Detection of haemoglobin using an adsorption approach at a liquid-liquid microinterface array.

The behaviour of haemoglobin (Hb) at the interface between two immiscible electrolyte solutions (ITIES) has been examined for analytical purposes. When Hb is fully protonated under acidic conditions (pH <pI) in the aqueous phase, it undergoes a potential-dependent adsorption and complexation, at the interface, with the anions of the organic phase electrolyte. When utilised as a simple and fast preconcentration step, consisting of adsorbing the protein at the interface, in conjunction with voltammetric desorption, this opens up the ITIES to the adsorptive stripping voltammetry approach. Utilising a 60 s adsorption step and linear sweep voltammetry, a linear response to Hb concentration in aqueous solution over the range 0.01-0.5 μM was achieved. The equation of the best-fit straight line was I(p) = 7.46 C - 0.109, R = 0.996, where I(p) is the peak current (in nanoampere) and C is haemoglobin concentration (in micromolar). The calculated detection limit (3σ) was 48 nM for a 60 s preconcentration period, while the relative standard deviation was 13.3% for six successive measurements at 0.1 μM Hb. These results illustrate the prospects for simple, portable and rapid label-free detection of biomacromolecules offered by electrochemistry at arrays of liquid-liquid microinterfaces.