Breaking the Bottleneck in Limit of Detection of Surface Refractive Index Sensing by Harnessing Meta‐Waveguide Microring Resonators

Pushing sensor sensitivity to the extreme remains a central pursuit in sensing research. However, the limit of detection (LOD) is ultimately limited by the trade-off between intrinsic sensitivity and noise: improvements in sensitivity often introduce higher noise, yielding only marginal gains in LOD. Here, we leverage mode splitting in meta-waveguide microring resonators (MWMRs)-a typically overlooked phenomenon-to suppress drift-induced bias and noise without sacrificing interfacial refractive-index sensitivity. This approach reduces baseline drift to just 4.6 fm/min during representative measurements, enabling quantitative detection of ultra-weak surface perturbations. The sensing performance is validated through the streptavidin-biotin interaction, achieving reliable detection of 0.01 pg/mL streptavidin with a blank reference and a splitting noise of 1.3 pm. This reflection-induced mode splitting framework breaks the longstanding LOD bottleneck in surface refractometric sensing and establishes MWMRs as a robust, drift-immune platform for ultra-sensitive optical interrogation.