QE and bivQ probe showing specific accumulation in vital regions of A431/CCK2R, but not of A431/WT tumours. (a) Ex vivo fluorescence images of tumour slices of animals that were injected with QE, bivQ and DY-754. The last column shows the native tumours. Images were obtained with an Odyssey slide scanner at 700 nm (autofluorescence) and 800 nm (probe fluorescence). All images are comparable in terms of their fluorescence intensity (white, lowest FI; black, highest FI). Representative images of three specimens/group are displayed. (b) Immunohistochemical staining of CCK2R in A431/CCK2R and A431/WT tumours. Red, CCK2R staining (see ‘Methods’); blue, cell nuclei staining with Mayer's haematoxylin.