Fig. 3. Modification of Herceptin™ Fab with reagent 4 and subsequent “click” test reaction. Reagents and conditions: (i) Reagent 4, TCEP·HCl, borate buffer pH 8.0 (5 mM EDTA), 21 °C, 16 h; (ii) Alexafluor®-488-N₃, phosphate buffer (pH 7.4), 21 °C, 2 h.