A stable Fe(4-TMPyP)-DNA-PADDA (FePyDP) film was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between water-soluble iron(Ill) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(4-TMPyP)) and DNA template, where PADDA (poly(acrylamide-co-diallyldimethylammonium chloride)) is employed as a co-immobilizing polymer. Electronic absorption spectral and quartz crystal microbalance measurements revealed that Fe(4-TMPyP) interacted with DNA to generate a species with the molar ratio of 1:5 for Fe(4-TMPyP):DNA phosphate. Cyclic voltammetry of FePyDP film showed a pair of stable and reversible peaks corresponding to Fe-III/Fe-II redox potential of -0.13 V versus Ag\AgCl in pH 7.4 PBS. The electron transfer was expected across the double-strand of DNA by an "electron tunneling" mechanism. The modified electrode displayed an excellent catalytic activity for NO reduction at -0.61 V versus Ag\AgCl. The catalytic current was enhanced at lower pH. Chronoamperometric experiments demonstrated a rapid response to the reduction of NO with a linear range from 0.1 to 90 muM. The detection limit was 30 nM at a signal-to-noise ratio of 3. (C) 2004 Elsevier Ltd. All rights reserved.