Fig. 4: Demonstration of biosensing by LPM lasers.

a Schematic illustration of specific biomolecule binding at the droplet interface (left panel) and peak wavelength dynamics of the LPM laser (right panel) during biomolecular detection process. SM hopping occurs twice during increasing the analyte concentration, indicating dynamic reconfiguration of the Vernier overlap. b Intensity response of the LPM laser modes with increasing the analyte concentrations (conc.). SM hopping occurs at concentrations of 4.52 pM (SM-1 to SM-2) and 30.1 nM (SM-2 to SM-3). The right inset shows two-dimensional color map of the laser mode intensities under different analyte concentrations. All mode intensities at each concentration are normalized by the intensity sum of the three mode intensities. c Wavelength shifts of the single antibody-functionalized droplets after incubation with different antigens, showing excellent specificity to the target analyte. Error bars are standard deviation (SD) from seven independent experiments. The insets show the fluorescence images of the droplets (see more details in Supplementary Fig. S11). Scale bar, 20 μm. d Spectral response curve for biomolecular binding. Shown are experimental (circles) and simulated (curve) results of the wavelength shift of the single antibody-functionalized droplet versus the antigen concentration. Error bars are SD from three independent experiments.