Direct electrochemistry of immobilized hemoglobin and sensing of bromate at a glassy carbon electrode modified with graphene and β-cyclodextrin

We describe the use of a nanocomposite consisting of graphene and beta-cyclodextrin (beta-CD) which was used to modify a glassy carbon electrode (GCE) to serve as a matrix for immobilization of hemoglobin (Hb). The composite was characterized by scanning electron microscopy, UV-vis and FTIR spectroscopy. The modified electrode displays an enhanced and well-defined quasi reversible peaks for the heme protein at a formal potential of -0.284 V (vs. Ag/AgCl). The direct electrochemistry of Hb is strongly enhanced at this modified electrode compared to electrodes not modified with graphene or beta-CD. The heterogeneous electron transfer rate constant (Ks) is 3.18 +/- 0.7 s(-1) which indicates fast electron transfer. The biosensor exhibits excellent electrocatalytic activity towards the reduction of bromate, with a linear amperometric response in the 0.1 to 176.6 mu M concentration range at a working voltage of -0.33 V. The sensitivity is 3.39 mu A mu M-1 cm(-2), and the detection limit is 33 nM. The biosensor is fast, selective, well repeatable and reproducible, and therefore represents a viable platform for sensing bromate in aqueous samples.