We demonstrate a new type of photonic crystal nanolaser incorporated into a microfluidic chip, which is fabricated by multilayer soft lithography. Experimentally, room-temperature continuous-wave lasing operation was achieved by integrating a photonic crystal nanocavity with a microfluidic unit, in which the flow medium both enhances the rate of heat removal and modulates the refractive index contrast. Furthermore, using the proposed system, dynamic modulation of the resonance wavelength and far-field radiation pattern can be achieved by introducing a bottom reflector across which various fluids with different refractive indices are forced to flow. In particular, by maintaining a gap between the reflector and the cavity equal to the emission wavelength, highly efficient unidirectional emission can be obtained. The proposed nanolasers are ideal platforms for high-fidelity biological and chemical detection tools in micro-total-analytical or lab-on-a-chip systems. (C) 2008 Optical Society of America.