D-Ala-Lys-AMCA TFA is a known proton-coupled oligopeptide transporter 1 ( PEPT1 ) substrate that emits blue fluorescence. D-Ala-Lys-AMCA TFA may be transported into liver cancer cells and Caco-2 cells based on fluorescence analysis. D-Ala-Lys-AMCA TFA can be used for characterizing PEPT1-specific substrates or inhibitors.