It is well known that red blood cell (RBC) membranes are charged negatively and surrounded by an electric double layer (EDL). The electrochemical nature of blood cell interaction with foreign materials that are electrical conductors is due to the interaction of blood cell EDL with the foreign material. Numerous investigations of the above systems have led to a hypothesis of charge transfer occurring between the cell and the electrode [1]; however, there has been no experimental corroboration of this phenomenon to date.

The present work attempted to bridge this gap by investigating the electrochemical behavior in the Pt/RBC system in isotonic (physiologic) saline solution (aqueous 0.15 M NaCl), where the above solution served as the background electrolyte. Erythrocyte suspension for experiments was prepared from donor whole blood by centrifugation using a CR 3.12 (Jouan, France) centrifuge at 4-6 °C and 1500 g. The erythrocytes were subsequently washed with isotonic physiologic saline to remove residual blood plasma. Erythrocyte counts in suspensions were measured using a Beckman Coulter AcT Diff 2 hematology analyzer. Erythrocyte counts in suspensions used in the electrochemical cell were 4.0×10¹² L^–1.

Polarization and microcoulometric measurements were performed with an IPC Pro L potentiostat (ZAO «Kronas») in a three-electrode electrochemical cell, with the cathodic and anodic chambers separated by a polypropylene porous membrane. A platinum microelectrode and platinum wire mesh were used as the working and counter electrode, respectively. Potentials were measured against a saturated silver/silver chloride reference electrode.

For microcoulometric measurements, the electrochemical cell was filled with the above background electrolyte, and the platinum electrode was polarized to a set potential for 30 min; subsequently, the erythrocyte suspension was added to the background electrolyte, and microcoulometric data were recorded for 30 min. Oxygen was removed from the background electrolyte by the addition of Na₂SO₃ to a final sulfite concentration of 0.02 M in the electrochemical cell. The residual quantity of Na₂SO₃ was monitored in the cell via the sulfite/sulfate anode oxidation peak.

A considerable difference in the charge Q was found to be required to maintain the same cathode potential of Pt electrode in the background electrolyte and in the background electrolyte containing the RBC suspension, with the difference between those measured values (ΔQ= Q_saline – Q_saline+RBC) varying depending on the working electrode potential (Fig. 1(a)). It turned out that a similar phenomenon occurs in the anodic range (Fig. 1(a)). Thus, electrochemical activity of erythrocytes in isotonic saline was shown at the platinum electrode for cathode potentials more negative than E = –150 mV, and for anode potentials more positive than E= +200 mV. This observation is very important because it provides the first experimental corroboration of electron transport between the electrode and erythrocytes.

It should also be emphasized that electrochemical processes were not observed between –150 mV and +200 mV (no changes of charge Q), which indicates relative indifference of the electrode material with respect to the erythrocytes.

Additionally, electron transport without polarization was observed on the Pt electrode. It was observed that open-circuit potential (OCP) values of Pt in isotonic saline changed with the addition of RBC suspension to saline. These data for the Pt electrode are shown in Fig. 1(b). Negative shifts of OCP for Pt electrode were observed after a addition of RBC suspension to saline with ∆E= 106 mV. This phenomenon can be rationalized by the leveling of charge densities of erythrocyte membranes and electrode surface in the electrostatic field of the [electrode/erythrocyte] system. Thus, electron transport occurred from the erythrocyte membrane to the electrode.

Reference

[1] Sawyer P. N. et al. Electrochemical Aspects of Thrombogenesis-Bioelectrochemistry Old and New // Journal of The Electrochemical Society. – 1974. – V. 121. – №. 7. – P. 221C-234C.