Silicon nanowire based angle robust ultrasensitive hyperbolic metamaterial biosensor.

We design an angle-robust hyperbolic metamaterial-based biosensor structure using n-doped silicon nanowires. We examine the hyperbolic properties of the structure using effective medium theory (EMT) and analyze the resonance shift of our proposed biosensor structure, by employing the finite-difference time domain (FDTD) method, and theoretically verify the result with the transfer matrix method (TMM). Our proposed sensor structure exhibited a perfect reflectance shift for impedance matching and extreme anisotropic properties at the NIR wavelength (λ > 2.2 μm). We analytically demonstrate the electric field confinement between nanowires by employing the resonance condition, which is enhanced by the total internal reflection (TIR) phase shift. We demonstrate that the angle-insensitive characteristic is inherited by the extreme anisotropic hyperbolic dispersion relation and analyze the effect of structural parameters on the bulk sensitivity using the dispersion relation to optimize the sensor parameters. We explore the sensor performance for detecting the dengue virus and demonstrate that our proposed sensor can detect a single dengue NS1 protein with an outstanding sensitivity of a resonant wavelength shift of 14 nm per NS1 protein and mass sensitivity of 0.192 nm kDa-1. We analyze the ideal limit of detection (LOD) of the NS1 protein solution from the diffusion equation and elucidate that the geometry of the n-Si NW exhibits an unprecedented LOD of 0.691 pM. Our proposed biosensor can be effectively employed for the ultra-sensitive, highly precise label-free detection of various viruses and bacteria at the nanoscale limit.