Cheng Ting, Marin Riccardo, Skripka Artiom, Vetrone Fiorenzo
Centre Énergie, Matériaux et Télécommunications , Institut National de la Recherche Scientifique, Université du Québec , Varennes , Quebec J3X 1S2 , Canada.
J Am Chem Soc. 2018 Oct 10;140(40):12890-12899. doi: 10.1021/jacs.8b07086. Epub 2018 Sep 28.
In the context of light-mediated tumor treatment, the application of ultraviolet (UV) radiation can initiate drug release and photodynamic therapy. However, its limited penetration depth in tissues impedes the subcutaneous applicability of such radiation. On the contrary, near-infrared (NIR) light is not energetic enough to initiate secondary photochemical processes, but can pierce tissues at a significantly greater depth. Upconverting nanoparticles (UCNPs) unify the advantages of both extremes of the optical spectrum, they can be excited by NIR irradiation and emit UV light through the process of upconversion, effective NIR-to-UV generation being attained with UCNPs as large as 100 nm. However, in anticipation of biomedical applications, the size of UCNPs must be greatly minimized to favor their cellular internalization; yet straightforward size reduction negatively affects the NIR-to-UV upconversion efficiency. Herein, we propose a two-step strategy to obtain small yet bright lithium-based UCNPs. First, we synthesized UCNPs as small as 5 nm by controlling the relative amount of coordinating ligands, namely oleylamine (OM) and oleic acid (OA). Although these UCNPs were chemically unstable, particle coarsening via an annealing process in the presence of fresh OA yielded structurally stable and highly monodisperse sub-10 nm crystals. Second, we grew a shell with controlled thickness on these stabilized cores of UCNPs, improving the NIR-to-UV upconversion by orders of magnitude. Particularly in the case of LiYbF:Tm/LiYF UCNPs, their NIR-to-UV upconversion surpassed the gold standard 90 nm-sized LiYF:Tm, Yb UCNPs. All in all, these UCNPs show great potential within the biomedical framework as they successfully combine the requirements of small size, deep tissue NIR penetration and bright UV emission.
在光介导的肿瘤治疗背景下，紫外线（UV）辐射的应用可引发药物释放和光动力疗法。然而，其在组织中的穿透深度有限，阻碍了这种辐射在皮下的适用性。相反，近红外（NIR）光能量不足以引发二次光化学过程，但能穿透更深的组织。上转换纳米粒子（UCNPs）兼具光谱两端的优势，它们可被近红外辐射激发，并通过上转换过程发射紫外线，尺寸达100 nm的UCNPs也能实现有效的近红外到紫外线的转换。然而，考虑到生物医学应用，必须大幅减小UCNPs的尺寸以利于其细胞内化；然而直接减小尺寸会对近红外到紫外线的上转换效率产生负面影响。在此，我们提出一种两步策略来获得小尺寸且发光强的锂基UCNPs。首先，我们通过控制配位配体（油胺（OM）和油酸（OA））的相对量，合成了小至5 nm的UCNPs。尽管这些UCNPs化学性质不稳定，但在新鲜OA存在下通过退火过程使颗粒粗化，得到结构稳定且高度单分散的亚10 nm晶体。其次，我们在这些稳定的UCNPs核上生长具有可控厚度的壳层，将近红外到紫外线的上转换提高了几个数量级。特别是对于LiYbF:Tm/LiYF UCNPs，它们的近红外到紫外线的上转换超过了90 nm尺寸的金标准LiYF:Tm, Yb UCNPs。总而言之，这些UCNPs在生物医学框架内显示出巨大潜力，因为它们成功地结合了小尺寸、深层组织近红外穿透和明亮紫外线发射的要求。
