Ultrasmall gold nanoclusters (AuNCs) with distinct photoluminescence properties are promising fluorophores for optical applications. However, it remains a great challenge to precisely modulate their near-infrared (NIR) fluorescence properties via a simple yet efficient strategy. Herein, we report a new, surface tailoring strategy for effectively modulating the NIR fluorescence property of AuNCs by harnessing the attractive property of metal-organic frameworks. With zeolite imidazolate frameworks-8 (ZIF-8) as the example, we showed that highly fluorescent AuNCs can be in situ encapsulated into ZIF-8 via a one-pot reaction, yielding AuNCs@ZIF-8 composites with enhanced NIR fluorescence intensity. Particularly, AuNCs@ZIF-8 composites exhibit an emission maximum at 830 nm, which is 190 nm longer than the emission wavelength of AuNCs without the ZIF-8 encapsulation. Mechanism studies based on fluorescence decay spectra and X-ray photoelectron spectroscopy revealed that ZIF-8 mainly poses a significant effect on the ligand-metal charge transfer process of AuNCs due to the confinement effect. By incorporating Rhodamine B (RhB) into NIR-emitting AuNCs@ZIF-8 composites, we established a ratiometric fluorescent sensing platform for the detection of acetylcholinesterase (AChE) based on the turn-on fluorescence response of AuNCs towards thiolates. The AuNCs@ZIF-8/RhB system exhibits a high sensitivity with a detection limit of 0.4 mU/mL and good specificity towards common biological interferences. Moreover, the present ratiometric fluorescence assay shows good recovery for AChE detection in human serum, suggesting its potential application for real sample analysis. Finally, the fluorescence response mechanism of both AuNCs@ZIF-8 and AuNCs towards AChE is elucidated by fluorescence lifetime analysis and density functional theory (DFT) calculation. This study demonstrates the feasibility of modulating the NIR fluorescence property of AuNCs by MOF-based surface tailoring strategy towards enhanced biosensing application.

具有独特光致发光特性的超小金纳米团簇 (AuNC) 是用于光学应用的有前途的荧光团。然而，通过简单而有效的策略精确调节其近红外 (NIR) 荧光特性仍然是一个巨大的挑战。在此，我们报告了一种新的表面定制策略，可通过利用金属有机框架的吸引力来有效调节 AuNC 的 NIR 荧光特性。以沸石咪唑酯骨架-8 (ZIF-8) 为例，我们表明高荧光 AuNCs 可以通过一锅反应原位封装到 ZIF-8 中，产生具有增强的 NIR 荧光强度的 AuNCs@ZIF-8 复合材料。特别是，AuNCs@ZIF-8 复合材料在 830 nm 处表现出最大发射，这比没有 ZIF-8 封装的 AuNC 的发射波长长 190 nm。基于荧光衰减光谱和 X 射线光电子能谱的机理研究表明，由于限制效应，ZIF-8 主要对 AuNC 的配体-金属电荷转移过程产生显着影响。通过将罗丹明 B (RhB) 掺入 NIR 发射 AuNCs@ZIF-8 复合材料中，我们建立了一个比率荧光传感平台，用于检测基于 AuNC 对硫醇盐的开启荧光响应的乙酰胆碱酯酶 (AChE)。AuNCs@ZIF-8/RhB 系统具有高灵敏度，检测限为 0.4 mU/mL，对常见的生物干扰具有良好的特异性。此外，本比率荧光测定显示出人血清中 AChE 检测的良好回收率，表明其在实际样品分析中的潜在应用。最后，通过荧光寿命分析和密度泛函理论 (DFT) 计算阐明了 AuNCs@ZIF-8 和 AuNCs 对 AChE 的荧光响应机制。本研究证明了通过基于 MOF 的表面定制策略调节 AuNC 的 NIR 荧光特性以增强生物传感应用的可行性。