Electrode materials for nitric oxide detection

Nitric oxide oxidation signals were compared for uniform test electrodes of platinum, iridium, palladium, rhodium, ruthenium, gold, graphite, and a ni ckel-porphyrin on graphite in deaerated phosphate-buffered saline (pH 7.0) at 35 degrees C. All tested materials detected NO. amperometrically, Curren t densities (A/M/cm(2) +/- S.D.) were Ir (0.021 +/- 0.002), Rh (0.088 +/- 0 .012), graphite (0.117 +/- 0.018), Pd (0.118 +/- 0.033), Au (0.149 +/- 0.03 9), Pt (0.237 +/- 0.117), Ni (II)-tetra(3-methoxy-4-hydroxyphenyl) porphyri n on graphite (0.239 +/- 0.009), and Ru (0.680 +/- 0.058). NO. oxidation cu rrent on ruthenium was maximal at 675 mV (vs Ag/AgCl), nearly three times t hat on the next-best materials, platinum and Ni-porphyrin on graphite poise d at 800 mV, The measured limit of detection for NO. on Ru was below 3 nM, Enhanced NO. oxidation current on ruthenium is apparently due to formation of nitrosyl-or chloronitrosyl-ruthenium complexes at the electrode surface. At fixed potentials above 675 mV, ruthenium exhibited an even larger NO. r esponse, characterized by current flow opposite in polarity to an oxidation , which we hypothesize reflects suppression of the oxidative background cur rent (presumably due to chloride oxidation or to the electrolysis of water) by a film consisting of nitrosyl- or chloronitrosyl-ruthenium complexes. T he sensitive response of the ruthenium electrode to the direct oxidation of NO. may be useful in sensors for biomedical applications. (C) 2000 Academi c Press.