Design of a multi-analyte resonant photonic platform for label-free biosensing.

We have designed a multi-analyte biosensing platform based on a hybrid whispering gallery mode resonator to detect protein biomarkers, e.g. those allowing the early diagnosis of Alzheimer's disease. Our proposed biosensor dependent on the hybrid mode naturally extends the capabilities of both plasmonic sensor and photonic sensor and thus performs better interrogation sensitivity. A multi-resonance of the hybrid mode could occur and the field intensity achieved its maximum value, thereby enabling a very strong light-matter interaction. The detection limit for bulk sensing reached a value of 2 × 10-5 RIU and that for surface sensing was at 0.6 pg mm-2. Our novel configuration has an advantage over the conventional plasmonic-waveguide resonator with a similar cavity size (Q-factor < 500) because a wide range of spectral measurements (56 nm) and a high Q-factor (1300) could be achieved simultaneously. Thus, large refractive index shifts in the medium could be detected with high sensitivity. This biosensor, with a footprint of 625 μm2 for each resonator, is a good candidate for integration into lab-on-chip microsystems for large-scale screening of a wide range of protein biomarkers in high risk of developing disease.