Efficient fluorescence detection of protoporphyrin IX in metastatic lymph nodes of murine colorectal cancer stained with indigo carmine.

•The diagnostic usefulness of protoporphyrin IX (PpIX) fluorescence was evaluated in the presence of indigo carmine by using a mouse model.•Indigo carmine is a blue dye commonly used for identification of sentinel LNs during surgery.•The absorption spectrum of indigo carmine widely overlapped with the fluorescence spectrum of PpIX at the peak of 632nm, but not at the other peak of 700nm.•Fluorescence measurement was more efficient at 700nm than at 632nm for detection of PpIX in metastatic LNs stained with indigo carmine.