Abstract
Arsenic contamination in groundwater is a tenacious issue in various parts of the world. Owing to the toxicity of arsenic, its detection and analysis are important for national/global wellbeing of human and animals. This dissertation reports the development of two electrochemical aptamer biosensor on a nano-platform for selective detection of As(lll) in wastewater. In the process of fabricating the biosensor, different nanomaterials such as carbon nanoparticles (CNPs), gold nanoparticles (AuNPs) and iron oxide magnetic nanoparticles (MNPs) were used to facilitate electron transfer. A glassy carbon electrode was modified with CNPs by drop drying, then AuNPs were electrodeposited on the CNPs layer using cyclic voltammetry at 50 mV/s scan rate and a potential window of -400 mV to 1100 mV. The biosensor was prepared by immobilising a thiolated aptamer onto the nano-platform through the Au-S covalent linkage to form GCE/CNPs/AuNPs/Aptamer (aptasensor). The modified electrode (aptasensor) was characterised by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline, ferrocyanide and ruthenium electrolytes. The performance of the aptasensor was evaluated in different standard solutions of As(lll) and also in real water samples using square wave voltammetry. The aptasensor effectively detected As(lll) to a detection limit of 0.092 ppb. The results obtained were validated with ICP-OES and the analytical T-test showed that the two methods were in agreement. The aptasensor was selective in the detection of As(III) in the presence of other metal ions such as cadmium, copper and mercury.The second biosensor was fabricated by incubating a mixture of the aptamer and MNPs on screen printed carbon electrode (SPCE/MNPs-Aptamer). This aptasensor was characterized in a similar way to the GCE/CNPs/AuNPs/Aptamer. It was found to be selective and detected As(III) to a limit of 0.19 ppb (SWV) and 0.24 ppb (EIS). The detection limits were lower when compared to other previously reported As(III) biosensors. The biosensor showed good stability, hence they can be applied in monitoring As(III) in environmental water.
M.Sc. (Chemistry)