鑽石舞台

活細胞標記在評價細胞功能、實時研究細胞過程等方面具有重要意義。Cu(I)催化疊氮-炔環加成（CuAAC）作為一種反應條件溫和、高產率、高選擇性的生物正交點擊化學反應，成為活細胞標記的重要方法之一。目前用於CuAAC的Cu(I)基催化劑主要有兩類：Cu(I)配合物和大尺寸Cu納米顆粒(NPs)。然而，二者均具有較高的細胞毒性。此外，Cu(I)配合物循環性差，Cu NPs反應活性低、選擇性差。因此，迫切需要開發一種具有良好生物相容性和高效率的Cu(I)基催化劑，通過CuAAC實現活細胞標記。

原子精確的金屬納米糰簇(NCs)作為連接金屬單原子和大尺寸金屬納米顆粒（NPs）的橋樑，由於其豐富而可定製的表面化學特性、超小尺寸(通常<2 nm)等優勢，成為一種新型功能材料被廣泛應用於催化、傳感、生物醫學等各種領域。因此設想具有Cu(0)@Cu(I)-硫醇「核-殼結構」的Cu NCs可作為Cu(I)配合物和Cu NPs之間的橋接，成為CuAAC活細胞標記中良好的催化劑。然而，具有原子精度的CuNCs在合成方面仍面臨重大挑戰。因此，我們報道了一種新型的水溶性Cu30NCs的合成方法，合成策略的關鍵是在傳統的NaBH4還原體系中引入NaOH和乙醇，在降低NaBH4還原能力的同時，增強了游離硫醇配體的刻蝕能力，從而實現了原子精度高、穩定性好、產率高的Cu NCs的形成。此外，合成的Cu30(MBA)16NCs具有良好的穩定性，表面Cu(I)物種比例高，對一系列疊氮-炔環加成反應表現出優異的催化性能和良好的循環性。同時，該Cu30 NCs具有良好的生物相容性，作為優良的CuAAC催化劑成功實現了活細胞標記。

Scheme 1 Schematic illustration of the synthesis of water-soluble Cu30(MBA)16 NCs by a modified NaOH-mediated NaBH4 reduction method.

Figure 1 (a) UV-vis absorption spectrum and digital photograph (inset), (b) representative TEM image, (c) ESI-MS spectrum and isotope patterns (inset, black curve; the red curve is the theoretical isotope pattern) of the as-synthesized Cu30(MBA)16 NCs. (d) XPS spectra of Cu 2p3/2 of MBA-Cu(I) complexes (red curve, prepared by mixing CuSO4 with MBA), as-synthesized Cu30(MBA)16 NCs (black curve), and Cu(0) film (blue curve).

Figure 2 (a) Cytotoxicity Cu30 NCs on HeLa cells evaluated by MTT assay after 24 h treatment. Ultrapure water was used as the (negative) control, and Tween 20 was employed as the positive control. Each value represents the relative viability compared to that of untreated cells. Each data point represents an average of four samples and the error bars indicate one standard deviation from the mean. (b)‒(d) Luminescence microscope images of viable cells stained with acetomethoxy derivate of calcein (green color) and non-viable cells stained with ethidium homodimer 1 (red color) after 24 h treatment with the Cu30 NCs.

Figure 3 (a) Schematic illustration on the cell labeling via CuAAC in the presence of Cu NCs as molecular catalyst.Confocal luminescence microscopic images of the pretreated HeLa cells with Ac4ManNAz that were cultured (b) in the presence of RB-PEG2000-Alkyne (10 μM) and Cu30 NCs (20 μM) for 8 h, and (c) in the presence of RB-PEG2000-Alkyne (10 μM) for 24 h. Note: the DAPI dye was used to stain the nucleus of HeLa cells.

G. Yang, Y. Xie, Y. Wang, et al. Water-soluble Cu30 nanoclusters as a click chemistry catalyst for living cell labeling via azide-alkyne cycloaddition. Nano Research. https://doi.org/10.1007/s12274-022-4821-5.

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