We report on fabrication of a microtoroid resonator of a high-quality factor(i. e., Q-factor of ~3.24x10^6 measured under the critical coupling condition)integrated in a microfluidic channel using femtosecond laser three-dimensional(3D) micromachining. Coupling of light into and out of the microresonator hasbeen realized with a fiber taper that is reliably assembled with themicrotoroid. The assembly of the fiber to the microtoroid is achieved bywelding the fiber taper onto the sidewall of the microtoroid using CO_2 laserirradiation. The integrated microresonator maintains a high Q-factor of3.21x10^5 as measured in air, which should still be sufficient for many sensingapplications. We test the functionality of the integrated optofluidic sensor byperforming bulk refractive index sensing of purified water doped with tinyamount of salt. It is shown that a detection limit of ~1.2x10^-4 refractiveindex unit can be achieved. Our result showcases the capability of integrationof high-Q microresonators with complex microfluidic systems using femtosecondlaser 3D micromachining.
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