Interactions of proteins with small ionised molecules: electrochemical adsorption and facilitated ion transfer voltammetry of haemoglobin at the liquid|liquid interface

The interaction of proteins with interfaces and surfaces provides a basis for studying their behaviour and methods to detect them. This paper is concerned with elucidation of the mechanism of electrochemical detection of haemoglobin (Hb) at the interface between aqueous and organic electrolyte solutions. The adsorption of Hb at the interface was investigated by alternating current (AC) voltammetry. It was found that addition of Hb to the aqueous phase induced a shift of the potential of zero charge at the liquid|liquid interface, due to interfacial adsorption of Hb. The influence of the nature and the concentration of the organic phase electrolyte on the electrochemical signal was investigated by cyclic voltammetry (CV). It was found that the electrochemical signal, in the presence of aqueous phase Hb, was due to the facilitated transfer of the anion of the organic phase electrolyte to the aqueous phase. The transfer current was dependent on both the nature and concentration of the organic phase electrolyte anion. These results confirm that adsorbed Hb molecules at the liquid|liquid interface interact with small ionised molecules and facilitate their transfer across the interface. The results will provide a basis for both biomolecular detection methods and for the study of protein–small ionised molecule interactions.