PTAD linkers are bioconjugation linkers designed for selective modification of tyrosine residues in proteins and peptides. Featuring a PTAD (4-phenyl-3H-1,2,4-triazoline-3,5(4H)-dione) group, they react specifically with tyrosine while minimizing cross-reactivity with other amino acids. Often equipped with azide or alkyne groups, PTAD linkers enable bioorthogonal click chemistry, such as CuAAC, for attaching drugs, imaging agents, or probes. Variants with PEG spacers enhance solubility and flexibility, and some include cleavable motifs for controlled payload release in antibody-drug conjugates. PTAD-tyrosine bonds are stable across diverse pH and temperature conditions, making these linkers versatile for targeted drug delivery, protein labeling, and biosensor development.