The assembly and modification of screen-printed platforms for electroanalytical applications

Foster, Christopher William (2015) The assembly and modification of screen-printed platforms for electroanalytical applications. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

This thesis reports upon the novel assembly and modification of screen-printed electrode systems. These key electrochemical proof-of-concepts have been benchmarked utilising voltammetric techniques, supporting the design of next-generation electrochemical sensing platforms, this thesis allows for proven laboratory-based approaches to be potentially up-scaled and commercially applied. Chapter 3 introduces the potential influence mechanical contortion upon the electrochemical performance of graphite based electroanalytical screen-printed platforms upon graphic paper, tracing paper and an ultraflexible polyester-based substrate are used. These sensors are electrochemically benchmarked against well-known redox probes hexxammineruthenium (III) chloride, potassium ferrocyanide and nicotinamide adenine dinucleotide (NADH). It was found that these ultraflexible based polyester-based electrodes are superior since they can withstand extensive mechanical contortion, yet still give rise to useful electrochemical performances. Most importantly the ultraflexible polyester electrodes do not suffer from capillary action as observed in the case of paper-based sensors causing the solution to wick-up the electrode towards the electrical connections. A new configuration is also explored using these electrode substrate supports where the working carbon electrode contains the electrocatalyst, cobalt (II) phthalocyanine (CoPC), and is benchmarked towards the electroanalytical sensing of the model analytes citric acid and hydrazine. Chapter 4 for the first time critically compares CoPC modified electrodes prepared by drop-casting CoPC nanoparticles (nano-CoPC) onto a range of carbon based electrode substrates with that of CoPC bulk modified screen-printed electrodes, towards the sensing of the model analytes L-ascorbic acid, oxygen and hydrazine. It is found that no “electrocatalysis” is observed towards L-ascorbic acid using either of these CoPC modified electrode configurations and that the bare underlying carbon electrode is the origin of the obtained voltammetric signal, which gives rise to useful electroanalytical signatures, providing new insights into literature reports where “electrocatalysis” has been reported with no clear control experiments undertaken. Chapter 5 presents a concise study upon the effect of in-situ bismuth, antimony, tin modified electrodes and combinations thereof towards the electrochemical detection of model analytes cadmium (II) and lead (II). It is found that the electrochemical response using the available range of metallic modifications is only ever observed when the underlying electrode substrate exhibits relatively slow electron transfer properties; in the case of fast electron transfer properties, no significant advantages are evident. It is demonstrated that a simple change of pH can allow the detection of the target analytes (cadmium (II) and lead (II)) at levels below that set by the World Health Organisation (WHO) using bare graphite screen-printed electrodes. Chapter 6 introduces the electroanalytical sensing of lead (II) ions utilising square-wave anodic stripping voltammetry where an increase in the electroanalytical sensitivity is observed by a factor of 5 with the screen-printed back-to-back microband configuration. Upon application of this configuration towards the quantification of lead (II) ions, within drinking water corresponds to a concentration of 2.8 (±0.3) μg/L. Independent validation was performed using ICP-OES with the levels of lead (II) ions found to correspond to 2.5 (±0.1) μg/L; the excellent agreement between the two methods validates the electroanalytical procedure for the quantification of lead (II) ions in drinking water. Finally, Chapter 7 examines for the first time, characterisation of the number of drawn pencil layers and the grade of pencil; these parameters are commonly overlooked when utilising PDEs. It is demonstrated that a PDE drawn ten times with a 6B pencil presented the most advantageous electrochemical platform, in terms of electrochemical reversibility and peak height/analytical signal. These PDEs have demonstrated beneficial electroanalytical capabilities towards p-benzoquinone and the simultaneous detection of heavy metals, namely, lead (II) and cadmium (II) all of which are explored for the first time utilising PDEs. Initially, the detection limits of this system were lower than desired for an electroanalytical platforms, however implementation of PDEs in a back-to-back configuration (as shown within Chapter 6), the detection limits for lead (II) and cadmium (II) correspond to 10 μgL-1 and 98 μgL-1 respectively within model aqueous (0.1 M HCl) solutions.