Wideband Tuning and Deep‐Tissue Spectral Detection of Indium Phosphide Nano‐Laser Particles

Laser particles (LPs) emitting narrowband spectra across wide spectral ranges are highly promising for high-multiplex optical barcoding of biological cells. Here, LPs based on indium phosphide (InP) nanodisks are presented, operating in the near-infrared wavelength range of 740-970 nm. Utilizing low-order whispering gallery resonance modes in size-tuned nanodisks, an ultrawide color palette with 25% spectral utilization and nanometer-scale linewidth is achieved. A simple theoretical model accurately predicts spectral ranges based on particle size. The minimum laser size is 430 nm in air and 560 nm within cells, operating at mode orders of 4 or 5. The high brightness and narrow linewidths of polymer-silica-protected InP LPs, combined with a silicon-detector spectrometer, enable spectral detection of laser peaks with high signal-to-background ratios in highly-scattering media, including 1-cm-thick chicken breast tissue and blood vessels in live mice.