In-Situ Direct Electrochemistry of Hemoglobin Using Vertically Aligned Carbon Nanotube Ropes

Abstract

Direct electrochemistry of hemoglobin (Hb) is usually implemented by immobilizing it on the electrode. In-situ determination of Hemoglobin is little bit tough due to slow electron transfer in solution phase owing to its complex structure. In this study, we report in-situ direct electrochemistry of hemoglobin using vertically aligned single walled carbon nanotubes (SWNTs) ropes on indium tin oxide (ITO) platform. Morphological characterization of aligned SWNTs is accomplished using optical surface profiler, FE-SEM and AFM. Electrochemical impedance spectroscopy (EIS) of SWNT/ITO electrode reveals reduction in 'charge transfer resistance' for SWNT/ITO electrode in comparison to ITO. Exchange current density increases tenfold (5.4 × 10-2 A cm-2 while standard rate constant increases hundred times (1.2 × 10-4 C2s-1 cm-2 after vertical alignment of SWNTs on ITO sur- face. Cyclic voltammetry (CV) of Hb demonstrates tenfold increase in the currents after SWNT immobilization. Kinetic studies using CV revel surface controlled nature of the reaction that is attributed to concentration of Hb molecules in close proximity of the electrode, which in turn is due to negatively charged carboxyl ends of aligned carbon nanotubes. Moreover, a plausible mechanism for increase of peak currents in acidic pH range is also presented that clearly demonstrates the role of oxygen containing groups at the carbon nanotube ends for direct electron transfer from hemoglobin. Sensitivity of the sensor is determined for both lyophilized Hb and that present in red blood cells (RBCs) separated from whole blood. It is found to be 21.2 μAμM-1 and 8.94 μAdLg-1 respectively. Lower detection limit of hemoglobin is found to be 10 nM. After successful demonstration of aligned carbon nanotubes (CNTs) in solution phase electrochemistry of hemoglobin, SWNT/ITO electrodes can be used for routine clinical determination of hemoglobin in whole blood samples using RBCs