Dopamine Binding and Analysis in Undiluted Human Serum and Blood by the RNA-Aptamer Electrode

摘要： Specific analysis of such neurotransmitters as dopamine by the aptamer electrodes in biological fluids is detrimentally affected by non-specific adsorption of media, particularly pronounced at positive charges of the electrode surface at which dopamine oxidizes. Here, we show that dopamine analysis at the RNA-aptamer/cysteamine-modified electrodes is strongly inhibited in undiluted human serum and blood due to non-specific interfacial adsorption of serum and blood components. We demonstrate that non-specific adsorption of serum proteins (but not of blood components) could be minimized when analysis is performed in a flow and injections of serum samples are followed by washing steps in a phosphate buffer solution (PBS) carrier. Under those conditions, the dopamine-aptamer binding affinity in whole human serum of (1.9±0.3)×104 M-1 s-1 was comparable to (3.7±0.3)×104 M-1 s-1 found in PBS, and the dopamine oxidation signal linearly depended on the dopamine concentration, providing the sensitivity of analysis of 73 ± 3 nA μM-1 cm-2 and the LOD of 114 ± 8 nM. The flow-injection apatmer-electrode system was used for direct analysis of basal levels of dopamine in undiluted human serum samples, without using any physical separators (membranes) or filtration procedures. The results suggest a simple strategy for combatting biosurface fouling most pronounced at positive electrode potentials and assist in designing more efficient antifouling strategies for biomedical applications.