Energy transfer probe as a tool to study morphological and structural origins of fluorescence quenching in rare-earth doped nanophosphors

Abstract

Uute vähidiagnostika meetodite arendamine on moodsa meditsiini üks põhilisi uurimisvaldkondi. Sügaval paiknevate vähirakkude fluorestsentskuva võib osutuda toimivaks mitteinvasiivseks diagnostikameetodiks. Fluorestsentskuva realiseerimiseks on välja pakutud mitmeid potentsiaalselt sobivaid materjale. Suurt huvi pakuvad haruldaste muldmetallidega dopeeritud nanoosakesed, mis on orgaaniliste luminofooride ja kvantpunktidega võrreldes parema bioloogilise sobivusega ning samas ka foto- ja termostabiilsemad. Paraku nende fluorestsentsomadused vajavad viimistlemist. Põhiprobleemiks on fluorestsentsi kustutamine, mis konkureerib kiirgusliku protsessiga. Et pakkuda välja lahendusi sellele probleemile, tuleb esmalt selgitada selle päritolu ja põhjused. Käesolev töö ongi pühendatud fluorestsentsi kustutamise põhjuste väljaselgitamisele haruldaste muldmetallidega dopeeritud nanoosakestes. Selleks arendati välja nn energiaülekandesondi meetod, mille abil näidati, et fluorestsentsi kustutamist põhjustavad peamiselt vesilahusest pärinevad veemolekulid ja –OH rühmad, mis on märkimisväärses koguses jaotunud üle kogu nanoosakese ruumala, paiknedes tõenäoliselt mesopoorides, mis tekivad materjali kristallisatsiooni käigus.

The development of novel methods for cancer diagnostics is one of the major focus areas for modern medicine. Fluorescence deep tumor imaging may be an efficient non-invasive diagnostics technique. A number of materials suggested to be potential candidates for fluorescence imaging agents. Rare-earth doped nanoparticles are of great interest of this respect, as they are more biocompatible than traditional organic phosphors and quantum dots, photo- and thermally stable. However, the fluorescence properties of these materials need further improvement. The main problem to be overcome in this respect is fluorescence quenching, which competes with the emission process. In order to be able to suggest a way to reduce quenching, one needs to study its causes and origin. This work is devoted to the study of origin of the fluorescence quenching in the rare-earth doped nanoparticles. For this, a so-called energy transfer probing technique was developed. By means of this tool it has been shown that the main source of fluorescence quenching is a significant amount of water molecules and –OH groups, originating from the solvent and distributed in the volume of the nanoparticles, mainly in mesopores formed during the material crystallization.