pH-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)(6)(3-)/Fe(CN)(6)(4-)] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH3)(6)(3+)/Ru(NH3)(6)(2+) cationic redox analytes.