Ultra-sensitive bio-sensor based on GMR in self-suspended-membrane-type germanium grating

In this paper, an ultra-sensitive bio-sensor based on the GMR effect in self-suspended-membrane-type gratings (SSGs) is proposed using multilayer plane waveguide theory. It is demonstrated from our calculations that the sensitivity of our bio-sensor is near the theoretical limit compared with a conventional GMR sensor. Based on the normalized eigenfunction of a single-layer homogeneous grating, the resonance curves with respect to different refractive indices of surrounding media are calculated, which confirm the estimated sensitivity. In addition, we design a highly sensitive bio-sensor in the near- and mid-IR wavelength region for liquid and gas detection respectively, the sensor can deliver a resolution over 1 x 10(-5) in the near-IR region in a large refractive index (1.3-1.7) range and provide better than 1 x 10(-6) in the mid-IR region, which is enough for various bio-material detections. Therefore, the bio-sensor we proposed is one or two orders more sensitive than conventional GMR sensors.