Development of Electrochemical and Optical Sensing Methodologies for Food Toxicants

Food is a source of energy and an essential part of our lives. Food processing has evolved and developed over time due to increasing populations and the availability of non-seasonal food for everyone at all times. However, food processing methods (such as thermal, fermentation, irradiation, etc.) lead to the formation of toxicants in food matrices. This thesis focuses on acrylamide (AM) and acetaldehyde (AcH) due to their high toxicity (carcinogenicity), high abundance in processed food. Therefore, developing sensing methodologies to ensure food safety for consumers is critical.Chapter 3 presents the electrochemical sensing of AM using poly(methylene blue) (PMB) on a glassy carbon electrode (GCE), where PMB functions as an electrochemical reporter. PMB was modified onto the GC by the electrochemical polymerisation method. Electrochemical sensing of AM was facilitated by the interaction between AM and PMB. The association constant of AM with PMB/GCE was found to be 8.9 × 10^6 M⁻¹. This result indicated a strong interaction of AM on the PMB/GCE surface.Chapter 4 presents the electrochemical sensing of AM using 4-mercaptobenzoic acid (4-MBA)-modified over a gold electrode (GE). 4-MBA was adsorbed onto the gold electrode using the cyclic voltammetry technique. Electrochemical sensing of AM was facilitated by the formation of an adduct between AM and 4-MBA through hydrogen bonding. The electrochemical performance was assessed using cyclic voltammetry and square wave voltammetry. Cyclic voltammetry analysis shows a decrease in reduction current of the gold electrode upon the addition of AM. The association constant and binding number of AM with 4-MBA/GE were calculated using square-wave voltammetry and found to be 0.5 × 10^6 M⁻¹ and 1.2 (~1), respectively. The calculated association constant is almost comparable to that of DNA interaction with AM, which reveals that 4-MBA acts as a better recognition element than DNA.Chapter 5 presents a fluorescence sensor using commercially available rhodamine B (RhB) as a fluorescent reporter for AM detection. The method utilises the fluorescence quenching (λex = 256 nm) and enhancement (λex = 304 nm, 354 nm, and 402 nm) properties of RhB in the presence of AM. Mechanistic studies on fluorescence quenching and enhancement have been conducted using ultraviolet-visible, nuclear magnetic resonance and fluorescence spectroscopy. Additionally, temperature-dependent fluorescence studies confirm the dynamic quenching process. These results reveal that PMB, RhB and 4-MBA can replace haemoglobin as a molecular recognition element.Chapter 6 shows the enhanced peroxidase activity of Co(OH)₂ while it binds with an AM-specific aptamer, which retains its catalytic activity while AM binds with the AM-specific aptamer. Moreover, this method shows a detection range from 0.02 nM to 200 nM. This characteristic phenomenon is used to develop a colourimetric sensing methodology for AM in picomolar level detection.Chapter 7 shows electrochemical sensing of AcH. Here, electrochemically activated copper nitroprusside (CuNPr) produces Cu¹⁺ over the GCE. This Cu¹⁺ ion can oxidise AcH into acetic acid. This chemical reaction-assisted electrochemical process is used to develop an electrochemical sensor for AcH.