Sensing and characterizing water-soluble polypeptides are essential in various biological applications. However, detecting polypeptides using Surface-Enhanced Raman Scattering (SERS) remains a challenge due to the dominance of aromatic amino acid residues and backbones in the signal, which hinders the detection of non-aromatic amino acid residues. Herein, intra-nanoparticle plasmonic nanogap were designed by etching the Ag shell in Au@AgNPs (i.e., obtaining AuAg cores) with chlorauric acid under mild conditions, at the same time forming the outermost Au shell and the void between the AuAg cores and the Au shell (AuAg@void@Au). By varying the Ag to added chloroauric acid molar ratios, we pioneered a simple, controllable, and general synthetic strategy to form interlayer-free nanoparticles with tunable Au shell thickness, achieving precise regulation of electric field enhancement within the intra-nanogap. As validation, two polypeptide molecules, bacitracin and insulin B, were successfully synchronously encapsulated and spatial-confined in the intra-nanogap for sensing. Compared with concentrated 50 nm AuNPs and Au@AgNPs as SERS substrates, our simultaneous detection method improved the sensitivity of the assay while benefiting to obtain more comprehensive characteristic peaks of polypeptides. The synthetic strategy of confining analytes while fabricating plasmonic nanostructures enables the diffusion of target molecules into the nanogap in a highly specific and sensitive manner, providing the majority of the functionality required to achieve peptide detection or sequencing without the hassle of labeling.

中文翻译：

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基于纳米粒子内等离子体纳米间隙的多肽空间限制 SERS 分析

感测和表征水溶性多肽在各种生物应用中至关重要。然而，使用表面增强拉曼散射（SERS）检测多肽仍然是一个挑战，因为信号中芳香族氨基酸残基和主链占主导地位，这阻碍了非芳香族氨基酸残基的检测。本文通过在温和条件下用氯金酸蚀刻Au@AgNPs中的Ag壳（即获得AuAg核）来设计纳米粒子内等离子体纳米间隙，同时形成最外层的Au壳以及AuAg核与AuAg核之间的空隙。金壳（AuAg@void@Au）。通过改变Ag与添加的氯金酸的摩尔比，我们首创了一种简单、可控、通用的合成策略，形成具有可调Au壳厚度的无层间纳米粒子，实现了纳米间隙内电场增强的精确调控。作为验证，两种多肽分子杆菌肽和胰岛素 B 被成功同步封装并空间限制在纳米间隙内进行传感。与浓缩的50 nm AuNPs和Au@AgNPs作为SERS底物相比，我们的同步检测方法提高了测定的灵敏度，同时有利于获得更全面的多肽特征峰。在制造等离子体纳米结构时限制分析物的合成策略使目标分子能够以高度特异性和灵敏的方式扩散到纳米间隙中，从而提供实现肽检测或测序所需的大部分功能，而无需标记的麻烦。