Effective Synergistic Effect of Dipeptide-Polyoxometalate-Graphene Oxide Ternary Hybrid Materials on Peroxidase-like Mimics with Enhanced Performance

Dipeptide-polyoxometalates (POMs)-graphene oxide (GO) ternary hybrid is an excellent peroxidase-like mimic, exhibiting enhanced peroxidase-like activity compared to POMs alone. The hybrid was readily prepared through a reprecipitation method involving electrostatic encapsulation of H₃PW₁₂O₄₀ (PW₁₂) by cationic diphenylalanine (FF) peptide and coassembly of FF@PW₁₂ spheres with graphene oxide (GO). Using 3,3′,5,5′-tetramethylbenzidine (TMB) as the chromogenic substrate, the peroxidase-like activity of FF@PW₁₂ was evaluated in the heterogeneous phase, and it is 13 times higher than that of pristine PW₁₂ in the homogeneous phase. Furthermore, ternary hybrids of FF@PW₁₂@GO containing 5 wt % GO could enhance the activity 1.7 times higher than that of FF@PW₁₂. The noncovalent interactions of hydrogen bonding and ionic interaction between GO and POMs are speculated to result in the synergistic effect for the enhancement of peroxidase-like performance. The strong interactions between rGO and PW₁₂ are evaluated by a four-probe Hall measurement via the van der Pauw method, and rGO is significantly p-doped by the doping effect of PW₁₂ with lower LUMO energy than that of the energy level of rGO and also due to the electron reservoir feature of PW₁₂. Cyclic voltammogram measurements also suggest that GO causes significant influence on the electronic structure of the reduced forms of the redox couples of PW₁₂. The nature of the TMB catalytic reaction may originate from the generation of the hydroxyl radical (^•OH) from the decomposition of H₂O₂ by ternary hybrids and the formation of peroxo species of POM. Taking advantage of the UV–vis signals of TMB being correlated to the concentration of H₂O₂, FF@PW₁₂@GO can be used to detect H₂O₂ within the limit of detection of 0.11 μM, and the detection range is 1–75 μM. The present method indeed opens up a promising route in constructing heterogeneous peroxidase-like mimics through the use of POMs via the introduction of GO for building H₂O₂ sensors