  This work demonstrates the Nd:YAG waveguide laser as an efficient platform
for the bio-sensing. The waveguide was fabricated in the Nd:YAG crystal by the
cooperation of the ultrafast laser writing and ion irradiation. As the laser
oscillation in the Nd:YAG waveguide is ultra-sensitivity to the external
environment of the waveguide. Even a weak disturbance would induce a large
variation of the output power of the laser. According to this feature, the
Nd:YAG waveguide coated with Graphene and WSe2 layers is used as substrate for
the microfluidic channel. When the microflow crosses the Nd:YAG waveguide, the
laser oscillation in the waveguide is disturbed, and induces the fluctuation of
the output laser. Through the analysis of the fluctuation, the concentration of
the dextrose solution and the size of the tumor cell are distinguished
