Layer-by-layer assembled hybrid film of carbon nanotubes/iron oxide nanocrystals for reagentless electrochemical detection of H2O2

A new approach to construct a reagentless electrochemical H2O2 sensor is described. Iron oxide magnetic nanocystals (IOMNs), as peroxidase mimetics, were assembled to form a multilayer structure through the layer-by-layer (LBL) method. Polythionin (PTh) was first electrodeposited onto the glassy carbon electrode (GCE) surface to introduce amino groups. Carboxyl functionalized multi-walled carbon nanotubes (MWCNTs), amino functionalized IOMNs, and thionin monomers were alternatively anchored onto a polythionin-functionalized GCE surface in order by carbodiimide or glutaraldehyde chemistry. The resulting multilayer construction with three layers of IOMNs and thionin mediator exhibits excellent electrochemical response to the reduction of H2O2, whereas such a modified electrode with one layer construction only yields a slight response to H2O2 of the same concentration. The tethered MWCNTs enlarge the amount of immobilized IOMNs and effectively shuttle electrons between the electrode and the thionin. The calibration plot is linear over the wide H2O2 concentration range from 0.099 to 6.54 mM, with a detection limit of 53.6 μM.