|Other Abstract||Electrochemical glucose biosensor plays important roles in both diabete diagnostics and industrial bioprocess monitoring. As the foundation of the electrochemical sensor, the electrode materials or the recognition elements are improved by intruducing a variety of nanomaterials. Among the various nanomaterials, transition metal oxides have been widely applied on the electrochemical glucose sensor, due to their unique physicochemical properties. However, the conventional synthesis methods generally require complex process, expensive equipments and precursors, skilled workers, high consumption of energy, unsafe condition or harmful reagents. In addition, the nanomaterials from these methods lack complicated structure and morphology, and their electrochemical performances still need to be improved. To overcome these challenges, our aim is to prepare the novel nanomaterials with high electrochemical sensing performance by the green, simple, facile and cost-effective bio-templated strategy.
As a kind of attractive transition metal oxide, manganese dioxide (MnO2) with different morphologies, has been widely studied on the field of electrochemistry and analytical chemistry, due to its electrocatalytic activity, chemical catalysis, environmental friendliness and nontoxicity. Among the different morphologies of MnO2, one-dimensional (1D) nano-structured morphologies have attracted more and more interests for electrochemical applications (such as supercapacitor, ion battery and electrochemical sensor), due to the controlled structure for electron transfer, quantum size effect and surface effect. To conveniently obtain 1D MnO2 nanowires (NWs) with controlled structure and unique properties under mild conditions, the genetically engineered M13 phages were useed as templates for precise nucleation and growth of MnO2 crystals on filamentous phage scaffolds, via the spontaneous oxidation of Mn2+ in alkaline solution. It was found that the morphology of NWs could be tailored by the surface charge of M13 mutants. MnO2 crystals were uniformly distributed on the surface of negatively-charged tetraglutamate-fused phage (M13-E4), significantly different from irregular MnO2 agglomeration on the weakly negatively-charged wild-type phage and positively-charged tetraarginine-fused phage. The as-synthesized M13-E4@MnO2 NWs could catalyze the electro-oxidation of H2O2 at neutral pH. To demonstrate the superiority of the electrocatalytic activity in the solution containing plenty of chloride ions at neutral pH, both glucose oxidase and as-prepared MnO2 NWs were used for fabricating the glucose biosensor. The proposed biosensor showed a wide linear range (0.005~2 mM glucose), rapid response (within 5 s), an acceptable limit of detection (1.8 μM glucose, S/N = 3), good inter-and intra-assay reproducibility, satisfactory storage stability and reliability of real sample detection. Due to the superiorities on synthesis and electrochemical performance, the MnO2 NWs are promising to be applied on electrocatalysis, electrochemical sensor, and supercapacitor.
Although the above biosensor exhibits improved performance, there were still some disadvantages: low stability (mainly ascribed to enzymes) and low sensitivity. Therefore, we chose cobalt oxide (Co3O4), a kind of electrocatalyst of glucose oxidation, to fabricate the electrochemical non-enzymatic sensor. To obtain the direct electrochemical sensing interface with large surface area, a novel three-dimensional (3D) porous Co3O4 architecture was first synthesized through a simple, cost-effective and environmentally friendly leaf-templated strategy. The Co3O4 nanoparticles (30~100 nm) were interconnected with each other to form a 3D porous structure, which provided high specific surface area and numerous electrocatalytic active sites. Subsequently, Co3O4 was successfully utilized as direct electrochemical sensing interface for non-enzymatic detection of H2O2 and glucose. The fabricated Nafion/Co3O4/GCE glucose sensor showed not only the rapid response, high sensitivity (439.39 μA mM-1 cm-2) and low detection limit (0.1 μM glucose, S/N = 3), but also excellent stability, anti-interference performance for possible interferents (such as ascorbic acid, uric acid, dopamine, acetaminophen and especially 0.15 M chloride ions) and reliability for blood glucose detection. In conclusion, due to the superiorities on synthesis and performance, 3D porous Co3O4 is promising for possible applications in electrocatalysis, electrochemical sensor and supercapacitor. In addition, the proposed synthesis strategy may be applicable to prepare a wide range of metal or metal oxide nanostructures. Considering the different nanostructures and properties from different synthesis condition and metal oxides, various potential applications are envisioned.|