Self-referenced photon upconversion nanosensors for imaging applications
Final Report Abstract
In the framework of this project, a variety of Yb3+,Tm3+- and Yb3+,Er3+-co-doped upconversion nanoparticles (UCNPs) and different pH-responsive dyes were prepared with absorption bands closely matching with one of the emission bands of the UCNPs, which are located at 470 nm, 650 nm, and 800 nm for Tm3+-doped UCNPs and at 550 nm and 660 nm for Er3+-doped UCNPs, respectively. The BODIPY dyes and the rosamine dyes prepared for this purpose reveal absorption maxima at 485 nm and 560 nm, emission maxima at about 530 nm and 590 nm, and pH-dependent changes of their fluorescence quantum yields, i.e., a protonationinduced switching ON of their fluorescence. Combining these UCNPs and the pH-responsive dyes in hydrogels provided a versatile platform of inner filter-based sensor systems suitable for the preparation of sensor strips and pads that can be utilized e.g., for the monitoring of the metabolism of bacteria or corrosion processes. Mechanistic studies with RET-based nanosensors revealed some disadvantages of this design concept to be overcome for the next generation of RET-type UCNP nanosensors such as the prevention of the aggregation of surface-coordinated sensor dyes and the choice of a suitable particle size minimizing signal contribution from non-affected single lanthanide emitters in the inner particle core. As a prerequisite for safe in vitro and in vivo applications of UCNPs, different surface coatings, utilizing various organic ligands such as citrate, phosphonate ligands with a different number of phosphonate groups, polyacrylic acid, and amphiphilic poly(maleic acid-alt-1-octadecene), were assessed regarding their potential to stabilize UCNPs under dilute conditions in aqueous environments and prevent particle disintegration, leading to the release of potentially toxic fluoride and lanthanide ions. In this context, also an optical screening method was developed for the evaluation of different surface coatings utilizing the fluorescence decay kinetics and lifetime of the Yb3+ down-converted emission. Method validation was done by quantification of the released lanthanide and fluoride ions with ICP-OES and a fluoride-sensitive ion electrode and TEM studies.
Publications
- Simple Self-Referenced Luminescent pH Sensors Based on Upconversion Nanocrystals and pH-Sensitive Fluorescent BODIPY Dyes, Analytical Chemistry 2019, 91, 7756-7764
Sebastian Radunz, Elina Andresen, Christian Würth, Andrea Koerdt, Harald Rune Tschiche, and Ute Resch-Genger
(See online at https://doi.org/10.1021/acs.analchem.9b01174) - Surface Modifications for Photon-Upconversion-Based Energy-Transfer Nanoprobes, Langmuir 2019, 35, 5093–5113
Elina Andresen, Ute Resch-Genger and Michael Schäferling
(See online at https://doi.org/10.1021/acs.langmuir.9b00238) - Solvothermal Synthesis of Lanthanide-doped NaYF4 Upconversion Crystals with Size and Shape Control - Particle Properties and Growth Mechanism, Chem Nano Mat 2020
Chunning Sun, Michael Schäferling, Ute Resch-Genger, and Michael Gradzielski
(See online at https://doi.org/10.1002/cnma.202000564) - Time-resolved Luminescence Spectroscopy for Monitoring the Stability and Dissolution Behaviour of Upconverting Nanocrystals with Different Surface Coatings, Nanoscale 2020, 12, 12589-12601
Elina Andresen, Christian Würth, Carsten Prinz, Matthias Michaelis and Ute Resch-Genger
(See online at https://doi.org/10.1039/D0NR02931A)
