Fig. 1

a The formation diagram and scanning electron microscope (SEM) image of dual-emission fluorescent silica nanoparticles with reference dye (TRITC) and sensor dye (FITC); the confocal fluorescence microscopy image of RBL mast cells (red as TRITC silica particles and green as AlexaFluor 488-Cholera toxin B); confocal fluorescence microscopy images of RBL mast cells as pH sensors. b For reference channel, c for sensor channel, d for the overlaid images, and e false-color ratiometric imaging for pH values calculated according to the experiments [22]