Enhanced Biomolecule Concentration Sensing by Using Exceptional Points in a Microtube Cavity With Multiple Layers

Biosensors have important implications for medical research and disease prevention. High-quality optical microcavities with whispering-gallery modes (WGMs) can enhance light-matter interactions in small volumes, making them ideal for making biosensors. However, the sensitivity of the optical microcavity biosensors can further improve. The sensing performance of the biosensor based on a microtube or microbubble can be further improved by exceptional points (EPs) in non-Hermitian physics. Non-Hermitian systems are open systems, exchanging energy with the external environment. EPs as one representative feature of non-Hermitian systems are a branch point singularity, where eigenvalues and their corresponding eigenvectors coalesce in the parameter space of the system. In the vicinity of EPs, the eigenvalues exhibit non-trivial topology, which can be exploited for highly sensitive detections. Based on this principle, a novel configuration with multiple layers is proposed, where the coupling of modes can be tailored for EPs by choosing the thickness of layers. Simulated results demonstrated that the design has strong biosensing performance. The sensitivity can be enhanced by 1000 times more than that of conventional methods. The ability to prevent environmental interference has also been improved. This is significant for highly sensitive low-concentration biomolecule detection in microtubes in the future.