Sensory Lipid Membrane Films with Integrated Inorganic Coordination Complexes

Anion detection and recognition in pure water is a significant current challenge in supramolecular chemistry, to this day remains relatively unevolved as a research field. This is due to the fundamental challenges associated with sensing anions, attributed to their strong association with surrounding water molecules (high solvation energies) that needs to be broken in order to bind to a receptor.

These receptors often have low solubility in water and poor selectivity for the target anion, exacerbated by weak anion affinity to the binding site.

Inorganic phosphate is ubiquitous as a chemical building block in biological systems, for example being present in the majority of metabolic reactions. It is also highly environmentally relevant, whereby the rising use of fertilisers in agriculture has led to an overabundance of phosphates in waterways. This results in eutrophication, the effects of which can be seen in harmful algal blooms and hypoxic 'dead zones' of aquatic life.

Common techniques of detecting phosphate levels vary from the use of traditional molecular fluorescence probes and optical analysis to NMR titration techniques. However, these lab-based methods are typically expensive, time consuming and laborious. Electrochemical sensors, in contrast, are portable, cheap and can be used in the field for continuous monitoring.

The binding environment of a receptor for anions can be effectively engineered to promote high affinity, or strong binding, between the receptor and targeting anion. Sensory films exhibit measurable binding enhancement factors, where solvation effects are controlled. A practical way of controlling such effects is by using such films which afford the ability to tune the interfacial dielectric microenvironment, such that there is reduced charge screening, and hence stronger interactions between the charged anion and binding site.

In this project we will develop artificial hydrophobic lipid bilayers, which are an example of such organic sensory films, whereby anion binding motifs can be readily integrated into these bilayers. These membranes will be immobilised on an electrode surface in order to obtain an electrochemical sensor. Electrochemical capacitance measurements will be taken at the interface between the electrode and the film by applying a fixed voltage and varying frequency using a low magnitude alternating current.

These capacitance measurements will effectively probe the ability of the film is able to store charge, i.e. the frequency and strength of binding events of phosphate to the membrane anchored receptors at the electrode surface, and as such, quantify phosphate levels.

This project falls in the EPSRC electrochemical sciences, sensors and instrumentation, synthetic coordination chemistry, synthetic supramolecular chemistry research areas within the physical sciences research theme.