Using poly(3-aminophenylboronic acid) thin film with binding-induced ion flux blocking for amperometric detection of hemoglobin A1c

This study reports a novel enzyme-free, label-free amperometric method for direct detection of hemoglobin A1c (HbA1c), a potent biomarker for diabetes diagnosis and prognosis. The method relies on an electrode modified with poly(3-aminophenylboronic acid) (PAPBA) nanoparticles (20-50 nm) and a sensing scheme named “binding-induced ion flux blocking.” The PAPBA nanoparticles were characterized by FT-IR, XPS, TEM, and SEM. Being a polyaniline derivative, PAPBA showed an ion-dependent redox behavior, in which insertion or extraction of ions into or out of PABPA occurred for charge balance during the electron transfer process. The polymer allowed HbA1c selectively bound to its surface via forming the cis-diol linkage between the boronic acid and sugar moieties. Voltammetric analyses showed that HbA1c binding decreased the redox current of PAPBA; however, the binding did not alter the redox potentials and the apparent diffusivities of ions. This suggests that the redox current of PAPBA decreased due to an HbA1c binding-induced ion flux blocking mechanism, which was then verified and characterized through an in situ electrochemical quartz crystal microbalance (EQCM) study. Assay with HbA1c by differential pulse voltammetry (DPV) indicates that the peak current of a PAPBA electrode has a linear dependence on the logarithm of HbA1c concentration ranging from 0.975 to 156 μM. The HbA1c assay also showed high selectivity against ascorbic acid, dopamine, uric acid, glucose and bovine serum albumin. This study has demonstrated a new method for developing an electrochemical HbA1c biosensor and can be extended to other label-free, indicator-free protein biosensors based on a similar redox polymer electrode.