Detection of heavy metal ions using resistive pulse sensors

The main goal of this PhD was to expand the library of potential aptamers which can be used with Resistive Pulse Sensing (RPS) to enable a wider range of target analytes to be detected. Although RPS has been extensively applied with DNA aptamers for the detection of many different targets, including heavy metal ions, there are still many metal ions for which there are no known DNA aptamers. Here the focus was on the development of methods which utilise peptide aptamers and DNAzymes with RPS to expand this library. Further, the project looked to transfer the developed assays onto paper-based devices (PADs) to move towards a low-cost portable device. The first chapter presents a brief introduction to the nuclear decommissioning within the UK and how the NDA operates. It aims to provide some background to the overall aims of the project through outlining some of the current separation and analytical techniques which are employed for sample characterisation. The sensing methods used during this project were RPS and Ion Current Rectification (ICR) the literature review in chapter 2 focuses on the key aspects of these methods. The first project, outlined within in chapter 4, reports the first use of peptidecovered nanoparticles for the detection of nickel ions. It demonstrates how charge can be built into the peptides and showed a relationship between particle speed and concentration of nickel present. The specificity of the assay was established through incubation with a range of metal ions before finally the assay was then applied in real world samples through measuring nickel in dosed tap and pond water. Chapter 5 applies already designed DNAzymes to the detection of calcium ions. RPS was able to follow the structure changes of the DNAzyme, caused by the binding of calcium ions. The assay was shown to be catalytic in nature and allowed for tunability through incubation times. Again, the specificity of the assay was established through incubation with a range of metal ions before the assay was tested in real work samples. 3 Finally, presented in chapter six, is the use of PADs coated in different recognition elements for the detection of multiple metal ions simultaneously. The assay was able to indicate the presence of nickel, mercury and lead through changes in the current measured. The assays specificity and ability to work within environmental samples was also confirmed. The PADs were able to detect the three metal ions simultaneously. To summarise, the work presented within this thesis has expanded the library of potential aptamers that can be applied within RPS, hence expanding the library of potential targets for RPS. It has also developed a method which utilises ICR as the sensor and is able to measure multiple ions simultaneously. Through the work developed here, three published journal papers have been achieved and the work has been presented at several conferences.