Amperometric biosensors based on carbon paste electrodes modified with nanostructured mixed-valence manganese oxides...

Nanostructured, multivalent, manganese-oxide octahedral molecular sieves (OMS), including cryptomelane-type manganese oxides and todorokite-type manganese oxides, were synthesized and evaluated for chemical sensing and biosensing at low operating potential. Both cryptomelane-type manganese oxides and todorokite-type manganese oxides are nanofibrous crystals with subnanometer open tunnels that provide a unique property for sensing applications. The electrochemical and electrocatalytic performance of OMS for the oxidation of H2O2 have been compared. Both cryptomelane-type manganese oxides and todorokite-type manganese oxides can be used to fabricate sensitive H2O2 sensors. With glucose oxidase (GOx) as an enzyme model, amperometric glucose biosensors are constructed by bulk modification of carbon paste electrodes with GOx as a biocomponent and nanostructured OMS as a mediator. A Nafion thin film was applied as an immobilization/encapsulation and protective layer. The biosensors were evaluated as an amperometric glucose detector at phosphate buffer solution with a pH 7.4 at an operating potential of 0.3 V (vs Ag/AgCl). The biosensor is characterized by a well-reproducible amperometric response, linear signal-to-glucose concentration range up to 3.5 mmol/L and 1.75 mmol/L, and detection limits (S/N = 3) of 0.1 mmol/L and 0.05 mmol/L for todorokite-type manganese oxide and cryptomelane-type manganese oxide-modified electrodes, respectively. The biosensors based on OMS exhibit considerable good reproducibility and stability, and the construction and renewal are simple and inexpensive.