Wireless And Conventional Electrochemiluminescence For Analytical Applications

Download or read book Wireless and Conventional Electrochemiluminescence for Analytical Applications written by Samantha Douman and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrochemiluminescence (ECL) or alternatively electrogenerated chemiluminescence is a light-emitting process brought about by electron-transfer reactions. ECL can occur via two pathways namely, ion annihilation and coreactant pathway. Coreactant ECL generation predominates over annihilation pathway due to the ease of ECL generation in aqueous solution. The discovery of ECL emission in aqueous media has led to major applications in analytical chemistry, especially in the field of biosensing, that is, immunoassays and DNA-probe assays. Thus, the scope of this work was to develop a simple, sensitive ECL immunosensor for cardiac injury and to study and present newly fabricated platforms for analytical applications by using conventional and bipolar ECL as detection mechanism. Herein, two types of electrodes were investigated, that is, thin film electrodes made up of carbon micro-particles and three-dimensional (3D) printed electrodes made up of titanium alloy (Ti-6AI-4V) powder. The generation of ECL at these electrodes was based on two approaches, that is, ECL generated by conventional electrochemistry and ECL generation based on bipolar or wireless electrochemistry. Firstly, the conductivity of the thin film electrodes as well as their ability to generate ECL was investigated. The obtained results revealed that the films exhibited very low conductivity (6 × 103 S m−1) for low carbon particle loadings, but once the percolation threshold was reached (volume percentage of 71 ± 8% carbon particles), the conductivity increased dramatically and a maximum conductivity of 2.0 ± 0.1 × 107 S m−1 was achieved. The electrochemical properties of the thin film electrodes, including heterogeneous electron transfer rates, were probed using cyclic voltammetry. While the structural and topographical analysis was achieved by Raman and scanning electron microscopy, respectively. Significantly, bipolar ECL can be generated with films that contain 65% (by volume) carbon particles using [Ru(bpy)3]2+ as the luminophore and tripropylamine as the coreactant, at an electric field of 14 V cm−1. A simple additive 3D printing technique based on selective laser melting (SLM) technology was used to fabricate 1 cm2 footprint 3D-printed titanium electrodes. The 3D-printed structures were characterised topographically and electrochemically by scanning electron microscopy and cyclic voltammetry, respectively. An electrochemical surface modification method was used to functionalise the surface of the 3D titanium electrodes with a thin gold layer which significantly enhanced the dynamics of heterogeneous electron transfer. Despite the slow rate of heterogeneous electron transfer at the bare 3D titanium electrodes, significant ECL was generated and the intensity increased with increasing scan rate. The obtained results suggest that it's possible to fabricate customisable electrodes with control over the morphology, size, and performance, thus opens up exciting new possibilities for specific functions and studies like chemical sensing and biology, respectively. Secondly, the thesis focused on the synthesis, characterisation and application of an interesting ECL luminophore, ruthenium (II) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5-f][1,10]phenanthroline [Ru(bpy)2(picCOOH)]2+. The luminophore was found to exhibit impressive electrochemical and photophysical properties, and for this reason, was covalently coupled to a secondary antibody via NHS/EDC for employment as ECL emitters in the fabrication of a sandwich-type immunosensor for the detection of cardiac troponin I, an important biomarker for cardiac injury. The ECL immunosensor was fabricated by the assembly of a new custom-made primary antibody with a carboxylic acid-terminated alkanethiol modified gold electrode. The primary antibody modified gold electrode was first treated with 1% bovine serum albumin and thereafter it was reacted with various concentrations of human cardiac troponin-I, followed by the introduction of the secondary antibody dye-conjugate. In the presence of the tripropylamine coreactant, an increase in ECL signal was observed. The ECL intensity versus the concentration of cardiac troponin I was linear in the range from 0.001 pg mL-1 to 0.50 pg mL-1 with an extremely low detection limit of 0.03 pg mL-1 (SD, n=3). Furthermore, this immunoassay was extended to a bipolar electrochemical system so that wireless detection of cTnI could be realised. Comparison studies were also carried out to study the difference in ECL intensity between conventional and bipolar ECL approach.