Fig. 1: Configuration of LPM laser for biosensing.

a Schematic of an LPM laser consisting of two size-mismatched dye-doped droplets immersed in an aqueous environment. A 532 nm pulsed laser is used to excited the optical WGMs of the droplet microresonators (μRs). Adjacent droplets are optically coupled through spatially overlapped evanescent fields. b Numerical simulation of the electric field distribution in the coupled droplet μRs with diameters of 42 (μR₁) and 32 µm (μR₂). The amplitude of the electric field |E| distributed on the x-z plane is plotted for the coupled WGMs, where strong evanescent field overlaps and photon exchange occurs at the gap region. Detailed simulation parameters are given in Methods. c Illustration of the LPM supporting a lower (an order of magnitude (mag.)) threshold single-mode (SM) laser emission (left panel) and an amplified mode shift (right panel) compared to single droplets. Reconfiguration of the Vernier overlap between specific lasing modes of both droplet μRs enables a significant mode hopping with a magnification (mag) factor of ~10. d Schematic concept of the LPM laser as a highly sensitive biosensor. Intensity response of the LPM laser modes serves as sensitive sensing signal output, which is utilized to identify biological binding events at the cavity interface.