O-phenylenediamine-modified fiber electrodes for the detection of nitric oxide

Nitric oxide (NO^.) sensors were prepared using o-phenylenediamine (o-PD) and Nafion to modify the surface of 30 μm diameter carbon fiber electrodes. These electrodes were compared with nickel porphyrin-type NO^. sensors that have already been described. High-speed chronoamperometry, amperometry, and differential pulse voltammetty were used to compare the performance of sensors modified with various combinations of Nafion, o-PD, or nickel(II) meso-tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin (Ni-TMPP), in order to determine which electrodes had the most sensitivity and selectivity for NO^.. Our findings showed that electrodes treated with Nafion first, followed by o-PD, were very sensitive to NO^., with a detection limit of 35 ± 7 nM. In addition, o-PD electrodes were also very selective against ascorbate (>600:1), dopamine (>300:1), and nitrite (>900:1). Moreover, in the range of 0-6 μM NO^., o-PD electrodes displayed excellent linearity (R² ≥ 0.997). In contrast, Ni-TMPP electrodes (with Nafion) had significantly poorer detection limits (76 ± 12 nM) and were less selective against dopamine (<5:1) and nitrite (<200:1). Ni-TMPP electrodes were also less linear than o-PD electrodes (R² ≥ 0.911). Finally, we tested the in vitro and in vivo performance of the o-PD electrode in terms of its ability to detect NO^. release from isolated rat renal arterioles and to measure NO^. diffusion in the extracellular space of the rat brain.