上转换纳米材料由于其特殊的光学性能，已被广泛应用于荧光探针、生物成像、生物分子检测等生命科学领域。然而，怎样将上转换纳米材料由荧光工具变成光动力治疗工具，还是一个急需探索的课题。纳米二氧化钛是一种广泛使用的光触媒材料，其在紫外光激发下可以产生自由基，已用于体外杀菌和有机物降解等诸多领域。但由于紫外光对人体的毒副作用和穿透性差等缺点，如何将其用于活体组织做纳米药物，也是一个挑战。在本项目中，我们拟将上转换材料和二氧化钛进行有效复合，互相取长补短，共同构建成新型的纳米光触媒及纳米药物。这种材料可使用近红外光照射，通过上转换过程产生紫外光且被二氧化钛吸收而产生自由基，从而可用于生物深层组织的光动力治疗，提高传统光动力疗法的作用深度和范围。而且，自由基的杀毒能力也强于传统的单态氧。另一方面，这种复合的光触媒材料，可利用太阳光中的红外波段的光，也将有望提高人们对太阳能的利用效率。

Owing to their unique optical properties, upconversion nanocrystals have been widely used in biological science such as biolabels, imaging and detection of biomolecules. However, it is still rarely explored that how to harness these fluorescent tools for therapy applications. TiO2 is a widely used photocatalyst for sterilization and degradation of organice pollution, due to generation of free radicals upon UV irradiation. But it is a big challenge to apply it for in-vivo biological system as nanomedicines, because of the phototoxicity and low penetration depth of UV light. In this project, we bring forward an idea to produce new kinds of photocatalysts and nanomedicines which consist of upconversion nanocrystals and TiO2. These materials will combine the merits from both types of materials and overcome their inherent stortcomings. Upon the excitation of NIR light, these materials can give free radicals from TiO2 through upconverting the NIR photons to UV photons. As such, this kind of materials will be applicable to deep biological tissue and improve photodynamic therapy effect. Furthermore, the generated free radicals from the nanocomposites are stronger oxdizers than singlet oxygen from tranditional photosensitizers. On the other hand, these nanocomposites also possess great potential to enhance the utilization efficiency of solar energy when they are used as NIR photocatalysts.