TfR-T12 is a BBB-penetrated transferrin receptor (TfR) binding peptide, displaying a binding affinity in the nM range.The 12-mer peptide sequence is a transferrin receptor (TfR) targeting peptide. It binds to TfR and is internalized via endocytosis into TfR-expressing cells. TfR targeting peptide is a potential carrier for transportation of small molecules across the blood-brain barrier to the brain, or into malignant tissues.