Fluorescence imaging characterisation of silicates

The Aim: This multidisciplinary project is to investigate the use of fluorescence recovery after photobleaching (FRAP) microscopy and related techniques to characterise the diffusion of nm structures in silicate liquors, which influences the efficacy of these liquors in many applications including the manufacture of porous silicas. The silicate manufacturing conditions that control the size and number of colloidal species in these liquors is poorly understood, largely because of a lack of techniques to properly characterise the resulting silicates.
Background: Although FRAP is more usually used for the study of biological systems, a feasibility assessment by PQ Corporation some years ago suggested FRAP offers a promising approach to better understanding silicate liquors. A successful outcome of the project would deliver a figure of merit with which to compare silicates that would significantly improve understanding of the relationships between silicate manufacture, structure and performance. The project builds on a long-standing collaboration between PQ and Strathclyde' Photophysics Group which led, amongst other outcomes, to a new method of silicate nanoparticle metrology [1,2].
The operating principle of FRAP requires photobleaching of a microscopic area and recording the transient fluorescence intensity recovery as a consequence of the diffusion of fluorescent species re-entering the area under study.
At present there is no FRAP capability in-house at the collaborating company but, through this project, a FRAP system will be assembled, developed and tested at Strathclyde using samples that PQ will provide. The Photophysics Group has the optical design, fluorescence and data analysis expertise required to construct and characterise the instrument. The Group also possesses an expansive range of complementary instrumentation to compare results and optimise the FRAP performance. The instrument can be replicated for on-site use at PQ once developed and proven. The student will gain valuable industrial experience working at PQ in the UK as part of the project, experience that will be essential in optimising instrument performance.

The aim of the project will be achieved by completing several key objectives (project deliverables):
1. The assembly of a FRAP microscopy system to include laser excitation, microscope assembly, optical couplings, synchronisation electronics, photon detection and associated image analysis software.
2. Assessment of the optimum fluorescence dyes for FRAP over a range of acidic and alkaline pH.
3. Testing and calibration of the FRAP system on well-characterised and standard silicate sols including comparison with other methods such as light scattering, fluorescence anisotropy and fluorescence correlation spectroscopy.
4. Modelling the silicate particles diffusion and the observables detected by FRAP and other complementary techniques used (molecular dynamics, excited-state kinetics, experiment design). Determining the best-fit models and optimisation of the experimental procedure.
5. Silicate characterisation and correlating data from the improved FRAP technique with process variables (e.g. presence of Fe, Al, Ca, Mg) that may influence the type, number and size of colloidal species present in the silicate. PQ will provide silicate samples where manufacturing conditions have been altered in a systematic way.
6. Studies on samples stability and ageing (all the silicates will be metastable).
7. Using the FRAP technique to further improve understanding of the manufacture of silicates, their structure and how both of these influence product efficacy.