Multicomponent nanohybrids of nickel/ferric oxides and nickel cobaltate spinel derived from the MOF-on-MOF nanostructure as efficient scaffolds for sensitively determining insulin.

Multicomponent nanohybrids of nickel/ferric oxides and nickel cobaltate spinel (denoted as NiO/FeO/NiCoO) have been prepared through pyrolyzing the hierarchical nanostructure of MOF-on-MOF and explored as efficient scaffolds for sensitively determining insulin. As for the MOF-on-MOF preparation, the ultra-thin bimetallic CoNi-zeolitic imidazolate framework (CoNi-ZIF) nanosheets were grown tightly around the bimetallic CoFe Prussian blue analogue (CoFe PBA) nanocube (denoted as CoNi-ZIF@CoFePBA). Basic characterizations revealed the original core-shell structure shape was still maintained in the NiO/FeO/NiCoO pyrolyzed at 300 °C, which was composed of multi-metal oxides and NiCoO spinel, along with low crystallinity. Conversely, the NiO/FeO/NiCoO nanohybrid calcined at 600 °C consisted of large amounts of nanoparticles, while the nanohyrbid obtained at 900 °C demonstrated aggregated NiO and FeO nanoparticles coexisted with the NiCoO phase. Owing to the porous nanostructure, the synergistic effect among different components, excellently electrochemical conductivity, and good biocompatibility of the NiO/FeO/NiCoO nanohybrid obtained at 600 °C, the relevant aptasensor displayed superior sensing performance for the determination of insulin. It gave an ultra-low detection limit of 9.1 fg mL (0.16 fM) within a wide linear insulin concentration ranging from 0.01 pg mL (0.172 fM) to 100 ng mL (1.72 nM) determined by the electrochemical technique. The constructed aptasensor also had high selectivity, good stability, excellent reproducibility, and acceptable applicability in human serum. By integrating the advantages of aptasensors and electrochemical approach with features of multi-metallic metal-organic frameworks, this work widely broadens the applications of MOF-driven nanohybrids in biosensing fields.