Name: Katrin Veldboer
Diploma / M.Sc degree: Westfälische Wilhelms-Universität Münster, Germany
(July 2007)

PhD Project: Cyclic phosphazenes for the surface modification of lanthanide phosphate-based nanoparticles


Homepage: http://www.uni-muenster.de/Chemie.ac/karst/group/veldboer.html

Abstract of Research Project

Lanthanide-based nanophosphors are a new class of nanoparticles and therefore there have only been a few reports according to their application as fluorescent labels. The lanthanide ions (Eu³⁺, Tb³⁺, Er³⁺, Tm³⁺) are characterised by unique optical properties such as long luminescent lifetimes, large stokes shift, narrow emission bands. A synthesis route for these nanoparticles has been developed by Haase and van Veggel et al. in 2000. The obtained particles are composed of an inorganic matrix and of organic groups on the surface, which protect the crystals against aggregation and control the growth of the particles. They are soluble only in nonpolar organic or aprotic polar solvents like dimethylformamide and dimethylsulfoxide, but not soluble in protic polar organic solvents or water. However, a good solubility of the nanoparticles in aqueous media is a major prerequisite for the intended bioanalytical applications as, for instance, fluorescence immunoassays. To achieve this aim, dedicated molecular surface modifiers are used to control the solubility and functionalisation of the nanocrystals.

Based on first experiments, which indicate that polycationic compounds are well suited to couple to the nanocrystal surface, a strategy for surface modification by cyclic phosphazenes has been developed. The versatile chemistry of the phosphazenes allows the easy introduction of quaternary ammonium functions and amino/carboxylate groups, while the solubility in water and methanol is improved by polar side chains. After the synthesis of different cyclic phosphazenes, their interaction with the nanoparticles has been investigated. For this purpose, fluorescence spectrometry as well as particle size measurements are used.
While aromatic functions may interfere with the UV absorbance of the nanocrystals, aliphatic side chains allow the fluorescence detection of the nanocrystals with UV excitation without loss of intensity compared with the native particles.


Katrin Veldboer
eMail: Katrin Veldboer