Biotin labeling

Biotin can be attached to the peptide N-terminus or the C-terminus (via lysine or cysteine). Due to the very strong
non‐covalent interaction between biotin and avidin / streptavidin, it is useful to have this small molecule as a tag
to immobilise the peptide, or to pull‐ down the peptide from a mixture. Note that a spacer, such as a mini-PEG
or Ahx (aminohexanoic acid), between biotin and the N‐terminus give a better performance in biotechnological
applications generally.

                                                                                                                                                                                               
Tagged peptides 

Peptide tags are widely used in protein expression and purification, and also be used to protein detection through
Western blot, ELISA, ChIP, immunocytochemistry, immunohistochemistry, and fluorescence measurement.
 

Cell-penetrating peptides

Cell-penetrating peptides has been developed as an in vitro and in vivo delivery vectors to be used to facilitate localization to specific cellular compartments (membranes, cytoplasm).