Surface coating with multifunctional properties has been of great interest, owing to their potential in various applications such as anti-corrosion, catalysis or targeted drug delivery system. Various techniques including electrospinning, dip coating or layer-by-layer (LbL) deposition have been widely used. Especially the latter one has shown some advantages over other techniques such as substrate-surface independence, fine tuning of coating layer composition or thickness. However, timeconsuming processes, difficulty to be up-scaled are the main drawback of this method for the practical applications.Very recently, an extremely rapid, one-step coating method consisting in coordination complex of metal ions (e.g., Fe +3 ) with natural polyphenols (e.g., tannic acid) was reported. 1 These metal-phenolic networks (MPNs) can be deposited on the surface of substrate by simple mixing of abovementioned coating components in one-pot without any further treatment ( Figure 1). The formation of MPNs occurs through the following mechanism: metal ions or polyphenolic ligands are firstly adsorbed on the surface of substrate, then the pyrogallol moieties are crosslinked with chelating metal ions. Apart from its simple process, the main advantages of MPN are that (1) the coating can be achieved in less than 1 min, (2) the thickness can be easily controlled by adjusting the concentration of coating components, (3) multiple coating layers with different chemical composition is possible via the LbL approach, and (4) the stability of coating can be modulated by changing metal ions or polyphenols, for example using di-, tri-or tetra coordinating ions (Cu 2+ , Fe 3+ , Ti 4+ ). 2 Like other common metal-ligand complexes, MPNs are highly sensitive to variation of pH, which enable them to be used as promising drug delivery system. MPNs might coat surfaces of porous inorganic (e.g., CaCO 3 , silica) 3,4 or polymeric spherical capsules, 5 where the drug is readily loaded. Lowering pH from 7.4 to 5, promotes MPNs disassembly and thus triggered drug release. More importantly, the disassembly rate at low pH depends on the nature of metal ions. For instance, MPNs with tetra-valent metal ions (e.g., Zr 4+ ) are generally more stable than di-valent metal ions (e.g., Cu 2+ ). MPNs crosslinking Fe 3+ or Al 3+ have 9-12 h half-life time of disassembling at pH 5. Thus, these coating layers are suitable candidates not only for extended drug release vector, but also for target drug delivery in cancer tissues, where the pH value (around 5-6) is lower than in physiological condition (pH 7.4). 3 Asides from pH-responsive feature, metal ions of MPNs can be used for their instinct properties, for example, Gd 3+ in magnetic resonance imaging (MRI) with enhanced nuclear relaxation rates. Mixing with other metal ion (e.g., Cu 2+ and Eu 3+ ) in the framework of MPNs is also possible, providing, in this case, dual responsive characters to positron emission tomography (PET) and fluorescence imaging for X-ray spectroscopy (EDX) mapping analysis. 6 Moreover, most o...