Abstract:
The purpose of this thesis is to develop a rapid, sensitive and selective optical sensor
for Campylobacter jejuni detection as it is the most common cause of foodborne
illness in humans. The optical sensor platform was based on the optical fibre long
period grating (LPG). The LPG fabrication technique chosen was the point-by-point
method, involving the UV irradiation of photosensitive doped optical fibre. This
technique allows the tailoring of the sensor platform to the requirements of the
application. Polyclonal antibodies were selected as the material which can selectively
immobilise bacterial cells on to the surface of the fibre optic. Methodologies for
reliable and repeatable coating of this material (antibodies) onto the surface of the
sensor platform were developed. Two methods to integrate the antibodies to the
surface of the fibre, adsorption and covalent binding, were explored. Bovine serum
albumin was selected as the material to block the sites on the surface of the fibre
not covered by the antibodies, with the aim to prevent non-specific adsorption. The
sensor was tested in a direct assay using bacterial samples at different concentrations.
The sensitivity of the sensor was evaluated using different concentrations of the target
bacteria in a direct assay and multiple repetitions, achieving a limit of detection of
10⁴ and 10³ CFU/mL (colony-forming unit (CFU), a measure of viable cells in a
sample) for the sensor created using adsorption and covalent binding of antibodies,
respectively. The selectivity of the sensor was explored by testing the sensor against
different bacteria in a direct assay and multiple repetitions. The response of the
sensor was 100% for Campylobacter jejuni (target bacteria), 22.77% for Listeria
monocytogenes, 9.47% for Salmonella typhimurium and 3.01% for Escherichia coli.
The enhancement of the sensitivity of the sensor using cell staining was explored.
Cell staining induces a change in the refractive index of the cell, enhancing the
signal detected, improving the limit of detection by one order of magnitude to 10²
CFU/mL.
