Thermally Induced Transient Activity Changes of Plasmin Adsorbed onto Bare and Fibrinogen-Modified Graphite and Glassy Carbon Surfaces

The occurrence of a thermally induced first-order transition affecting the amidolytic activity of plasmin adsorbed onto bare and protein-modified graphite and glassy carbon was demonstrated in the 10-45 degrees C temperature range in the presence of a chromogenic substrate. Modification of the surfaces was achieved upon spontaneous adsorption of plasmin to surfaces bearing a coating of fibrinogen, whether electrochemically oxidized or not. The amount of fibrinogen adsorbed at graphite was determined by ELISA. The kinetics of the transition was characterized by its starting temperature (T(c)), which was between 14 and 19 degrees C, the first-order rate constant, and the activation energy E(a) deduced from Arrhenius plots. Results showed the absence of a correlation between T(c), E(a), and contact angle variations. It is therefore likely that these variables address separate steps in a complex pathway of reactions undergone by plasmin under mild thermal constraints. Copyright 2001 Academic Press.     

Ionic wind generator derived from a liquid filled capillary pin. Application to particle capture

A new fluid pin-based ionic wind generator applied to airborne pathogen collection combines the processes of air flow generation by ionic wind, electrospray and electrostatic particle collection. This new concept brings a breakthrough in integration as it combines these three phenomena with a single driving force in order to perform the four functions of an airborne pathogen sampler, namely air flow production, particle capture, sample phase transfer and collecting electrode decontamination. The characterizations presented in this article led to a proof of concept and demonstrated the device's performance for a compact and portable airborne pathogen collection system.     

pHh-dependent permselectivity of the fibrinogen-modified carbon paste electrode

The modification of carbon paste matrices with fibrinogen is reported. The effect of the pH of the solution on the CV peak currents of positively or negatively charged redox analytes was examined at the fibrinogen-modified carbon paste electrode. In the presence of the coating, pH-dependent selectivity in electrochemical detection of charged species was demonstrated depending on the sign of the supported charge. Above the isoelectric pH attributed to the immobilized protein (5.5), the current response of anionic redox probes [Fe(CN)/Fe(CN)] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH₃)/Ru(NH₃) cationic redox analytes.     

Effect of surface activation on charge and mass transfer rates of the hexacyanoferrate(III)/(II) redox probe at fibrinogen-modified carbon paste electrodes

The electron transfer and mass transport properties of fibrinogen-modified carbon paste surfaces, following preliminary activation for various duration, has been studied using cyclic voltammetry (CV) and chronoamperomety. Activation was carried out by subjecting the surface, exposed to a solution-containing oxidant species, to positive polarization of increasing duration. Modification was subsequently achieved following spontaneous adsorption of fibrinogen on exposure to a solution containing the protein. To investigate the electrochemical properties of this surface, the variations in the charge-transfer and mass-transport kinetics of hexacyanoferrate(III)/(II) ions, used as a redox probe, were analyzed separately. The results showed the favorable effect of activation on electrocatalysis and charge-transport properties through the coating. Relative to pretreated bare surfaces, however, the presence of fibrinogen induced opposed variations, thus explaining unchanged CV peak currents. These features were essentially attributed to morphological changes promoted by activation in the protein layer.