Ultra-compact dual-microcavity sensor for label-free immunoglobulin G detection

Biomarkers, such as immunoglobulin G (IgG), play a critical role in disease diagnosis and related fields. To address spatial constraints in biomarker detection, it is essential to develop an ultra-compact sensor with high sensitivity. In this study, we construct dual microcavities in series using two-photon polymerization (TPP) onto the end face of a fiber. The sensor, with a total height of 86 μm, achieves a refractive index sensitivity of 8256.2 nm/RIU, representing a 7-fold enhancement compared to a single microcavity with identical parameters. Additionally, the sensor demonstrates IgG detection with a limit of detection (LOD) as low as 28.6 ng/mL. By confining the sensor to the microscale while maintaining high sensitivity, this work presents a novel approach for the in vivo detection of IgG and other biomarkers.