Detection of pseudomonas aeruginosa quorum sensing molecules at an electrified liquid-liquid interface

The early detection of infectious diseases is vitally important to the improvement of their treatment. This has created the need for novel detection methods. Pseudomonas aeruginosa, a gram-negative multi-drug resistant pathogenic bacterium, is the cause of a high mortality rate amongst patients suffering from cystic fibrosis. The early detection of this bacteria is essential for effective treatment due to its ability to form a protective biofilm once established. The bacteria coordinate the formation of this biofilm through the release of quorum sensing (QS) molecules. Detection of these QS molecules would lead to a faster detection of P. aeruginosa than current methods. In this Master’s thesis, electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) is used as a new electroanalytic approach to detect two such QS molecules known to be actively used in QS by P. aeruginosa; 2-heptyl-3-hydroxy-4-quinolone (PQS) and its precursor 2-heptyl-4-quinolone (HHQ). This biphasic method does not depend on the redox activity of the QS molecules and avoids experimental complications due to the poor solubility of the hydrophobic QS molecules in aqueous media. Electrochemical monitoring was achieved through aqueous alkali metal ion and proton interfacial complexation with organic solubilised HHQ and PQS at a macro-sized (ca 1.53cm2 ) polarised water-1,2-dichloroethane interface. Using developed thermodynamic, analytical solutions to electrochemically induced liquid-liquid facilitated ion transfer, the proton:HHQ and proton:PQS binding stoichiometry’s were discovered to be 1:3 and 1:2, respectively, likely due to the relatively high concentrations of QS molecules employed. Miniaturisation of this analytical method to the microscale using borosilicate capillaries to house the aqueous phase yielded a proof-of-concept biosensor for QS small molecule detection which could be applied to a clinical setting with 1 μM detection levels. HHQ and PQS interfacial proton coordination was characterised at the micro-ITIES with proton:ligand stoichiometries of roughly 1:1, which correlated with the limit-of-linearity being reached as [proton]≈[ligand].