Self-referenced photon upconversion nanosensors for imaging applications

上转换纳米材料是一种掺杂稀土离子的光致发光无机纳米晶体，可以将红外辐射转化为可见光。它们可以用聚合物外壳和不同的（生物）分子配体、染料和指示剂进行表面功能化，这使得它们可以用于各种生物分析和传感应用。与目前使用的发光探针相比，它们具有几个优点，例如消除自身荧光，多色发射和卓越的光稳定性，从而能够开发新的和改进许多现有应用。然而，它们在化学传感器或用于化学成像的纳米探针中的应用是一个相对未开发的领域。在这个应用中，提出利用上转换纳米粒子（UCNPs）与分析敏感染料（指示剂）结合作为一类新的自参考纳米探针，具有改进的光稳定性，用于比例细胞内传感和成像。因此，UCNPs作为发光供体，而耦合到粒子表面的指示器作为受体。将评估不同的感应机制，如由于共振能量转移或发射-再吸收机制引起的指示剂的敏化发射，其中UCNP发射通过内部过滤效应被分析物诱导的指示剂吸收变化调制。目的是制备和评价纳米探针用于测定氧、pH和Ca2+，这是细胞代谢和功能障碍的关键参数。合理开发基于ucnp的纳米探针的一个关键因素是研究环境因素（如水或重金属分子的猝灭）对相关电子跃迁的干扰，以及如何通过适当的表面涂层将这些干扰降至最低。因此，该项目还将包括光谱表征，包括发射状态的寿命测量及其对外部刺激和FRET过程的响应。

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.