities for online, continuous and real-time liquid sensing in hard-to-reach locations.
Next, this thesis presents the establishment and clinical testing of a novel method for continuous monitoring of the brain chemistry of traumatically brain-injured patients by MIR transmission spectroscopy. Here, the outlet of a cerebral microdialysis catheter is cou- pled to a micro flow-cell and the flowing microdialysate is continuously analysed. Clinical studies were carried out and showed the capability of this system for performing continuous patient monitoring over several hours. With further optimisation, the implementation of this system could lead to improved patient outcome.
This thesis also presents a novel method and system based on MIR fibre-optic evanescent- wave spectroscopy, which enables enhanced detection of volatile organic compounds (VOCs). Here, a nanoporous silicon cladding was used to reversibly concentrate molecules close to the fibre surface, thus enhancing VOC detection. A significant increase in sen- sitivity was seen compared to that of an uncoated fibre and successful detection of three different VOCs, both independently and in binary mixtures, was achieved.
Finally, this thesis introduces a simple and relatively low-cost fibre-optic sensor for in-line, real-time bioprocess monitoring. The sensor was successfully able to monitor varying concentrations of product (sophorolipids) in fermentation broth and was able to distinguish between the two types of generated product (acidic and lactonic sophorolipids).
The work presented in this thesis showed that MIR-integrated sensors have great potential to provide novel and/or enhanced sensing solutions in a wide range of applications, including medical, industrial and environmental
Assessment of a Microfluidic Intravenous Oxygen Generating Platform to Aid Acute Respiratory Failure
Acute respiratory failure is associated with a high mortality rate, despite the advances in
conventional treatments.
This work presents the development of a proof-of-concept device for assessing the viability of an
oxygen-generating catheter, deployed intravenously, to temporarily sustain a patient who is suffering
from acute respiratory failure. The assessment device mimics the interface between the catheter and
bloodstream (deoxygenated water substitutes the blood), and consists of two parallel channels
separated from each other by an oxygen-permeable membrane that simulates the catheter material.
Several polydimethylsiloxane membranes with enhanced permeability were developed and tested on
the device according to their permeation rates.
The highest permeation rate achieved was 3.6×10-7 cm3/s (equivalent in-blood value) considering
the device’s surface area and applied pressure. However, the extrapolation of this value to a catheter
with increased surface area demonstrated a predicted oxygen permeation rate of 1.6×10-3 cm3/s.
Although the oxygen permeation rates achieved here do not yet reach the minimum required rate to
sustain a patient with only 30 % of their lungs functional (1.6 cm3/s O2), it may be enhanced further
by improving certain parameters such as material permeability, surface area and applied pressure.
The ability to administer oxygen or other gases directly into the bloodstream may portray a
technique for short-term rescue of severely hypoxemic patients to increase whole body or at-risk
organ oxygenation