Optical microcavities empowered biochemical sensing

Optical microcavities, which are distinguished by their high-quality factors and compact mode volumes, play a crucial role across various sectors, such as microlasers, systems with broken symmetry, optical frequency combs, and optical sensing. Particularly noteworthy is their application in biochemical sensing, where microcavities enhance photon lifetimes and increase the optical field's energy density, fostering robust light-matter interactions that boost sensitivity and reduce detection thresholds. Drawing from the significant benefits of optical microcavities and the swift progress in biochemical sensing, this review offers a detailed examination of optical microcavity-based biochemical sensors, structured into four main sections: sensing mechanisms, structural designs, cutting-edge biochemical sensors, and future outlooks. The review starts by dissecting key microcavity characteristics and discusses predominant and notable sensing mechanisms. These mechanisms encompass mode shift/splitting/broadening, enhancements in lasing and gain, surface plasmon resonance, fluorescence resonance energy transfer, optical frequency comb spectroscopy, optomechanical interactions, and exceptional points, as covered in the mechanism section. Subsequently, we delve into significant optical microcavity structures, including the Fabry-Perot structure, whispering-gallery-mode structure, photonic crystal, and on-chip microring resonator, detailing both foundational and functional microcavity materials along with their fabrication and functionalization processes. Special focus is placed on the fabrication methods for functionalized materials. In the device section, the review showcases recent breakthroughs in detecting biomacromolecules, cells, solid particles, liquid ions, and gas molecules, offering viewpoints from both biological and chemical angles. Concluding, the paper consolidates current research findings to outline persisting challenges within the realm of optical microcavity-based biochemical sensing and to underscore emerging development trends.

Over the past decade, there have been significant advancements in optical microcavity-based biochemical sensors. These devices, noted for their high-quality factors, compact mode volumes, and robust light-matter interactions, have established themselves as versatile and powerful instruments for measuring and detecting changes caused by external substances. Thanks to the abundance of biochemical sensing principles, along with progress in materials and micro/nano fabrication techniques, optical microcavities can be tailored to specific biochemical environments, unlocking substantial potential for a wide range of applications. These advancements have led to remarkable progress and groundbreaking achievements in key performance metrics such as sensing sensitivity, detection limit, response time, and multi-component selectivity. However, the separation between principles, structures, and device applications presents a barrier that limits the possible synergy between the sensitive enhancements offered by principles and the exceptional properties introduced by structural innovations. This review highlights potential research directions, challenges, and opportunities for the next generation of microcavity-based biosensor devices, aiming to spark further investigation in this area. Key areas for future exploration include: 1. Active Microcavities; 2. Modulation of Interfacial Modes and Amplification Engineering of Interfacial Binding; 3. Label-free Molecular Fingerprinting Development; 4. Integration of Multi-cavity Systems, Cascading, and Arrays; 5. Functionalization and Optimization of On-chip Microcavities; 6. Expanding Sensing Applications Across a Broader Spectrum Range; 7. Investigating Molecular Dynamics and Cellular Evolution; 8. Developing Stable, Miniaturized, and Mass-producible Microcavities.