Smart electrochemical sensing system for the real time detection of endocrine disrupting compounds and hormones : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Electronics Engineering at Massey University, Manawatu, New Zealand

Abstract

Presented research work has not only provided a real-time tool to perform week-long chemical and bio-chemical assays in minutes yet, it had been operating as a source of community awareness about the said chemicals that we keep ingesting knowing or unknowingly. Phthalates are the most ubiquitous chemicals that pose a grave danger to the human race due to their extraordinary use as plasticizer in consumer product industry. All contemporary detection methods require high level of skills, expensive equipment and long analysis time as compared to the technique presented in this research work that introduces a real time non-invasive assay. A novel type of silicon substrate based smart interdigital sensor fabricated by employing thin film micro-electromechanical system semiconductor device fabrication technology. Electrochemical Impedance Spectroscopy was used in conjunction with the fabricated sensor to detect hormones and phthalates in deionized water. Various concentrations of phthalates as low as 2 parts per billion to a higher level of 2 parts per million in deionized water were detected distinctively using new planar ID sensor based EIS sensing system. The sensor was functionalized by a self-assembled monolayer of 3-aminopropyltrietoxysilane with embedded molecular imprinted polymer to introduce selectivity for the phthalate molecule. Spectrum analysis algorithm interpreted the experimentally obtained impedance spectra by applying complex nonlinear least square curve fitting in order to obtain electrochemical equivalent circuit and corresponding circuit parameters describing the kinetics of the electrochemical cell. Principal component analysis was applied to deduce the effects of surface immobilized molecular imprinted polymer layer on the evaluated circuit parameters and its electrical response. The results obtained by the testing system were validated using commercially available high performance liquid chromatography diode array detector system.