Development of new fluorescence spectroscopy approaches for the study of silica

PDMPO (2-(4-pyridyl)-5-((4-(2dimethylaminoethylaminocarbamoyl)methoxy)phenyl) oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-visible and fluorescence spectroscopy supported by computational data, dynamic light scattering and zeta potential measurements to understand the PDMPO-silica interaction. From absorption data, PDMPO exhibited a pKa of 4.20 for (PDMPOH22+ to PDMPOH+). Fluorescence emission measurements revealed large shifts in excited state pKa* values with different behaviour when bound to silica ( pKa* of 10.4). There is size dependent shift in pKa*. pKa* value of 9.60, 10.20, 10.50, 11.40, 11.44 was retrieved for 22 nm, 30 nm,50 nm, 77 nm and 133 nm particles respectively. PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH+* and dielectric constant (4.8-80). Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3-5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification. A linear relationship was observed between PDMPO emission ratio and zeta potential measurements were used to determine charge on the silica nanostructures exhibited by Equisetum arvense and Nitzschia stellate. This thesis also report an optical sectioned planar format assay (OSPFA) using confocal microscopy to study silica biomolecule interaction (amino acids and silica binding peptides ( pep 1) ) using a PDMPO displacement assay.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Nottingham Trent University

Year dc:date.issued

2016

Author dc:creator

• Parambath, M

Language dc:language

en