A bio-sensor includes a substrate having a light-sensing region thereon. A first dielectric layer, a diffusion barrier layer, and a second dielectric layer are disposed on the substrate. A trenched recess structure is formed in the second dielectric layer, which is filled with a light filter layer that is capped with a cap layer. A first passivation layer and a nanocavity construction layer are disposed on the cap layer. A nanocavity is formed in the nanocavity construction layer. The sidewall and bottom surface of the nanocavity is lined with a second passivation layer.