Films of manganese oxide nanoparticles with polycations or myoglobin from alternate-layer adsorption

Alternate adsorption of manganese oxide nanoparticles with polycations poly (dimethyldiallyl-ammonium) (PDDA) or myoglobin (Mb) onto silver, quartz, an d rough pyrolytic graphite gave stable, porous, ultrathin films. Quartz cry stal microbalance (QCM) and UV- vis absorbance revealed regular film growth at each adsorption step for MnO2 and PDDA and for SiO2 nanoparticles and M b. Scanning electron microscopy of MnO2/PDDA films showed smooth surfaces o n the 20 nm scale and cross sections consistent with individual nanoparticl es. QCM during growth of films of Mb and MnO2 reflected a competition for a dsorption of the protein by the film surface and dispersed MnO2 nanoparticl es. Nevertheless, films of Mb and MnO2 up to 30 nm thick on rough pyrolytic graphite electrodes could be constructed These novel films featured revers ible interconversion of the protein's heme Fe-III/Fe-II redox couple with 1 0 electroactive layers of protein, considerably more than for polyion-Mb fi lms on smooth gold (ca. 1.3 electroactive layers), and coiled PSS/Mb, films on rough graphite (7 electroactive layers). Shifts in redox potential caus ed by CO complexation of the heme Fen, BET specific areas, and electrochemi cally driven catalytic reduction of oxygen suggest that the Mb/MnO2 films a re highly porous to gas molecules. To our knowledge, these films represent the first nanofabrication of inorganic particles with functional proteins b y the layer-by-layer method.