受激发射损耗(STED)显微镜的性能关键取决于荧光探针。超小型Au纳米团簇(AuNC)表现出大的斯托克斯位移,和良好的受激发射响应,这可能对STED成像有用。然而,AuNCs在尺寸上是多分散的,对周围环境敏感,难以控制表面官能团的化学计量,这导致生物结构标记的密度降低和高度异质性。这里,通过开发一种用DNA笼封装超小AuNC的方法来克服这一限制,产生单分散的,和长期稳定的单官能化AuNC。此外,DNA笼统也大大提高了AuNCs的荧光量子产率和光稳定性。在STED成像中,DNA笼状的AuNC产生约40nm的空间分辨率,并且能够以良好的标记密度和均匀性解析微管线形状。相比之下,没有笼子,AuNCs-DNA缀合物仅达到约55nm分辨率并产生斑点,分辨率差的微管结构,由于聚集体的存在。总的来说,开发了一种实现精确表面官能化并大大提高单分散性的方法,稳定性,以及AuNCs的光学性质,为STED成像提供了一类有前途的荧光探针。
The performance of Stimulated Emission Depletion (STED) microscopy depends critically on the fluorescent probe. Ultrasmall Au nanoclusters (Au NCs) exhibit large Stokes shift, and good stimulated emission response, which are potentially useful for STED imaging. However, Au NCs are polydispersed in size, sensitive to the surrounding environment, and difficult to control surface functional group stoichiometry, which results in reduced density and high heterogeneity in the labeling of biological structures. Here, this limitation is overcome by developing a method to encapsulate ultrasmall Au NCs with DNA cages, which yielded monodispersed, and monofunctionalized Au NCs that are long-term stable. Moreover, the DNA-caging also greatly improved the fluorescence quantum yield and photostability of Au NCs. In STED imaging, the DNA-caged Au NCs yielded ≈40 nm spatial resolution and are able to resolve microtubule line shapes with good labeling density and homogeneity. In contrast, without caging, the Au NCs-DNA conjugates only achieved ≈55 nm resolution and yielded spotted, poorly resolved microtubule structures, due to the presence of aggregates. Overall, a method is developed to achieve precise surface functionalization and greatly improve the monodispersity, stability, as well as optical properties of Au NCs, providing a promising class of fluorescent probes for STED imaging.