Abstract
Non-enzymatic biosensors based on mixed transition metal oxides are deemed as the most promising devices due to their high sensitivity, selectivity, wide concentration range, low detection limits, and excellent recyclability. Spinel NiCo(2)O(4) mixed oxides have drawn considerable attention recently due to their outstanding advantages including large specific surface area, high permeability, short electron, and ion diffusion pathways. Because of the rapid development of non-enzyme biosensors, the current state of methods for synthesis of pure and composite/hybrid NiCo(2)O(4) materials and their subsequent electrochemical biosensing applications are systematically and comprehensively reviewed herein. Comparative analysis reveals better electrochemical sensing of bioanalytes by one-dimensional and two-dimensional NiCo(2)O(4) nano-/microstructures than other morphologies. Better biosensing efficiency of NiCo(2)O(4) as compared to corresponding individual metal oxides, viz. NiO and Co(3)O(4), is attributed to the close intrinsic-state redox couples of Ni(3+)/Ni(2+) (0.58 V/0.49 V) and Co(3+)/Co(2+) (0.53 V/0.51 V). Biosensing performance of NiCo(2)O(4) is also significantly improved by making the composites of NiCo(2)O(4) with conducting carbonaceous materials like graphene, reduced graphene oxide, carbon nanotubes (single and multi-walled), carbon nanofibers; conducting polymers like polypyrrole (PPy), polyaniline (PANI); metal oxides NiO, Co(3)O(4), SnO(2), MnO(2); and metals like Au, Pd, etc. Various factors affecting the morphologies and biosensing parameters of the nano-/micro-structured NiCo(2)O(4) are also highlighted. Finally, some drawbacks and future perspectives related to this promising field are outlined.