近日，美国亚利桑那大学的Judith Su及其研究团队取得一项新进展。经过不懈努力，他们利用微环面光学谐振器光热显微镜实现单个5nm量子点的检测。相关研究成果已于2024年8月19日在国际知名学术期刊《光：科学与应用》上发表。

本研究将微型环形谐振器与光热显微镜结合，以空间分辨率检测直径5纳米的单量子点（QD），信噪比超过10⁴。光热图像是通过泵浦激光逐点扫描生成的。通过高灵敏度荧光成像证实了18纳米量子点的单粒子检测，通过与理论比较证实了5纳米量子点的单粒子检测。这一系统展示出检测最小热耗散0.75皮瓦的能力。

为了实现这一点，研究人员将基于微型环形谐振器的光热显微镜装置与低振幅调制泵浦激光相结合，并利用比例-积分-微分控制器输出作为光热信号源，以降低噪声并提高信号稳定性。这些量子点的热耗散低于单个染料分子的热耗散。研究人员预计，这项研究工作将在生物学、纳米技术、材料科学、化学和医学等众多领域得到应用。

据悉，无标记的单颗粒和分子检测技术在基础科学、疾病诊断和纳米材料研究中发挥着重要作用。尽管基于荧光的方法可用于单分子检测和成像，但其应用受限于可用的分子探针以及光闪烁和光漂白现象。光热显微镜作为一种无标记成像技术应运而生，它能够以高灵敏度检测单个纳米吸收体。

回音壁模式（WGM）微谐振器可将光限制在小体积内，以增强光与物质的相互作用，因此是一个有前景的超灵敏光热显微镜平台。此前，微型环形光学谐振器已与光热显微镜结合，用于检测长250纳米的金纳米棒和长100纳米的聚合物。

附：英文原文

Title: Single 5-nm quantum dot detection via microtoroid optical resonator photothermal microscopy

Author: Hao, Shuang, Suebka, Sartanee, Su, Judith

Issue&Volume: 2024-08-19

Abstract: Label-free detection techniques for single particles and molecules play an important role in basic science, disease diagnostics, and nanomaterial investigations. While fluorescence-based methods are tools for single molecule detection and imaging, they are limited by available molecular probes and photoblinking and photobleaching. Photothermal microscopy has emerged as a label-free imaging technique capable of detecting individual nanoabsorbers with high sensitivity. Whispering gallery mode (WGM) microresonators can confine light in a small volume for enhanced light-matter interaction and thus are a promising ultra-sensitive photothermal microscopy platform. Previously, microtoroid optical resonators were combined with photothermal microscopy to detect 250nm long gold nanorods and 100nm long polymers. Here, we combine microtoroids with photothermal microscopy to spatially detect single 5nm diameter quantum dots (QDs) with a signal-to-noise ratio exceeding 10⁴. Photothermal images were generated by point-by-point scanning of the pump laser. Single particle detection was confirmed for 18nm QDs by high sensitivity fluorescence imaging and for 5nm QDs via comparison with theory. Our system demonstrates the capability to detect a minimum heat dissipation of 0.75pW. To achieve this, we integrated our microtoroid based photothermal microscopy setup with a low amplitude modulated pump laser and utilized the proportional-integral-derivative controller output as the photothermal signal source to reduce noise and enhance signal stability. The heat dissipation of these QDs is below that from single dye molecules. We anticipate that our work will have application in a wide variety of fields, including the biological sciences, nanotechnology, materials science, chemistry, and medicine.

DOI: 10.1038/s41377-024-01536-9

Source: https://www.nature.com/articles/s41377-024-01536-9