Electrochemical anion sensing at self-assembled monolayers and polymeric interfaces

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Anionic species are relevant targets in a multitude of fields for biological, medicinal and environmental applications. Thus, there is significant demand for the development of approaches for selective, sensitive and practically applicable anion sensing, particularly in competitive media (which is required for most real-world applications). Electrochemical methods (voltammetric, impedimetric or potentiometric) provide a powerful yet relatively experimentally simple approach to probe synthetic receptors in solution or at interfaces, which would be otherwise challenging to probe with other routinely used techniques like NMR or UV-Vis spectroscopy. Immobilisation of a sensor onto a surface (often in self-assembled monolayers, SAMs) offers a number of advantages, including bypassing receptor solubility limits, significantly reducing the quantity of receptor required and can also provide a sensing amplification due to preorganisation and dielectric effects at an interface. The anion sensing capabilities of a number of anion receptive, redox-active receptors have been investigated thus far (often containing hydrogen bonding (HB) binding sites) but an area which is largely underdeveloped is interfacial, electrochemical sensing of anions with halogen bonding (XB) based receptive motifs. Halogen bonding has been shown to be a strong, directional non-covalent interaction that often outperforms HB analogues and therefore presents an opportunity to improve anion sensor designs. Further to this, an exploration of receptive, polymeric interfaces with XB motifs offers an investigation into possible multivalent, dielectric and electric field effects that could greatly influence the efficacy of anion binding/sensing at an interface. This project aims to investigate the anion binding capabilities of self-assembled monolayers with HB/XB-based binding motifs (e.g. proto- or iodotriazoles) via various electrochemical techniques (particularly voltammetric and impedimetric sensing), and then progress to studying interfacial electrochemical anion sensing under flow, which is unprecedented for a sigma bonding interface. A systematic study with a range of anions will be conducted in competitive solvent media (ACN/H2O systems) and comparisons will be drawn between HB and XB analogues. Furthermore, a comparison between discrete receptors in SAMs and polymeric films with a similar redox-active, XB-based design will be investigated. A methodology will be developed for surface-initiated polymerisation of this receptive monomer motifs (both redox-tagged and not) using a controlled radical polymerisation procedure such as atom transfer radical polymerisation (ATRP) or reversible addition-fragmentation chain-transfer polymerisation (RAFT). This will be followed by extensive characterisation of the resulting films (e.g. polydispersity, film thickness, voltammetric behaviour) and comprehensive electrochemical sensing studies for a range of anionic species.This project falls within the EPSRC Physical Sciences research area: analytical science, electrochemical sciences, polymer materials.