3 research outputs found
Electrochemical, spectrophotometric, electroanalytical and electrochemical quartz crystal microbalance studies of some redox-active films
Redox films are a broad class of electrochemically active films with many potential
uses. In the present work, Prussian Blue and carbon coated electrodes have been
investigated as possible electrochemical sensors for ascorbic acid and pH, respectively.
The potential of Prussian Blue as an optical sensor has also been investigated.
In the case of Prussian Blue, it has been discovered that up to 100 monolayers can be
systematically deposited on gold electrodes by a new technique that we have called
"directed assembly". This provides control of layer thickness with nanometer
precision.
In the case of carbon coated electrodes, we have developed a mechanical coating
technique for quartz crystals, which allows them to be used in electrochemical cells,
simultaneously as working electrodes and as mass sensors in a quartz crystal
microbalance. This opens up the possibility of developing a variety of new sensor
technologies, including pH-sensitive microelectrodes
The direct electrochemistry of ferritin compared with the direct electrochemistry of nanoparticulate hydrous ferric oxide
Horse spleen ferritin is a naturally occurring iron storage protein, consisting of a
protein shell encapsulating a hydrous ferric oxide core about 8 nm in diameter. It is
known from prior work that the protein can be adsorbed onto the surface of tin-doped
indium oxide (ITO) electrodes, where it undergoes voltammetric reduction at about
–0.6 V vs Ag/AgCl. This is accompanied by dissolution of Fe(II) through channels in
the protein shell. In the present work, it is demonstrated that a pre-wave at about –0.4
V vs Ag/AgCl is due to the reduction of FePO4 also present inside the protein shell.
In order to prove that the pre-wave was due to the reduction of FePO4, it was first
necessary to prepare 8 nm diameter hydrous ferric oxide nanoparticles without protein
shells, adsorb them onto ITO electrodes, and then study their electrochemistry.
Having achieved that, it was then necessary to establish that their behaviour was
analogous to that of ferritin. This was achieved in several ways, but principally by
noting that the same electrochemical reduction reactions occurred at negative
potentials, accompanied by the dissolution of Fe(II). Finally, by switching to aqueous
phosphate buffer, the pre-wave could be unambiguously identified as the reduction of
FePO4 present as a thin layer on the hydrous ferric oxide nanoparticle surfaces.
Although the bare and protein-coated hydrous ferric oxide nanoparticles were found
to behave identically toward electrochemical reduction, they nevertheless reacted very
differently towards H2O2. The bare nanoparticles acted as potent electrocatalysts for
both the oxidation and the reduction of H2O2, whereas the horse spleen ferritin had a
much lesser effect. It seems likely therefore that the protein shell in ferritin blocks the
formation of key intermediates in hydrogen peroxide decomposition
Directed assembly of multilayers: the case of Prussian Blue
We introduce the concept of ‘directed assembly’ of multilayers on surfaces: the overall process involves the exposure of a surface to a series of solutions containing, alternately, adsorbable cations and adsorbable anions, and these are gradually built up into well-defined multilayer structures