School of Biomedical Engineering, State Environmental Protection Key Laboratory of Environmental Health Impact Assessment of Emerging Contaminants, Shanghai Jiao Tong University, Shanghai 200240, China.
Key Laboratory of Pollutant Chemistry and Environmental Treatment, School of Chemistry and Environmental Science, Yili Normal University, Yining 835000, China.
Nanoscale. 2022 Jun 16;14(23):8342-8348. doi: 10.1039/d2nr01078j.
Gold nanoclusters (AuNCs), as a novel fluorescent material, have been extensively explored and developed for bioimaging because of their attractive advantages such as ultrasmall size, low toxicity and exceptional two-photon excitation properties. However, it still remains a challenge to produce water-soluble, biocompatible and ultrabright AuNCs. Herein, we report on a novel one-pot synthesis of highly luminescent and biocompatible AuNCs by using polyvinyl pyrrolidone (PVP), a water-soluble polymer, to rigidify the primary stabilizing layer (shell) that is composed of 6-aza-2-thiothymine (ATT) ligands bound to the particle. Such shell-rigidification resulted in a significant enhancement of the fluorescence efficiency, reaching a quantum yield of 39% under the best conditions, about 35-fold increase from the intrinsically weak fluorescence of the AuNCs stabilized by only ATT. The fluorescence enhancement mechanism was systematically characterized, and the results indicate that PVP coating rigidifies the ATT ligand shell through steric hindrance and reduces the nonradiative relaxation of the excited states. The biocompatible PVP-AuNCs were further examined for two-photon cellular and sentinel lymph node (SLN) bioimaging, and we observed pH-dependent cytoplasmic images and intense green fluorescence in SLN and lymphatic vessels.
金纳米簇（AuNCs）作为一种新型荧光材料，因其具有超小尺寸、低毒性和优异的双光子激发特性等吸引人的优点，已被广泛探索和开发用于生物成像。然而，制备具有良好水溶性、生物相容性和超高亮度的 AuNCs 仍然是一个挑战。在此，我们报告了一种通过使用聚乙烯吡咯烷酮（PVP）合成高度发光和生物相容的 AuNCs 的新一锅法。PVP 是一种水溶性聚合物，可刚性化由结合到颗粒上的 6-氮杂-2-硫代胸腺嘧啶（ATT）配体组成的初级稳定层（壳）。这种壳刚性化导致荧光效率显著增强，在最佳条件下达到 39%的量子产率，比仅由 ATT 稳定的 AuNCs 的固有弱荧光提高了约 35 倍。系统地表征了荧光增强机制，结果表明 PVP 涂层通过空间位阻刚性化 ATT 配体壳，并减少了激发态的非辐射弛豫。进一步研究了生物相容的 PVP-AuNCs 进行双光子细胞和前哨淋巴结（SLN）生物成像，我们观察到 pH 依赖性的细胞质图像以及 SLN 和淋巴管中的强烈绿色荧光。
