Polymeric hydrogels for fluorescent sensing applications

Abstract

Polymeric hydrogels are cross-linked three dimensional networks that can absorb and retainlarge amounts of water. They also demonstrate excellent biocompatibility, are relatively cheap and can be prepared using straightforward procedures. Photoinduced electron transfer (PET) is a mechanism which can prevent emission from a fluorescence sensor when a target analyte is absent from the sensor binding site. However, when the target analyte binds, the PET mechanism is cancelled and fluorescence is observed. Combining fluorescence sensors with polymeric hydrogels offers the potential for developing materials that respond to changes in their local environment by a modulation of their fluorescence signature. In this thesis polymeric fluorescent sensors based on the PET mechanism will incorporated within polymeric hydrogels and their response to target analytes evaluated.The first results chapter (chapter 2) discusses the synthesis, characterisation and photophysical evaluation of a Zn(II) selective PET sensor. The sensor was then grafted onto a poly(allylamine) backbone along with a calibration fluorophore giving a ratiometric, polymeric Zn(II) responsive sensor. The polymer was successfully incorporated into a Gantrez-based hydrogel formulation and shown to be capable of determining Zn(II) levelsratiometrically.The second results chapter (chapter 3) discusses the use of a pair of commercially available dextran conjugated probes; fura-dextran and texas-red® dextran for their ratiometric response to Ca(II) levels subject to varied conditions of dilution and Ca(II) levels. These were shown to be capable of determining Ca(II) levels from 0 - 12 mM under a range conditions ratiometrically. Attempts to incorporate this pair of probes into hydrogel formulations were undertaken, however these were unsuccessful. Further testing in alternative hydrogels should enable extension of this approach to within hydrogel-based systems.In the third results chapter (chapter 4), a similar type Zn(II) responsive sensor as in results chapter 1 with methacrylate functionality was synthesised, characterised and it’s photophysical properties evaluated. After redox initiated polymerisation at roomtemperature, the polymeric hydrogel sensor was fixed onto the bottom of 96-well plates and proved capable of determining Zn(II) levels in aqueous buffer in the 0.25 – 1.75 mMrangeFinally, results chapter 4 (chapter 5) discusses the co-polymerization of the methacrylate-functionalized Zn(II) sensor synthesised in results chapter 3 (chapter 4) with HEMA, PEG methacrylate and methacroxyethyl thiocarbamoyl rhodamine B monomers to yield a Zn(II) responsive, ratiometric, cell-permeable and non-toxic polymeric sensor. The photophysical properties and cell toxicity of this probe were characterised, and the intensity offluorescence shown to be dependent on the intracellular concentration of Zn(II).

Date of Award	Jan 2015
Original language	English
Supervisor	John Callan (Supervisor), Bridgeen Callan (Supervisor), Paul McCarron (Supervisor), Bridgeen Callan (Supervisor), John Callan (Supervisor) & Paul McCarron (Supervisor)