Upconversion nanoparticles (UCNPs) are widely used as energy donors via a luminescence resonance energy transfer (LRET) technique in biosensing field. To enhance LRET efficiency and afford an improved sensitivity for Cu²⁺ detection, sandwich structured NaYF₄@NaYF₄:Er³⁺/Yb³⁺@NaYF₄ UCNPs have been designed and prepared. For the core-internal shell-external shell structure, luminescence ions (Er³⁺) are located in the internal shell near the nanoparticle surface, which is close enough to energy acceptors outside. To study the sensing properties, the UCNPs are used as energy donors and rhodamine B hydrazide (RBH) as energy acceptors to construct the nanoprobes. It is found that the sandwich structured nanoparticles gains more intense luminescence than the naked NaYF₄:Er³⁺/Yb³⁺ UCNPs, which is beneficial to the further improvement of signal sensitivity in biological detection. Moreover, the specificity for detecting Cu²⁺ is also checked and found that the designed probe is much more sensitive to Cu²⁺ than the other ions including K⁺, Na⁺, Li⁺, Ca²⁺, Ba²⁺, Mg²⁺, Zn²⁺ and Sr²⁺. The experiment on the stability of UCNPs-RBH probe and RBH shows the 980 nm laser produces less photodamage to RBH than that of visible light. Therefore, the UCNPs can be used to construct potential probes for realizing effective detection of Cu²⁺.

在生物传感领域，上转换纳米粒子（UCNPs）通过发光共振能量转移（LRET）技术被广泛用作能量供体。为了提高LRET效率并提高Cu ²⁺检测的灵敏度，已经设计并制备了夹心结构的NaYF ₄ @NaYF ₄：Er ³⁺ / Yb ³⁺ @NaYF ₄ UCNP。对于核-内部壳-外部壳结构，发光离子（Er ³⁺）位于纳米粒子表面附近的内壳中，该内壳足够靠近外部的能量受体。为了研究传感特性，UCNP被用作能量供体，若丹明B酰肼（RBH）被用作能量受体以构建纳米探针。发现夹层结构的纳米颗粒比裸NaYF ₄：Er ³⁺ / Yb ³⁺ UCNPs获得更强的发光，这有利于进一步提高生物检测中的信号灵敏度。此外，还检查了检测Cu ²⁺的特异性，发现设计的探针对Cu ^2+的敏感性比其他离子（包括K ⁺，Na ⁺，Li⁺，Ca 2 ⁺，Ba 2 ⁺，Mg 2 ⁺，Zn ²⁺和Sr ²⁺。UCNPs-RBH探针和RBH的稳定性实验表明，980 nm激光对RBH的光损伤比可见光小。因此，UCNPs可用于构建潜在的探针，以实现对Cu ^2+的有效检测。