Title:
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Test and condition monitoring technologies for bio-fluidic microsystems
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Lab-on-chip devices and bio-fluidic microsystems are emerging technologies that exhibit
the required fluidic transport, bio chemical detection and control functions to enhance the
detection resolution and accuracy within a single miniaturised portable instrument for
bio-diagnostic and bio-synthesis applications. These devices impact a number of markets,
including medical diagnostics, pharmacology, environmental monitoring and industrial
control. Example applications are DNA extraction from blood and detection of pathogens
or genetically modified organisms. Electrode technology is fundamental to numerous
actuation and sensing functions within these microsystems. Reliability is a key
component of these microsystems and most applications require extremely low
probabilities of false positives or negatives. New methods of validating the functionality
and integrity of measurements are hence required. Embedded test and condition
monitoring are crucial technologies for delivering these capabilities. This thesis makes
significant contributions to knowledge in these areas to further the development and
viability of accurate test equipment.
The work in this thesis focuses on delivering novel solutions and methodologies that can
be used to increase the reliability of electrode-based bio-fluidic mi'crosystems and cellbased
biosensors. Three self-test solutions have been developed to address surface
degradation within the sensing interface of a cell-based biosensor system and microfluidic
chips. The first solution, a mid-frequency oscillation test approach, is based on the
sensitivity of the interface capacitance to degradation, contamination and fouling. The
second solution proposes a new fault diagnosis approach using an Artificial Neural
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Abstract
Network for detecting degradation in electrodes that interface to fluidic or biological
systems. The third solution studies the feasibility of scanning the strength of a test signal
over an array of electrodes to monitor degradation. The design of the monitoring
structures has been validated through physical characterisation involving data extracted
for both a single electrode and an array of electrodes where a micro controller, an
analogue multiplexer, a test circuit, and an LeD have been used to achieve a real-time
condition monitoring system. The novel test techniques provide analogue values directly
related to the degradation of the electrode, so have the ability to provide accurate on-line
degradation detection for a range of conditions across the electrode surface.
Optimising the design of the microfluidic chips to maximise flow rate and the
investigation into new methods for validating functionality and integrity of the readings
have also been studied numerically. In addition, this thesis concretely examines potential
research directions for future bio-fluidic microsystems.
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