o-Phenylenediamine-Modified Carbon 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 microns 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 voltammetry 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 microM NO., o-PD electrodes displayed excellent linearity (R2 > or = 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 > or = 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.