The Ritter lab has developed a new method for direct labeling of polypeptides with the [18F]fluoride radiolabel. This Fmoc-protected ruthenium tyrosine is first incorporated into peptides, which is amenable to standard solid-phase peptide synthesis (SPPS) and is tolerant of all 20 canonical amino acids. Subsequent replacement of a single hydrogen with fluorine-18, with only minimal perturbation of the peptide structure, results in a site-specific, radiolabeled peptide tracer for use with positron emission tomography (PET) imaging in the study of various biological applications.