Scheme. 1

Schematic illustration of HFI for real-time monitoring viscosity and pH fluctuations in lysosomes during autophagy. Compared with other organelles, only lysosomes with highly viscous and acidic microenvironments could be specifically lit by probe HFI. Once facing nutrient-deprivation or external stress, the ratiometric fluorescent signal (R = I ₆₁₀/I ₄₆₀) of HFI would raise with time to reveal the autophagic details