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Title: An electrochemical sensor for efavirenz based on electrode modification with silver-gold bimetallic nanoparticles functionalised nanoclay
Authors: Ngcobo, Sizwe 
Keywords: Antiretroviral agents -- Analysis;Pharmaceutical chemistry;Nanotechnology;Electrochemical sensors
Issue Date: 2022
Publisher: Cape Peninsula University of Technology
Abstract: This study synthesized Ag and Au NPs through chemical reduction method, whilst Ag-Au was synthesized through co-reduction method where sodium citrate was used a reducing agent for both monometallic and bimetallic synthesis. Corresponding metallic nanoclay composites, Ag-PGV, Au-PGV and Ag-Au-PGV bentonite were all synthesised through similar synthesis methodology as metallic NPs as metallic NPs were reduced unto PGV nanoclay bentonite. The metallic NPs and their nanoclay composites were optically characterized through Fourier-transformation infrared spectroscopy (FT-IR), UV/Visible spectroscopy (UV/Vis), Scanning electron microscopy (SEM) and X-ray diffraction (XRD). However, characterization using UV/Visible spectroscopy was conducted for metallic NPs and not composites due to colloidal nature of composites. Ag and Au monometallic exhibited 436 nm and 512 nm specific characteristic wavelengths whilst Ag-Au bimetallic NPs exhibited characteristic wavelengths of 414 nm and 516 nm for Ag and Au, respectively. FT-IR mainly depicted COO- functional groups which confirmed successful capping of metallic NPs and nanoclay composites. XRD exhibited diffraction planes which are related to 2θ values both Ag and Au metals, and both were largely depicted in diffraction planes of Ag-Au bimetallic NPs. As confirmation of successful functionalization of PGV bentonite clay, similar diffraction planes were observed in Au-PGV, Ag-PGV and Ag-Au-PGV bentonite composites, respectively. SEM depicted nanoclay composites average particle size as significantly bigger than that of metallic NPs, the shape of particles of metallic NPs were resembled in their clay composites, which confirmed functionalization of bentonite clay. The evaluation of electrochemical properties of metallic NPs and clay composited were obtained through use of Cyclic voltammetry (CV). Transducers were fabricated through drop-coating of metallic NPs and clay composites sensing films method .CV showed that bentonite nanoclay is largely insulated by silicates but exhibited small electroactivity of Fe. The electroactivity of Ag and Au monometallic, Ag-Au bimetallic NPs appeared similar, whilst clay composites depicted similar peak potentials as those observed for monometallic and bimetallic NPs. A study of electrochemical properties of metallic NPs and their clay composites carried using 0,1 HCl as supporting electrolyte obtained through electrochemical parameters from both Randles-sevcik and Laviron’s methods depicted parameters such as surface coverages(Γ), electron-transfer rate constants (Ks), electron-coefficient(nα) and diffusion coefficients(D). Ag-Au-PGV was deduced as superior sensing film as it exhibited, 2,16Γ, 1,76 Ks, 0,07nα 2,29 x 10-8 cm2/s parameters, which were superior to other sensing films. Consequently, Ag-Au-PGV composite as best modifier was used as platform with addition of human serum albumin (HSA) in detection of EFV using DPV, which was the best detection technique. Experimental and detection parameters optimization were deduced and drop-casting method was deduced as best modifier method whilst 1M PBS as supporting electrolyte. Optimized detection parameters which included, step-potential, pulse amplitude, and initial potential were determined to be 0,015V/s, 0,085Vs-1 and 1,15V. Varying of step-potential was used to determine the kinetic parameters of electrooxidation of EFV. Through Randles-Sevcik and Laviron equations, kinetic parameters were determined to be 1,11 Ks, 0,2 α and 2,76 x 10-9 cm2/s in electrocatalytic reaction with Ag-Au-PGV/HSA platform. The electrocatalytic reaction mechanism produced a single electron-transfer between platform interface and EFV. The calibration curve exhibited EFV Limit of detection (LOD), Limit of quantitation (LOQ) and Sensitivity of 0,13 uM, 0,4uM and 2,53 x 10-9 uA uM-1 cm-2. Inteferences studies of EFV demonstrated plausible selectivity of platform, as 83% and 94% EFV content were recovered in sample matrix containing glucose, ascorbic acid and sodium chloride, whilst reproducibilty and repeatability of detection of EFV starndard were statisticallly plausible with RSD values of 4,90% and 3,21%, respectively. Real sample applicability of a platform evaluated from EFV spiking urine samples produced EFV recoveries of 94% and 115% , respectively. EFV mass concentration experimentally obtained from commercial capsules avaraged to 192.02 mg. This were comparable to 200 mg EFV concentration specified by commercial manufacturer of EFV capsules, whilst stability of the Ag-Au-PGV/HAS platform demonstrated performance deteriotation rate of 10% after 3 days for spiked EFV samples whilst 20% for EFV pharmacuetical capsule.
Description: Thesis (Master of Applied Science in Chemistry)--Cape Peninsula University of technology, 2022
Appears in Collections:Chemistry - Masters Degrees

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