With a Caspase-3 activatable photoacoustic imaging probe, the drug-induced  tumor apoptosis could be detected and located within a whole tumor in a living mouse. Imagine like "Wu Kong's fire eyes". More story about this in the paper entitled "A Photoacoustic Probe for the Imaging of Tumor Apoptosis by Caspase-Mediated Macrocyclization and Self-Assembly" that was done by Yuqi Wang and published in Angew. Chem. Int. Ed. this year.