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

ABSTRACT 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.