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.

Miniaturised liquid/liquid interfaces provide benefits for bioanalytical detection with electrochemical methods. In this work, microporous silicon membranes which can be used for interface miniaturisation were characterized by simulations and experiments. The microporous membranes possessed hexagonal arrays of pores with radii between 10 and 25 µm, a pore depth of 100 µm and pore centre-to-centre separations between 99 and 986 µm. Cyclic voltammetry was used to monitor ion transfer across arrays of micro-interfaces between two immiscible electrolyte solutions (µITIES) formed at these membranes, with the organic phase present as an organogel. The results were compared to computational simulations taking into account mass transport by diffusion and encompassing diffusion to recessed interfaces and overlapped diffusion zones. The simulation and experimental data were both consistent with the situation where the location of the liquid/liquid (l/l) interface was on the aqueous side of the silicon membrane and the pores were filled with the organic phase. While the current for the forward potential scan (transfer of the ion from the aqueous phase to the organic phase) was strongly dependent on the location of the l/l interface, the current peak during the reverse scan (transfer of the ion from the organic phase to the aqueous phase) was influenced by the ratio of the transferring ion's diffusion coefficients in both phases. The diffusion coefficient of the transferring ion in the gelified organic phase was ca. nine times smaller than in the aqueous phase. Asymmetric cyclic voltammogram shapes were caused by the combined effect of non-symmetrical diffusion (spherical and linear) and by the inequality of the diffusion coefficient in both phases. Overlapping diffusion zones were responsible for the observation of current peaks instead of steady-state currents during the forward scan. The characterisation of the diffusion behaviour is an important requirement for application of these silicon membranes in electroanalytical chemistry.