Some embodiments of the present disclosure provide an optical sensor. The optical sensor includes a semiconductive substrate; a light sensing region on the semiconductive substrate; a waveguide region configured to guide light from a wave insert portion through a waveguide portion and to a sample holding portion; and an interconnect region below the waveguide region, and the interconnect region being disposed above the light sensing region. The waveguide portion includes a first dielectric layer comprising a first refractive index and at least one second dielectric layer comprising a second refractive index, wherein the second refractive index is smaller than the first refractive index.