Nanogaps as “hot spots” with highly localized surface plasmon can generate ultrastrong electromagnetic fields. Superior to the exterior nanogaps obtained via aggregation and self-assembly, interior nanogaps within Au and Ag nanostructures give stable and reproducible surface-enhanced Raman scattering (SERS) signals. However, the synthesis of nanostructures with interior hot spots is still challenging because of the lack of high-yield strategies and clear design principles. Herein, gold–silver nanoclusters (Au–Ag NCs) with multiple interior hot spots were fabricated as SERS platforms via selective growth of Ag nanoparticles on the tips of Au nanostars (Au NSs). Furthermore, the interior gap sizes of Au–Ag NCs can be facilely tuned by changing the amount of AgNO₃ used. Upon 785 nm excitation, single Au–Ag NC₃₅₀ exhibits 43-fold larger SERS enhancement factor and the optimal signal reproducibility relative to single Au NS. The SERS enhancement factors and signal reproducibility of Au–Ag NCs increase with the decrease of gap sizes. Collectively, the Au–Ag NCs could serve as a flexible, reproducible, and active platform for SERS investigation.

中文翻译：

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纳米级金在表面上选择性拉长银，以增强表面拉曼散射

纳米间隙是具有高度局部化的表面等离子体激元的“热点”，可以产生超强电磁场。优于通过聚集和自组装获得的外部纳米间隙，Au和Ag纳米结构内的内部纳米间隙可提供稳定且可重现的表面增强拉曼散射（SERS）信号。然而，由于缺乏高产率策略和清晰的设计原理，具有内部热点的纳米结构的合成仍然具有挑战性。在此，通过在Au纳米星（Au NSs）的尖端选择性生长Ag纳米粒子，将具有多个内部热点的金银纳米簇（Au-Ag NCs）制成SERS平台。此外，可以通过更改AgNO _3的使用量来轻松调整Au-Ag NCs的内部间隙尺寸。在785 nm激发下，单Au-Ag NC₃₅₀具有相对于单个Au NS而言大43倍的SERS增强因子和最佳信号重现性。Au-Ag NCs的SERS增强因子和信号重现性随间隙大小的减小而增加。总体而言，Au-Ag NC可以作为SERS研究的灵活，可重现和活跃的平台。