Self-referenced photon upconversion nanosensors for imaging applications

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Self-referenced photon upconversion nanosensors for imaging applications Upconverting nanomaterials are photoluminescent inorganic nanocrystals doped with rare earth ions that can convert infrared radiation into visible light. They can be surface-functionalized with polymeric shells and different (bio)molecular ligands, dyes, and indicators, which allows their use in various bioanalytical and sensing applications. They possess several advantages over currently used luminescent probes such as elimination of autofluorescence, multicolor emission, and exceptional photostability, thus enabling the development of new and the improvement of numerous existing applications. However, their use in chemical sensors or nanoprobes for chemical imaging is a comparatively unexplored field. In this application the utilization of upconversion nanoprarticles (UCNPs) in combination with analyte-sensitive dyes (indicators) as a new class of self-referenced nanoprobes with improved photostability for ratiometric intracellular sensing and imaging is proposed. Thereby, the UCNPs act as light emitting donors and the indicators coupled to the particle surface as acceptors. Different sensing mechanisms will be assessed such as sensitized emission of the indicator due to a resonance energy transfer or an emission-reabsorption mechanism, where the UCNP emission is modulated by analyte-induced changes in the indicator absorption via an inner filter effect. The aim is the preparation and evaluation of nanoprobes for the determination of oxygen, pH and Ca2+, which are key parameters of cellular metabolism and dysfunctions. A crucial factor for the rational development of UCNP-based nanoprobes is the study of interferences on the involved electronic transitions by environmental factors (e.g. quenching by water or heavy metal molecules) and how these interferences can be minimized by appropriate surface coatings. Therefore, this project will also include spectroscopic characterizations including lifetime measurements of the emissive states and their responses to external stimuli and FRET processes.