Latest Collaborative Contribution from Prof. Mohamad Sawan's Research Group：An Analyte-medium Metacavity for High Sensitivity and High Q-factor Sensing.

Micro/Nanophotonic devices manipulate light at subwavelength scales and boost light-matter interactions. Thus, they have presented promising avenues for advanced biosensors.

To date, a variety of photonic sensing platforms have been demonstrated to achieve high sensitivity, large throughput and point-of-care detection. Plasmonic sensors based on metals, such as localized surface plasmon resonance and surface-enhanced Raman scattering, have been widely reported for biosensing applications. However, due to the intrinsic high losses of metallic materials in the optical range, the Q-factor of plasmonic sensors is significantly limited, often in the range of tens to hundreds, leading to a lower sensing figure of merit (FoM).

Therefore, dielectric-based micro/nano resonators have garnered significant attention. The Q-factor of dielectric devices far exceeds that of plasmonic sensors owing to their lower material losses, even reaching up to 10⁶. Regarding sensing applications, high sensitivity and high Q-factor are crucial for achieving outstanding sensing performance in photonic biosensors. However, strongly confined optical field and high interaction intensity between light and biomolecules on the surface of optical sensors are typically difficult to satisfy simultaneously. This inherent "trade-off" effect has become one of the main challenges faced by micro/nano optical biosensors.

In recent research, CenBRAIN Neurotech Center of Excellence proposed adistinctive configuration for addressing this issue: embedding a nanophotonic metasurface inside a micro-vertical cavity and have the analyte solution serves directly as the cavity medium by a customized microfluidic channel. The novel configuration, namely Metacavity, achieved strong optical confinement at the structure-environment interface, thereby maximizing the light–analyte interaction. This work, entitled “High Quality–Factor All–Dielectric Metacavity for Label–free Biosensing”, has been published in Advanced Science.

Figure 1. Illustration of the metacavity biosensor and the simulation optical properties.

Ph.D student Yuqiao Zheng from CenBRAIN Neurotech Center of Excellence and Ph.D student Jiacheng Sun from Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang Province are the first authors of this paper. Dr.Liaoyong Wen, Assistant professor (independent PI), Dr. Sumin Bian, Research Associate Professor and Dr. Mohamad Sawan, Chair Professor from Westlake University are the corresponding authors.

Reference

Zheng Y., Sun J., Ma Y., Zhang H., Cui Z., Paschos G., Song X., Tao Y., Savvidis P., Kong W., Wen L., Bian S., Sawan M. “High Quality–Factor All–Dielectric Metacavity for Label–free Biosensing”, Advanced Science, 2024, 2410125.

More information can be found at the following link:

https://doi.org/10.1002/advs.202410125

Abstract

High sensitivity and high quality-factor are crucial for achieving outstanding sensing performance in photonic biosensors. However, strong optical field confinement and high light–biomolecule interactions on photonic surfaces are usually contradictory and challenging to satisfy simultaneously. Here, we report a distinctive configuration for addressing this issue: embedding a nanophotonic metasurface inside a micro vertical cavity as a meta-channel (metacavity) biosensor. The analyte solution serves as the cavity medium, thereby maximizing the light–analyte interaction. Simulation validation is conducted to optimize the metacavity with high structural robustness and remarkable optical and sensing properties. Large-scale low-cost metacavity biosensors are realized by combining anodic aluminum oxide template technique and wafer bonding. Experimentally, the metacavity biosensor demonstrates a notable quality-factor (maximum 4140) and high bulk refractometric sensitivity (450 nm/RIU), resulting in an unprecedented figure-of-merit (1670 RIU^-1). Moreover, the metacavity biosensor achieves high surface sensitivity, together with a detection-limit of 119 viral copies/mL for label-free SARS-CoV-2 pseudovirus sensing, revealing remarkable performance in both bulk and surface sensing.

Figure 2. Sensing properties of the Metacavity and bare microcavity.

Figure 3. Biosensing properties of the Metacavity and bare microcavity.

Research Highlights

-Embeddingnanoscale metasurface into microscale optical cavity, achieving strong light field confinement at the structure-environment interface.

-Having the analyte directly serve as the cavity medium, empowering strong light-matter interaction.

-Experimentally, metacavity achieves both high Q-factor and high sensitivity, resulting in an unprecedented figure-of-merit.