Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable attentions in the area of molecular imaging, targeted therapy and diagnosis. The UCNPs synthesized by conventional methods are usually hydrophobic and require additional surface modification to give them water solubility and biocompatibility. Herein, we designed a simple and convenient strategy for the direct synthesis of water-soluble and biocompatible lanthanum-doped UCNPs through a one-pot reaction without further purification and screening. The doping amount of lanthanide can be adjusted by simply changing the proportion of precursor in the reaction solution. The resulting water-soluble UCNPs possess excellent colloidal stability in physiological media. Under 980 nm excitation, NaGdF₄:Yb³⁺/Er³⁺ and NaGdF₄:Yb³⁺/Tm³⁺ nanoparticles exhibited a dominant green emission band (⁴S_3/2→⁴I_15/2) of Er³⁺ and a dominant blue emission band (¹G₄→³H₆) of Tm³⁺, respectively. Toxic response was not observed with concentration up to 50 mg/L. The hemolysis to rabbit red blood cells was less than 2% in the concentration up to 20 mg/L. The NaGdF₄:Yb³⁺/Er³⁺ nanoparticles exhibited a high r₁ relaxivity of 4.7 mM^-1s^-1, demonstrating that the water-soluble and biocompatible UCNPs can be efficient T₁ contrast agents. The in vivo results show that UCNPs exhibit excellent T₁-weighted imaging and fluorescence imaging abilities simultaneously, and can be used as a versatile promising theranostic nanoplatform.

镧系元素掺杂的上转换纳米颗粒（UCNPs）在分子成像，靶向治疗和诊断领域引起了相当大的关注。通过常规方法合成的UCNP通常是疏水的，并且需要额外的表面修饰以使其具有水溶性和生物相容性。本文中，我们设计了一种简单便捷的策略，可通过一锅法反应直接合成水溶性和生物相容性镧掺杂的UCNP，而无需进一步纯化和筛选。镧系元素的掺杂量可以通过简单地改变反应溶液中的前体的比例来调整。所得的水溶性UCNP在生理介质中具有优异的胶体稳定性。在980 nm激发下，NaGdF ₄：Yb ³⁺ / Er³⁺和NaGdF ₄：Yb ³⁺ / Tm ³⁺纳米粒子表现出Er ³⁺的主要绿色发射带（⁴ S _3/2 → ⁴ I _15/2）和主要的蓝色发射带（¹ G ₄ → ³ H ₆）分别为Tm ³⁺。浓度高达50 mg / L时未观察到毒性反应。浓度高达20 mg / L时，对兔红细胞的溶血率低于2％。NaGdF ₄：Yb ³⁺ / Er ³⁺纳米粒子表现出较高的r ₁弛豫度为4.7 mM ^-1 s ^-1，表明水溶性和生物相容性UCNPs可以是有效的T ₁造影剂。该体内结果显示，UCNPs表现出优异的Ť ₁同时加权成像和荧光成像的能力，并可以用作一个通用的有前途的治疗诊断纳米平台。