Functionalised surfaces for bacterial discrimination

Abstract: Bacterial detection and identification is a critical step in many arenas, including food and water safety, clinical diagnostics, bioprocess control and biosecurity. Social hygiene has a direct correlation with the strict control of microorganisms in these fields. The worldwide cases of bacterial infectious disease is assessed to be 1-2 billion annually, and these have a massive negative effect on the global economy. Although many precise techniques are currently available, a huge mortality and morbidity related to bacterial infection disease continues to be reported annually due to misdiagnosis or delay in diagnosis. Increasing efficiency and reliability of pathogen detection methods will potentially improve social health and protect society against pathogenic diseases.The development of culture media for selective isolation and differentiation of bacteria started in the late 19th century. Immunological assays and then genotyping techniques were developed in 20th century, in addition to many less commonly used techniques for bacterial detection. Each of the currently used methods has its advantages and weaknesses in terms of speed, cost and accuracy. Much effort has recently been devoted to developing biosensors for bacterial detection for simpler and more rapid use.This thesis is focused on functionalised surfaces for the development of biosensors for bacterial discrimination and detection, and is divided in three subsections. First, we explored a new approach for bacterial discrimination based on pattern recognition. Traditional culturing methods discriminate bacteria based on their metabolic activity pattern. Taking inspiration from the extensive body of work that reports the use of electronic-noses to differentiate bacteria based on the volatiles patterns they produce, we explored the possibility of bacteria differentiation based on adhesion patterns. By altering the electropolymerisation conditions, the physicalchemical surface properties of polypyrrole (PPy) can be tuned to fabricate a range of dissimilar surfaces. The adhesion of different bacteria on a series of polymers was measured. Data analysis of the adhesion patterns proved that bacteria can be discriminated by examining their adhesion to dissimilar surfaces. Next, we developed a new functionalisation of PPy by doping PPy with 4-N-Pentylphenylboronic Acid and investigated the modulation of bacteria binding to those surfaces. In this second section, a new electropolymerisation technique for whole-cell imprinting was developed based on different functional monomers. 3-Aminophenyl boronic acid was shown to be a good monomer to produce whole-cell imprinted polymers (CIP) with high affinity for bacterial cells with improved releasing ability. Finally, in the third section aptamers, which are promising synthetic recognition elements, were explored for bacterial detection testing. A specific aptamer was used to fabricate of a prototype of label-free aptasensor for bacterial detection. Also, the SELEX process was used to produce a pool of aptamers, or “polyclonal” aptamers, which targeted a group of bacteria species. Using polyclonal aptamers as a recognition element enables biosensors to enhance their resolution to detect broader types of bacterial species using a single serological-like test.