We propose a scheme of exploring the kinetic properties of the receptor-ligand binding process by means of the frequency stability measurement of a whispering-gallery-mode optical microcavity. In this scheme, the probe beam is directly locked to the microcavity and the time resolution of the sensing detection is determined by the feedback loop response time $10\mu \mathrm{s}$, which is much shorter than the current limit of about 20 ms. The receptor-ligand interactions are entirely mapped onto the probe light frequency and can be recovered through the analysis of its Allan deviation. As a result, one can investigate a chemical and biological reaction at the single-molecule level without the need for resolving the occurrence and duration of individual binding events. We numerically study this sensing scheme based on a practical optoplasmonic platform, where several gold nanorods are adsorbed onto the surface of a spherical microcavity that is located in the aqueous environment. The microsphere has a typical radius of $40\mu \mathrm{m}$ and quality factor of ${10}^6$ (finesse of $2.6\times {10}^3$) at the wavelength of 785 nm. This powerful scheme may extend single-molecule sensing to the kinetic regime of the biochemical reactions.

中文翻译：

---

艾伦偏差说明了耳语画廊模式光学微腔在单分子传感中的结合特性

我们提出了一种通过耳语画廊模式光学微腔的频率稳定性测量来探索受体-配体结合过程动力学特性的方案。在这种方案中，探测光束直接锁定在微腔上，传感检测的时间分辨率取决于反馈回路的响应时间。$10\mu \mathrm{s}$，比目前大约20毫秒的限制短很多。受体-配体相互作用完全映射到探针光频率上，并且可以通过分析其Allan偏差来恢复。结果，人们可以研究单分子水平的化学和生物反应，而无需解决单个结合事件的发生和持续时间。我们基于实用的光等离子体平台对这种传感方案进行了数值研究，其中几个金纳米棒被吸附到位于水环境中的球形微腔表面上。微球的典型半径为$40\mu \mathrm{米}$ 和品质因数 ${10}^6$ （的精细度 $2.6\times {10}^3$）在785 nm的波长处。这种强大的方案可以将单分子传感扩展到生化反应的动力学机制。