CFP and pemphigus foliaceus: The results presented that the fluorescence of CFP with pseudo‐green color and YFP with pseudo‐red color, and merged pseudo‐yellow color, were both activated in lung tissues of PF mice, which clarified that overexpressed caspase‐3 in injured AECs II could break amino acid bonding (‐DEVD‐) to restrain energy transfer from CFP chromophores to YFP chromophores, showing a state of diagnostic “ON” based on FRET principle in PF mice (Figure 6B).