A new fluorescent biarsenical peptide labeling probe was synthesized and labeled with the radioactive isotopes 11C and 18F. The utility of this probe was demonstrated by installing each of these isotopes into a melanocortin 1 receptor (MC1R) binding peptide, which targets melanoma tumors. Its applicability was further showcased by subsequent in vitro imaging in cells as well as in vivo imaging in melanoma xenograft mice by fluorescence and positron emission tomography.