Healy, Bronach Michelle (2022) The Electrochemical Detection of Acetaminophen and the Enantioselective Recognition of Tyrosine Enantiomers using a modified carbon-based electrode. Masters thesis, National University of Ireland Maynooth.

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Abstract

The beginning of this thesis sees the development and characterisation of a β-cyclodextrin (β- CD) based electrochemical sensor for the electrochemical detection of acetaminophen (paracetamol) and the influence of the accompanying activation of the glassy carbon-based substrate. To incorporate the β-cyclodextrin onto the glassy carbon electrode, electropolymerisation from an aqueous solution of the β-CD monomer was carried out, attempting to form a polymeric β-CD film. The modified electrode was characterised using cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy (SEM) coupled with electron dispersive X-Ray analysis (EDX). Optimum conditions for the formation of the sensor were obtained by selecting an ideal potential window, applied potential and also selecting the suitable number of cycles required for modification. A highly efficient sensor was formed when cycling occurred between -2.0 to 2.2 V (vs. SCE) cycled for 15 cycles. The role of the activation of the GCE was also investigated and found to greatly enhance the electrochemical performance of the sensor. It was found that cycling the GCE in a 1.0 M phosphate buffer solution (PBS) at pH 5.5, from -2.0 to 1.1 V (vs. SCE) for 5 cycles, produced a nearly identical voltammogram when compared to a voltammogram where both activation and the electropolymerizing processes on the GCE surface occurred. The modified sensor achieved good sensitivity towards acetaminophen at a neutral pH with a peak current density of 3.8 mA cm-2, with the oxidation of acetaminophen being influenced by pH in which peak currents became lower in more alkaline solutions. In addition, a wide variety of interfering compounds was examined to establish their effect, if any, on the detection of acetaminophen using the β-CD modified GCE. The study concluded that the oxidation of acetaminophen was not influenced by the addition of any of the interference compounds and the sensor was capable of achieving high selectivity. The final part of this thesis explores the development and characterisation of a chitosan and graphene-modified GCE (CS/GO- GCE) for the electrochemical enantioselective recognition of tyrosine enantiomers. Graphene was incorporated into the sensor by electrodeposition from an aqueous graphene nanoplatelet (GO) dispersed in a 5 mM β-CD solution to prevent agglomeration of the graphene sheets. The biopolymer chitosan was incorporated by electrodeposition from 1% chitosan hydrogel solution (CS) dissolved in 0.2 M acetic acid. The presence of GO and CS were confirmed using cyclic voltammetry, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and potentiostatic measurements. Optimum conditions for development of the CS/GO-modified GCE involved investigating solvent and polymer concentration of the chitosan hydrogel solution, analysis of the supporting electrolyte used and examining the time sensitive diffusion of molecules into the hydrogel. Electrodeposition of graphene was accomplished by cycling from -1.5 to 0.8 V (vs. SCE) for 5 cycles at 50 mV s-1 using cyclic voltammetry, whilst deposition of the adherent hydrogel polymer was achieved by potentiostatic measurements held for 5 min at -1.5 V (vs. SCE). FTIR spectra showed a combination of CS and GO characteristic peaks suggesting the GO become encapsulated in the CS polymer on the surface of the GCE. The CS/GO-modified GCE achieved good enantioselective recognition between the tyrosine (Tyr) enantiomers, with preferential binding towards L-Tyr displayed. The presence of the chiral hydrogel polymer enabled enantioseparation capability of sensor however it reduced the electrochemical sensitivity of the sensor.

Item Type:	Thesis (Masters)
Keywords:	The Electrochemical Detection of Acetaminophen and the Enantioselective Recognition; Tyrosine Enantiomers; modified carbon-based electrode;
Academic Unit:	Faculty of Science and Engineering > Chemistry
Item ID:	17361
Depositing User:	IR eTheses
Date Deposited:	23 Jun 2023 10:55
URI:
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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