A novel polybenzimidazole-modified gold electrode for the analytical determination of hydrogen peroxide

The imine of polybenzimidazole (PBI) is chemically oxidized by hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopies (XPS) showed that when the AcOH concentration remained constant, the degree of oxidation increased with increasing H₂O₂ levels. Moreover, the imine also exhibited electrochemical redox behavior. Based on these properties, a PBI-modified Au (PBI/Au) electrode was developed as an enzyme-free H₂O₂ sensor. At an applied potential of -0.5 V vs. Ag/AgCl, the current response of the PBI/Au electrode was linear with H ₂O₂ concentration over a range from 0.075 to 1.5 mM, with a sensitivity of 55.0 μA mM^-1 cm^-2. The probe had excellent stability, with <5% variation from its initial response current after storage at 50 °C for 10 days. Potentially interfering species such as ascorbic or uric acid had no effect on sensitivity. Sensitivity improved dramatically when multiwalled carbon nanotubes (MWCNT) were incorporated in the probe. Under optimal conditions, the detection of H₂O₂ using a MWCNT-PBI/Au electrode was linear from 1.56 μM to 2.5 mM, with a sensitivity of 928.6 μA mM^-1 cm^-2. Analysis of H ₂O₂ concentrations in urine samples using a MWCNT-PBI/Au electrode produced accurate real-time results comparable to those of traditional HPLC methods.