Detection of the Cu²⁺ ions is crucial because of its environmental and biological implications. The fluorescent-based organic sensors are not suitable for Cu²⁺ detection due to their short penetration depth caused by the UV/visible excitation source. Therefore, we have demonstrated a highly sensitive and selective near-infrared (NIR) excitable poly(acrylic acid) (PAA) coated upconversion nanoparticles (UCNPs) based sensor for Cu²⁺ detection. We construct the PAA modified Na(Yb, Nd)F₄@Na(Yb, Gd)F₄:Tm@NaGdF₄ core-shell-shell structured UCNPs based sensor via a co-precipitation route. The upconversion emission intensity of the PAA-UCNPs decreases linearly with the increase in the Cu²⁺ concentration from 0.125 to 3.125 μM due to the copper carboxylate complex formation between Cu²⁺ and PAA-UCNPs. The calculated detection limit of the PAA-UCNPs based sensor is 0.1 μM. The PAA-UCNPs based sensor is very sensitive and selective toward detecting the Cu²⁺ ions, even when the Cu²⁺ co-exist with other metal ions. The EDTA addition has significantly reversed the upconversion emission quenching by forming the EDTA-Cu²⁺ complex based on their greater affinity toward the Cu²⁺. Therefore, the PAA-UCNPs based sensor can be a promising candidate for Cu²⁺ detection because of their higher sensitivity and selectivity under 980 nm NIR excitation.

由于其对环境和生物学的影响，Cu ²⁺离子的检测至关重要。基于荧光的有机传感器由于UV /可见光激发源引起的穿透深度短，因此不适合用于Cu ²⁺检测。因此，我们已经证明了基于高灵敏度和选择性的近红外（NIR）可激发聚（丙烯酸）（PAA）涂层的上转换纳米粒子（UCNPs）为基础的传感器，用于Cu ²⁺检测。我们通过共沉淀途径构建了PAA修饰的Na（Yb，Nd）F ₄ @Na（Yb，Gd）F ₄：Tm @ NaGdF ₄核-壳-壳结构的UCNPs传感器。PAA-UCNPs的上转换发射强度随Cu的增加呈线性下降由于Cu ²⁺和PAA-UCNP之间形成了羧酸铜络合物，因此^2+的浓度为0.125至3.125μM。基于PAA-UCNPs的传感器的计算检出限为0.1μM。即使当Cu ²⁺与其他金属离子共存时，基于PAA-UCNPs的传感器对检测Cu ²⁺离子也非常灵敏和选择性。EDTA的加入通过形成EDTA-Cu ²⁺络合物（基于其对Cu ²⁺的更大亲和力）而显着逆转了上转换发射猝灭。因此，基于PAA-UCNPs的传感器由于在980 nm NIR激发下具有更高的灵敏度和选择性，因此可能成为Cu ²⁺检测的有前途的候选者。