Plasmonic nanostructures have received increasing attention for photochemical applications due to high light absorptivity, tunability, sensitivity, and robustness. However, the short lifetime of hot electrons limits their efficient extraction, requiring the well-defined assembly of neighboring functional materials (e.g., electron filters and catalysts) along with the plasmonic nanostructures. Here we report the polyphenol-mediated assembly of gold nanoparticles (AuNPs) and titanium dioxide nanoparticles (TiO2 NPs) into colloidal plasmonic heterostructures. Tannic acid (TA) is deposited on the surface of TiO2 NPs through metal-ligand coordination, where TA serves as a reducing agent to synthesize AuNPs on the surface of TiO2 NPs. The generation and injection of hot carriers from the plasmonic heterostructures exhibit faster electron transfer kinetics under visible light illumination as determined using ferricyanide as a redox agent. Subsequent surface coatings of TiO2 NPs with phosphate-functionalized polyethylene glycol is shown as an effective means of selective surface passivation to suppress the charge transfer in the semiconductor/electrolyte interface. We expect that the interface control of plasmonic heterostructures for functional assembly and passivation can be utilized for their photochemical applications through integration with catalytic and sensing components.