Material-Selective Polydopamine Coating in Dimethyl Sulfoxide

Polydopamine coating is known to be performed in a material-independent manner and has become a popular tool when designing a surface-functionalization strategy of a given material. Studies to improve polydopamine coatings have been reported, aiming to reduce the coating time (by transition metals, oxidants, applied voltages, or microwave irradiation), control surface roughness using catechol derivatives, and vary the ad-layer molecules formed on an underlying polydopamine layer. However, none of the techniques have changed the most important intrinsic property of polydopamine, the surface-independent coating. Currently, no method has been reported to modify this property to create a material-selective 'smart' polydopamine coating. Herein, we report a method with polydopamine to differentiate the chemistry of surfaces. We found that the polydopamine coating was largely inhibited on silicon-containing surfaces such as Si wafers and quartz crystals in a dimethyl sulfoxide (DMSO)/phosphate-buffered saline (PBS) cosolvent, while the coating properties on other materials remained mostly unchanged. Among the various interface bonding mechanisms of coordination, namely, cation-π, π-π stacking, and hydrogen-bonding interactions, the DMSO/PBS cosolvent effectively inhibits hydrogen-bond formation between catechol and SiO₂, resulting in surface-selective 'smart' polydopamine coatings. The new polydopamine coating is useful for functionalizing patterned surfaces such as Au patterns on SiO₂ substrates. Considering that Si wafer is the most widely used substrate, the surface-selective polydopamine coating technique described herein opens up a new direction in surface functionalization and interface chemistry.