EGF and breast carcinoma: Phosphorylation of Y221 in the Picchu-X sensor was triggered by EGFR activation following EGF stimulation (Figures 1a and c); the associated increase in FRET efficiency of the biosensor in transfected HCC1954 breast cancer cells is shown in Figure 1d (shift to ‘warmer’ colours in pseudocoloured micrographs) and Figure 1e.