Investigation of novel screen-printed electrochemical sensors for measuring 17-βeta-Estradiol in an aqueous environment

Musa, Auwal

Abstract

The hormone 17β-estradiol (E2) is increasingly prevalent in environmental waters globally, posing a significant threat to human and animal health due to its adverse effects on endocrine functions. Traditional methods of analysing E2 are complex and time-consuming, lacking the ability to provide real-time analysis. Electrochemical sensors that utilise screen-printed electrodes present a cost-effective, uncomplicated, and portable alternative for conducting on-site analyses. There is a research gap regarding using nanomaterials as modifiers for screen-printed electrodes in developing electrochemical sensors to monitor environmental estradiol. This thesis examines modifying screen-printed electrode surfaces with carbon-based materials to provide cost-effective materials for electroanalysis of the E2 hormone. This study emphasises the employment of carbon materials in the electrochemical analysis of E2. Various techniques are utilised to study the sensors' electrochemical properties and structural characteristics, including cyclic voltammetry (CV), amperometry, and differential pulse voltammetry (DPV). In addition, methods such as scanning electron microscopy (SEM), ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier-transform infrared (FTIR), and Raman spectroscopy are employed to elucidate the physical and chemical structures of materials.
Chapter 2 presents foundational information on this thesis's fundamental electrochemistry and conventional electrochemical methods. Additionally, this chapter provides an extensive survey of prior research concerning using screen-printed electrodes for E2 analysis. Chapter 3 results illustrate that a carbon spherical shell material modified screen-printed electrode (CSSM/SPE) has two linear plots within concentration ranges of 0.83 – 2.49 μM and 3.31 – 4.98 μM. The limit of detection
(LOD) was calculated as (n = 3), the standard deviation of the signal response against the slope of the calibration plot. For lower and higher concentration ranges, the sensitivities were 0.273 μA μM-1 cm-2 for CSSM/SPE and 0.118 μA μM-1 cm-2 for bare SPE, respectively.
Chapter 4 explores the use of graphene-based electrodes in the electrochemical determination of E2 using an amperometric method and illustrates that the direct electrooxidation of E2 offers advantages. These include cost-effectiveness, eliminating the need for expensive enzymes, and stability against temperature and pH changes. Graphene has remarkable properties such as high electron transfer, high conductivity, robust mechanical characteristics, and a large surface-to-volume ratio. Although many electrochemical sensors suffer from electrode fouling due to the electrochemical oxidation of E2's phenolic group, which forms an insoluble layer on the working electrode and affects performance, graphene-based electrodes can overcome this challenge. In this study, graphene screen-printed electrodes (GHSPE), electrochemically exfoliated graphene-modified electrodes (EEFGHSPE), and 3D graphene foam screen-printed electrodes (3D-GFSPE) were compared. The analytical performance of these sensors was observed at an applied potential of +0.65 V (vs. Ag/AgCl) across the concentration range of 0.83 to 4.98 μM estradiol. Sensitivities of 0.495 μA μM−1 cm−2, 0.121 μA μM−1 cm−2, and 0.264 μA μM−1 cm−2 were determined for GHSPE, 3D-GFSPE, and EEFGHSPE, respectively, with detection limits of 0.71 μM, 0.41 μM, and 0.33 μM (n=3). Subsequently, the possibility of determining E2 levels in a potable tap water sample by amperometry was investigated over the concentration range of 0.83 – 4.98 μM.
In Chapter 5, a screen-printed electrode (SPE) modified with gold nanoparticles decorated within reduced graphene oxide carbon nanotubes (rGO-AuNP/CNT/SPE)
was studied for E2 determination. The AuNPs were produced through an eco-friendly method utilising a plant extract, eliminating the need for less environmentally friendly chemicals and reagents and removing the requirements of sophisticated fabrication methods and tedious procedures. Additionally, rGO-AuNP serves as a dispersant for the CNT to improve the dispersion stability of CNTs. The composite rGO-AuNP/CNT/SPE exhibited a notable improvement compared to bare/SPE and GO-CNT/SPE, as evidenced by the relative peak currents. The optimised E2 sensor offers linear sensitivity from 0.05 - 1.00 μM with a LOD of 3.4 nM based on three times the standard deviation (3σ). Notably, this sensing approach yields stable, repeatable, and reproducible outcomes. Assessment of drinking water samples indicates an average percentage recovery of 97.5% for samples fortified with E2 at concentrations as low as 0.5 μM, with a coefficient of variation (% CV) value of 2.7%. Chapter 6 investigated the use of a disposable electrochemical sensor that utilised a deep eutectic solvent (DES), molecularly imprinted polymer (MIP), and carbon paste printed electrode (CPE). The DES served as a solvent binder for MIP and for the homogenisation of the carbon paste. The MIP was made conductive with carbon paste for electrochemical transduction. This method addresses the slow diffusion and rebinding kinetics of analytes and the cavities of the MIP for use in electrochemical sensors. Experimental parameters were optimised, and the sensor exhibited a linear range of 0.83 μM to 4.98 μM. This approach demonstrates the possibility of using CPE and MIPs as disposable sensors that afford simplicity, ease of production, and low cost.

Citation

Musa, A. Investigation of novel screen-printed electrochemical sensors for measuring 17-βeta-Estradiol in an aqueous environment. (Thesis). University of the West of England. Retrieved from https://uwe-repository.worktribe.com/output/9006674

• Thesis Type: Thesis
• Deposit Date: Feb 11, 2022
• Publicly Available Date: May 21, 2024
• Public URL: https://uwe-repository.worktribe.com/output/9006674
• Award Date: May 21, 2024