Preparation, characterisation and application of printed medical diagnostic biosensors

Over the past two decades, more accurate, convenient and earlier diagnoses have become a key strategy to reduce health care costs. The application of electronics to biology and medicine has enabled advanced technology of lab-on-a-chip biomedical diagnoses. The aim of this study was to explore possible interface or surfaces which could be printed and utilised to fabricate biosensor for the detection of potential diseases. Overall, the research work was carried out into two dimensions, and therefore, this thesis has been divided into two major sections. The first section (Chapters 1-3) comprises studies carried out on Quantum Tunnelling Composite (QTC) vapour sensors for the detection of potential biomarkers acetone and ammonia in breath. Recent developments in gas-sensing technology and pattern recognition methods made electronic nose technology an interesting alternative for health care devices. Therefore, initial experiments were carried out to evaluate QTC potential as vapour sensing material for an electronic nose. The second section (Chapters 4-10) comprises design, preparation and characterisation of labelless immunosensors for Neisseria gonorrhoea and Chlamydia trachomatis. Electrochemical impedance spectroscopy (EIS) was employed to investigate detection of analytes via impedimetric transduction. The successful construction of an immunosensor depends on effective immobilising of bio-recognition element onto the transducer surface. Thus, conducting polymers having amine functional groups were developed, utilised and evaluated as a suitable matrix for the covalent entrapment of antibodies. Fragments of antibodies were immobilised onto four different functionalised conducting surfaces which included polyaniline, poly (4-amino methyl) pyridine, polytyramine and 3-amino propyl pyrrole, respectively. Fully fabricated sensors were interrogated against various concentrations of Neisseria gonorrhoea and Chlamydia trachomatis. EIS was used to measure the charge transfer resistance of the sensors across a range of frequencies. These sensors were found to specifically detect the intended analytes with a limit of detection of 102 bacterial particles per ml in general. In addition, scanning electron microscopy was employed to study the surface morphologies of a sensor whereas FTIR spectroscopy was employed for the characterisation of all polymers.