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We demonstrate real-time tunability of a chip-based liquid light source enabled by microfluidic mixing. The mixer and light source are fabricated in SU-8 which is suitable for integration in SU-8-based laboratory-on-a-chip microsystems. The tunability of the light source is achieved by changing the concentration of rhodamine 6G dye inside two integrated vertical resonators, since both the refractive index and the gain profile are influenced by the dye concentration. The effect on the refractive index and the gain profile of rhodamine 6G in ethanol is investigated and the continuous tuning of the laser output wavelength is demonstrated using an ethanolic rhodamine 6G solution of 2×10-2 mol/l mixed with pure ethanol. This yields rhodamine 6G concentrations from 5×10-3 to 1.5×10-2 mol/l inside the laser resonators and a wavelength change of 10 nm with a response time of 110 s. [ABSTRACT FROM AUTHOR]