Trace detection of chiral molecules, which is of great significance in chemical, biological, medical and pharmaceutical sciences, requires microscopic techniques at the single-particle or single-molecule level. Although ensemble experiments show that the circular dichroism of chiral molecules can be amplified by plasmonic nanocrystals, trace detection of small chiral molecules remains challenging due to weak signals that are far below the detection limit. Herein, we demonstrate trace detection of chiral J-aggregated molecules adsorbed on individual Au nanorods (NRs) using single-particle circular differential scattering (CDS) spectroscopy. Through measuring the single-particle CDS spectra, we identified dip–peak bisignatures and further determined the chirality by matching them with calculations modelled with chiral media. We therefore find that plasmonic nanocrystals can dramatically amplify the circular dichroism of strongly coupled molecules to a detectable level so that the detection limit is as low as 3.9 × 10³ molecules on an individual plasmonic nanoparticle, whereas 2.5 × 10¹² molecules free in solution are barely detectable using a commercial circular dichroism instrument, suggesting a significant amplification factor of 10⁸. Our method provides a promising strategy with a high amplification factor, shedding light on the trace detection of chiral molecules using optical microscopic methods.

中文翻译：

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单金纳米棒上吸附的手性 J 聚集分子的痕量检测

手性分子的痕量检测在化学、生物、医学和制药科学中具有重要意义，需要单颗粒或单分子水平的显微技术。尽管集合实验表明，等离激元纳米晶体可以放大手性分子的圆二色性，但由于远低于检测限的微弱信号，小手性分子的痕量检测仍然具有挑战性。在此，我们展示了使用单颗粒圆差示散射（CDS）光谱对吸附在单个金纳米棒（NR）上的手性 J 聚集分子进行痕量检测。通过测量单粒子 CDS 光谱，我们识别了谷峰双特征，并通过将它们与手性介质建模的计算相匹配来进一步确定手性。单个等离子体纳米粒子上有^{3 个}分子，而使用商用圆二色性仪器几乎无法检测到溶液中游离的^{2.5 × 10 12 个分子，这表明放大系数为 10 8}。我们的方法提供了一种具有高放大系数的有前途的策略，为使用光学显微方法进行手性分子的痕量检测提供了线索。