The intrinsic redox reactions of polyamic acid derivatives and their application in hydrogen peroxide sensor

Polyamic acids (PAAs) containing benzothiazole (BT) and benzoxazole (BO) pendent groups (PAA-BT and PAA-BO, respectively) which possessed electroactivity were synthesized successfully. The addition of H2O2 chemically oxidized the intrinsic carboxylic acid groups of PAA to form peroxy acid groups, and the peroxy acid further oxidized the electroactive sites of BT and BO to form N-oxides. The N-oxides could be reverted to their original form by electrochemical reduction, thus increasing the electrochemical reductive current. Based on this mechanism, enzyme-free hydrogen peroxide (H2O2) biosensors were prepared by modifying gold electrodes with the PAA derivatives (PAA-BT/Au and PAA-BO/Au, respectively). These biosensors had rapid response times (3.9–5.2 s) and high selectivity and sensitivity (280.6–311.2 μA/mM-cm2). A comparison of the PAA-BT/Au and PAA-BO/Au electrodes with electrodes prepared using polyamide-BT or polyamide-BO (i.e., lacking the carboxylic acid groups) confirmed the mechanism by which PAA derivatives detect H2O2. Modifying the surface morphology of the electrode from a planar to a three-dimensional (3D) configuration enhanced the performance of the PAA-BO/Au electrode. The sensitivity of the 3D-PAA-BO/Au electrode was 1394.9 μA/mM-cm2, ∼4.5 times higher than that of the planar electrode. The detection limit was also enhanced from 5.0 to 1.43 μM. The biosensor was used analytically to detect and measure H2O2 in urine samples collected from healthy individuals and patients suffering from noninvasive bladder cancer. The results were promising and comparable to that measured by a classical HPLC method, which verified the developed biosensor had a potential to provide a usefully analytical approach for bladder cancer.