Direct electron transfer of horseradish peroxidase and its biosensor based on chitosan and room temperature ionic liquid

A reagentless horseradish peroxidase (HRP) biosensor, which is based on the direct electron transfer between the enzyme and the electrode, has been shown by direct electrochemistry of HRP and direct bioelectrocatalysis towards H2O2. Composite material based on biocompatible chitosan (Chi) and room temperature ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIM · BF4) was used to construct the HRP biosensor. A pair of stable and well-defined quasi-reversible redox peaks of HRP for the HRP(Fe(III))/HRP(Fe(II)) redox couple with a formal potential of about −0.34 V (vs. Ag/AgCl) in a pH 7.0 phosphate buffer solution (PBS) were observed at the Chi-BMIM · BF4-HRP composite film modified glassy carbon (GC) electrode. The biosensor exhibited good sensitivity and reproducibility, wide linear range, low detection limit and excellent long-term stability. The Chi-BMIM · BF4-HRP film was also characterized by UV–visible spectroscopy, indicating that HRP in the composite film could retain its native structure. Both biocompatibility of chitosan and inherent conductivity of BMIM · BF4 enable the composite material to become an excellent biosensing platform for realizing direct electrochemistry and electrocatalysis of HRP along with good stability.