Measurement scheme, SEM and TEM of a lasing enhanced surface pleamon sensor (a) The schematic of the device and the measurement scheme. Comparing to the SPR sensors, an additional semiconductor layer is added between flat metal surface and analyte as gain material. Under optical pumping, the excited carriers in the semiconductor recombine and radiate dominantly to surface plasmons due to Purcell factor which avoids the sophisticated setup required for the indirect generation of surface plasmons by phase match. (b) A schematic showing that, for a given resonance peak shift, a resonance with narrower linewidth will have larger intensity change. Due to the coherence natural of the lasing emission by amplification of the stimulated emission, the signal from such a LESPR sensor has a much narrow linewidth comparing to the SPR sensor. For a given resonance peak shift, there will be a dramatic intensity change at a certain wavelength. (c) A SEM image of the fabricated device consisting of a CdSe nanosquare atop of Au substrate separated by a few nanometer MgF2. The band edge emission of CdSe is around 700 nm locating in the biosensing preferred region. The Au is chosen because it is much stable comparing to silver. The scale bar is 2 µm. (d-e) High resolution TEM images for of CdSe nanosquare (d) and Au/MgF2 substrates.