Abstract:
This PhD project was funded by the European Union Framework 6 ELISHA
programme as part of the ELISHA programme. The aim of the research was focused
towards the development of point-of-care, simple, cost-efficient and reliable
impedimetric immunosensors for the rapid detection of important antigens such as
ciprofloxacin and digoxin. Through the cooperation of the 9 involved partners a
number of protocols have been developed for sensor fabrication and sample testing
that allow both rapid and reliable detection of a range of antigens. This work
describes in depth, the use of polymers and cyclic voltammetry for electrode surface
modification, the use of the avidin-biotin system for antibody immobilisation and
finally the use of Electrochemical Impedance Spectroscopy for antigen detection. We
report here the successful development of electrochemical impedimetric carbon based
immunosensors for the detection of free-form and chelated ciprofloxacin (both in
laboratory buffer and milk), digoxin and green fluorescent protein. It was observed
during this work that unavailability of sufficient quantities of the monoclonal
antibodies could lead to early sensor saturation and hence a less extended antigen
detection range, while very low quantities of immobilised antibodies could also give
rise to erroneous results. The immunosensors towards ciprofloxacin detected the
respective antigen when this was present between 1 ng ml-1 and 10 μg ml-1 in PBS
buffer and 0.1 ng ml-1 to 10 μg ml-1 when the antigen was added to milk samples. The
developed digoxin immunosensors could detect digoxin between the concentrations of
0.1 ng ml-1 and 10 μg ml-1. Lower detection limits where observed for the sensors
targeting GFP which could detect their respective antigen at concentrations as low as
100 pg ml-1. The tested concentration range of the latter sensors was extended up to
100 ng ml-1.
