PubMed Health⌕ Search

Biomedical subjects

Marcin Opallo

Publications and source records attributed to Marcin Opallo.

7 recordsLinked to original sources
PubMed2006

The effects of conductivity and electrochemical doping on the reduction of methemoglobin immobilized in nanoparticulate TiO2 films.

Methemoglobin (bovine) is immobilized from aqueous phosphate buffer (pH 5.5) solution into thin porous TiO(2) (anatase) films at ITO electrode surfaces. Films of TiO(2) are produced in a deposition process employing 40 nm diameter TiO(2) nanoparticles suspended in dry methanol followed by calcination. The pore size in these films is sufficient for methemoglobin (ca. 6 nm diameter) to diffuse into the porous structure (over several hours) and to remain immobilized in electrochemically active form. The electrochemical reduction of methemoglobin immobilized in TiO(2) and immersed in aqueous phosphate buffer at pH 5.5 is observed in two steps with (i) a small quasi-reversible voltammetric response at -0.16 V vs. SCE (Process 1) and (ii) an irreversible reduction peak at ca. -0.5 V vs. SCE (Process 2). The irreversible response is recovered only after slow chemical re-oxidation of hemoglobin to methemoglobin. At sufficiently negative applied potential "electrochemical doping" of the TiO(2) host is observed to lead to a considerably enhanced reduction Process 1. TiO(2) can be temporarily switched from a non-conducting (irreversible electron transfer) into a conducting (reversible electron transfer) state.

Adsorption↗
PubMed2005

TiO2 phytate films as hosts and conduits for cytochrome c electrochemistry.

Cytochrome c is accumulated into a film of TiO(2) nanoparticles and phytate by adsorption from an aqueous solution into the mesoporous structure. Stable voltammetric responses and high concentrations of redox protein within the TiO(2) phytate layer can be achieved. Two types of electrode systems are reported with (i) the modified TiO(2) phytate film between electrode and aqueous solution phase and (ii) the modified TiO(2) phytate film buried under a porous gold electrode ('porotrode'). The electrical conductivity of TiO(2) phytate films is measured and compared in the dry and in the wet state. Although in the dry state essentially insulating, the TiO(2) phytate film turns into an electrical conductor (with approximately 4 Omega cm specific resistivity assuming ohmic behaviour) when immersed in aqueous 0.1 M phosphate buffer solution at pH 7. The redox protein cytochrome c is therefore directly connected to the electrode via diffusion and migration of electrons in the three dimensional mesoporous TiO(2) phytate host structure. Electron transfer from cytochrome c to TiO(2) is proposed to be the rate-determining step for this conduction mechanism.

Cytochromes c↗
PubMed2005

Ion transfer processes at 4-(3-phenylpropyl)-pyridine/aqueous electrolyte/electrode triple phase boundary systems supported by graphite and by mesoporous TiO2.

Biphasic electrode systems allow electrochemical reactions to be driven in a microphase of organic liquid (typically 1-100 nL), which is coupled via ion transfer processes to the surrounding aqueous electrolyte medium. Microdroplet deposits on basal plane pyrolytic graphite as well as thin film deposits of the organic phase within a mesoporous titanium oxide host film are investigated. Cobalt tetraphenylporphyrin (CoTPP) is dissolved in the organic liquid 4-(3-phenylpropyl)-pyridine (PPP) and deposited in the form of microphases at suitable electrode surfaces. The electrode is immersed in aqueous electrolyte environments. It is shown that two stable and highly reversible one-electron metal-centred redox processes occur consistent with Co(III/II)TPP and Co(II/I)TPP in the presence of axial pyridine ligands. The electrochemical characteristics for both processes are strongly affected by the liquid/liquid ion exchange accompanying the redox processes. The potential for both the Co(III/II)TPP and the Co(II/I)TPP redox processes can be adjusted independently by the choice of the nature and concentration of the aqueous electrolyte. The reversible potential observed for the CoTPP metal complex is dominated by the Gibbs energy of transfer for the 'spectator ions'. Conditions can be chosen to eliminate ion transfer effects on the potential scale for biphasic oxidation and reduction processes.

Journal Article↗
PubMed2004

Hydrophobic silica sol-gel films for biphasic electrodes and porotrodes.

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.

Journal Article↗
PubMed2004

Liquid / liquid ion-transfer processes at the dioctylphosphoric acid (N,N-didodecyl-N',N'-diethylphenylenediamine) / water (electrolyte) interface at graphite and mesoporous TiO2 substrates.

Biphasic electrode systems are studied for the case of the oxidation of the water-insoluble liquid N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD) neat and dissolved in bis(2-ethylhexyl) phosphate (HDOP) and immersed in aqueous electrolyte media. The oxidation process in the absence of HDOP is accompanied by transfer of the anion (perchlorate or phosphate) from the water into the organic phase. However, in the presence of HDOP, oxidation is accompanied by proton exchange instead. This electrochemically driven proton exchange process occurs over a wide pH range. Organic microdroplet deposits of DDPD in HDOP at basal plane pyrolytic graphite electrodes are studied by voltammetric techniques and compared in their behavior to organic microphase deposits in mesoporous TiO2 thin films. The mesoporous TiO2 thin film acts as a host for the organic liquid and provides an alternative biphasic electrode system compared to the random microdroplet/graphite system. Two types of mesoporous TiO2 thin-film electrodes, (i) a 300-400-nm film on ITO and (ii) a 300-400-nm film on ITO sputter-coated with a 20-nm porous gold layer, are investigated.

Electrochemistry↗
PubMed2002

Carbon ceramic electrode modified with redox liquid.

A carbon ceramic electrode modified with a redox liquid, butylferrocene, exhibiting in aqueous salt solution electrochemical behaviour resulting from the redox process of the modifier and ion transfer across the liquid-liquid interface has been prepared.

Biosensing Techniques↗