Direct electrochemistry and electrocatalysis of hemoglobin immobilized into halloysite nanotubes/room temperature ionic liquid composite film

Abstract The novel halloysite nanotubes/room temperature ionic liquid (1-butyl-3-methylimi-dazolium tetrafluoroborate ([BMIM]BF 4 ) composite films were firstly used as an immobilization matrix to entrap hemoglobin (Hb) and its bioelectrochemical properties were studied. FTIR and UV–vis spectroscopy demonstrated that Hb in the HNTs/ILs composite films could retain its native structure. Cyclic voltammetric results showed that a pair of well-defined and quasi-reversible redox peaks appeared in pH 7.0 phosphate buffer solution at the Hb/HNTs/ILs-modified electrode. It indicates the characteristic of Hb heme Fe(III)/Fe(II) redox couple with fast heterogeneous electron transfer rate, which were mostly attributed to the synergistic effect of HNTs and ILs in the composite film and promoting the direct electron transfer between the protein and the underlying electrode. The immobilized Hb showed good electrocatalytic activity to H 2 O 2 with a linear range from 7.5 × 10 −6 to 9.75 × 10 −5  M, and the detection limit was 2.4 μM. The sensitivity and apparent Michaelis–Menten constant were 10.51 μA mM −1 and 369 μM, respectively, which indicated that Hb had a high affinity to H 2 O 2 . It is expected that this composite film may find more potential applications in biosensors and biocatalysis.