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Figure 4: Metal-free functionalization of peptide and protein. (a) Schematic illustration for the thiol-yne click conjugation of Tat peptide with TPA, affording one cell-penetrating peptide conjugate, Tat-TPA. The sequence of Tat peptide is YGRKKRRQRRR. (b) Fluorescent emission spectrum of Tat-TPA ( = 405 nm, insert photographs: Tat-TPA aqueous dispersion under white light and UV irradiation). (c) CLSM images of EMT-6 cells upon 30 min incubation with the aqueous dispersion of Tat-TPA and TPA at 2 μM. No detectable fluorescence was observed for cells incubated with TPA. (d) Schematic illustration for the click conjugation of BSA with TPA, affording BSA conjugates, BSA-TPA. (e) Hydrodynamic diameter distribution of BSA and BSA-TPA in water (Inset: TEM image determined for BSA-TPA in water). (f) Photographs of BSA-TPA aqueous dispersion under white light and UV irradiation. (g) SDS-PAGE results recorded for BSA and BSA-TPA, and lower row image was taken under UV irradiation.