Silicon photonic crystal nanocavity-coupled waveguides for error-corrected optical biosensing

A photonic crystal (PhC) waveguide based optical biosensor capable of label-free and error-corrected sensing was investigated in this study. The detection principle of the biosensor involved shifts in the resonant mode wavelength of nanocavities coupled to the silicon PhC waveguide due to changes in ambient refractive index. The optical characteristics of the nanocavity structure were predicted by FDTD theoretical methods. The device was fabricated using standard nanolithography and reactive-ion-etching techniques. Experimental results showed that the structure had a refractive index sensitivity of 10−2 RIU. The biosensing capability of the nanocavity sensor was tested by detecting human IgG molecules. The device sensitivity was found to be 2.3 ± 0.24 × 105 nm/M with an achievable lowest detection limit of 1.5 fg for human IgG molecules. Additionally, experimental results demonstrated that the PhC devices were specific in IgG detection and provided concentration-dependent responses consistent with Langmuir behavior. The PhC devices manifest outstanding potential as microscale label-free error-correcting sensors, and may have future utility as ultrasensitive multiplex devices.