Circularly Polarised Luminescence Spectroscopy of Functionalised Lanthanide Complex for Sensing and Imaging

Abstract

This work is based on circularly polarised luminescence spectroscopy of functionalised Lanthanide (III) ion complexes that can be used for sensing and imaging. Work was also done to design optical acquisition systems for the accessories to a confocal microscope that would be modified to facilitate measurements of circularly polarised luminescence for bio-imaging. This work describes some aspects of the interactions between chiral biological molecules and functionalised optical emissive probes. The interaction between a target analyte (the biological molecule) and the probe results in a modulation of the polarisation of the emission, which is readily, studied using circularly polarised luminescence spectroscopy. Circularly polarised luminescence spectroscopy is based on the differential emission of left and right circularly polarized radiation by luminescent chiral systems. The primary observables in circularly polarised luminescence spectroscopy are the emission circular intensity differential. The systems used in this study are the luminescent Lanthanide (III) ion complexes, which have proven to be a productive area of research due to their unique optical properties enabling their use in a wide range of applications. A major drawback to using Lanthanide (III) ion is their low extinction coefficients; hence the antenna effect is often used to overcome this problem. In this way, the antenna chromophore absorbs incoming radiation and transfers the energy to the Lanthanide leading to indirect excitation of the Lanthanide (III) ion. These and similar complexes have shown an ability to bind to biologically important anions such as carbonate and phosphate in aqueous media and are able to report this event by a modulation in the Photo luminescence. These interactions have also been investigated by monitoring the emitted circularly polarised light using the technique described. Typical circularly polarised luminescence spectra of the europium (III) ion complexes will be presented as will the binding study results and a detailed account of how the spectra is obtained.