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The objective of this thesis is to quantitatively detect ochratoxin A (OTA) in Canadian grain by electrochemistry. To this end, two distinct sensing approaches were developed. In the first approach, a simple label-free sensor was designed to detect OTA. The oxidation mechanism of OTA was investigated using cyclic voltammetry (CV), and the impact of pH on the sensor's response to OTA was explored. Experimental design techniques were employed to optimize the analytical signal. OTA was successfully detected in wheat extracts using differential pulse voltammetry (DPV). The calculated analytical limit of detection (LOD) and limit of quantification (LOQ) were 57.2 nM and 190.6 nM, respectively. For the second approach, a gold electrode (GE) was modified with an OTA-specific aptamer to create a selective aptasensor. Methylene blue (MB) was linked to the aptamer, and the cathodic peak resulting from the reduction of MB at the aptasensor's surface was recorded as the analytical signal using square wave voltammetry (SWV). The surface packing density of the sensor was calculated to optimize the OTA aptamer concentration during sensor modification. The proposed aptasensor detected OTA in phosphate-buffered saline (PBS) media with a lowest measurable concentration (LMC) of 3.44 µM and a lowest quantifiable concentration (LQC) of 10.42 µM. The aptasensor demonstrated its capability to detect OTA in spiked wheat extracts with acceptable accuracy. The thesis concludes by comparing the two developed methods and discussing future research opportunities to enhance the performance of the aptasensor.

Canada is among the world’s leading producers and exporter of diluted bitumen (dilbit). Despite this, there is a lack of understanding surrounding the effects of dilbit spills in freshwater ecosystems. F2-isoprostanes (F2-IsoPs) are reliable biomarkers of oxidative stress, one of dilbit’s toxicity pathways in fish, however they are seldom studied in fish. This thesis describes the development of a non-invasive method for measuring F2-isoprostanes in the epidermal mucus of fish to measure oxidative stress in fathead minnows (Pimephales promelas) exposed to dilbit. An HPLC-MS/MS method was first developed and validated using Northern pike mucus (Esox lucius), and used to successfully detect F2-IsoPs in lake trout (Salvelinus namaycush) angled at the IISD-Experimental Lakes Area in Northwestern Ontario, proving these compounds are present at detectable concentrations in wild fish mucus. The relative concentrations of F2-IsoPs were then examined in tissues of rainbow trout (Onchorynchus mykiss) exposed to acute physical stress. F2-IsoP concentrations were also compared to total glutathione (GSH) and the GSH redox status in this study, finding a possible link between F2-IsoPs and GSH in gills and evidence of a mild oxidative stress response in physically stressed trout. The effect of dilbit on epidermal mucus and liver F2-IsoP concentrations was then examined in juvenile fathead minnows exposed for 7 days to 0-30% dilbit solutions, or water accommodated fraction (WAF). F2-IsoP concentrations did not differ significantly between any dilbit treatments: however this lack of response may have been caused by low uptake of polycyclic aromatic compounds. Liver and mucus F2-IsoPs were positively correlated in the control group and negatively correlated in the 30% WAF treatment. Finally, the developed method was field-tested in the Freshwater Oil Spill Remediation Study (FOReSt), a collaborative project aiming to determine the fate and behaviour of dilbit in a freshwater shorelin

Antimicrobial-resistant bacteria are emerging rapidly and causing antibiotics to become ineffective to treat infectious diseases which pose a threat to global public health. Multidrug-resistant bacteria are spreading rapidly and threaten to make it impossible to treat infections caused by these bacteria. Bacteria possess different types of mechanisms of antibiotic resistance. It is reported that modifications of membrane permeability, such as decreasing drug uptake (influx) and overexpression of efflux pumps that expel antibiotics from periplasm to the outside of the cell, are key contributors to the emergence of multidrug-resistant bacteria. Therefore, the development of rapid, sensitive detection techniques for antibiotic resistance is a significant focus in clinical diagnosis, disease control, environmental monitoring, and food safety. Electrochemical methods are advantageous as analytical tools due to their simplicity, high selectivity, sensitivity, rapid analysis and cost effectiveness. This thesis focuses on the development of robust electrochemical methods to quantify influx and efflux from bacteria. It covers the electrochemical characterization of common antibiotics and antibiotic hybrid molecules. This thesis demonstrates potential applications of drug influx and efflux quantification in bacterial cells using cyclic voltammetry and differential pulse voltammetry.