Engineering Design of an Expandable 1-D Photonic Crystal Slab Biosensor Array for Joint Detection of Multiple Tumor Markers

This article proposed a silicon-on-insulator (SOI)-based optofluidic 1-D photonic crystal slab biosensor array structure for multiple tumor markers detection. The array consists of multiple expandable sensing branches, each composed of a nanobeam resonator transducer with excellent detection limit, a filter with low sidelobe jitter, and a microfluidics roof. Using the 3-D finite-difference time-domain (FDTD) method, a 1-D photonic crystal slot nanobeam resonator transducer consisting of a circular hole array linearly decreasing from the center to both ends was obtained. Under the influence of absorption loss of biological solution, the transducer works in the communication E-band, with the Q-value up to 10487, refractive index sensitivity of 355 nm/RIU, and refractive index detection limit of $2.61\times 10^{-{5}}$ RIU, corresponding to the detection of fg/mL carcinoembryonic antigen, which can be directly used for the detection of tumor marker under the capture of antibody probes in microfluidics chip. By optimizing the apertures on both sides of 1-D photonic crystals with a tapered shape, a cutoff filter with low sidelobe jitter can effectively filter out the high-order resonant peaks of the transducer, forming a large free spectral range (FSR). More importantly, the aforementioned sensing branch can be extended into arrays based on the frequency band effect of photonic crystals. This article provided the expansion method and examples to verify that the extended branches have equally excellent detection performance and analyzed the reasons why the sensing array has high MEMS preparation robustness. The array structure provides a good choice for label-free point-of-care detection of multiple tumor markers.