Dual Responsive Enzyme Mimicking of Ternary Polyaniline–MnO2–Pd Nanowires and Its Application in Colorimetric Biosensing

In recent years, a significant challenge in material science has been to fabricate novel functional nanomaterials to mimic the function of natural enzymatic systems. Herein, ternary polyaniline (PANi)–MnO2–Pd nanowires (NWs) are synthesized through a two-step redox reaction process. The prepared PANi–MnO2–Pd NWs were explored to exhibit dual responsive enzyme-like efficiencies, e.g., peroxidase and oxidase-like activities. With the assistance of H2O2, the obtained ternary PANi–MnO2–Pd NWs were able to oxidize the typical peroxidase substrate of 3,3′,5,5′-tetramethylbenzidine (TMB) to yield the oxidized TMB with a blue color, exhibiting a much better peroxidase-like activity than the synthesized PANi–MnO2 NWs alone and Pd nanoparticles owing to the interfacial electron transfer effect among the components. In addition, in the absence of H2O2, the prepared PANi–MnO2–Pd NWs could also oxidize TMB to display an excellent oxidase-like activity. Based on the dual responsive enzyme-like characteristic of the obtained ternary PANi–MnO2–Pd NWs, a rapid and applicative colorimetric way to sensitively determine l-cysteine and ascorbic acid (AA) has been developed. The limits of detection based on the two systems were estimated to be as low as 118 and 34 nM, respectively. We believe that the prepared ternary PANi–MnO2–Pd NWs with both peroxidase and oxidase-like activities will show broad potential applications in bioscience and bioengineering.