Nanoscale radius-graded photonic crystal sensor arrays using interlaced and symmetrical resonant cavities for biosensing

•This paper proposes nanoscale photonic crystal sensor arrays using radius-graded structure for biosensing.•The sensor arrays can detect different molecules at the same time without crosstalk.•The device is novel with four symmetrical nanocavities interlaced-coupled along the W1 waveguide which can largely decrease the sensing footprint.•The radius-graded photonic crystal is more suitable for monolithic integration in actual design and applications.

In this work, we propose radius-graded photonic crystal sensor arrays applied on nano-scale optical platform for label-free biosensing. Two L3 cavities and two H1 cavities are multiplexed and interlaced on both sides of a photonic crystal W1 waveguide on the radius-graded photonic crystal slab. The optical sensing characteristics of the nanocavity structure are predicted by three-dimensional finite difference time domain (3D-FDTD) simulation. In response to the refractive index change of air holes surrounding the cavities, four interlaced and symmetrical cavities are shown to independently shift their resonant wavelength without crosstalk. The simulation results demonstrate the refractive index sensitivity of sensor array varies from 66.67 to 136.67 nm/RIU corresponding to the number of functionalized air holes ranged from 4 to 21. This design makes different cavities multiplexed on both sides of waveguide possible. Meanwhile, the radius-graded photonic crystal with more symmetrical and interlaced cavities is better for large integration in the sensor arrays.