Nanolasers, which could be used to supply light to lab-on-a-chip devices, have been made with solid lasing, or “gain,” materials. But the output of these light sources couldn’t be tuned after fabrication. Teri W. Odom of Northwestern University and coworkers have now made plasmonic nanolasers that are tunable from 858 to 913 nm in real time (Nat. Commun. 2015, DOI: 10.1038/ncomms7939). The researchers made the nanolasers from a gold nanoparticle array surrounded by a liquid gain material composed of dye molecules dissolved in organic solvent. The nanolaser is activated by pumping it optically with an external light source. The resulting emission wavelength is dictated by the refractive indexes of the solvent and the substrate. Thus, for a given substrate and nanoparticle array, changing the solvent changes the emission wavelength. By integrating the nanoparticle array in a microfluidic device, the researchers were able to change the solvent and the lasing wavelength in real time. For example, a nanolaser made from the dye IR-140 in dimethyl sulfoxide and a nanoparticle array on fused silica emitted light at 862 nm. By switching to benzyl alcohol, the same device lased at 891 nm.