posted on 2019-01-03, 00:00authored byIsabel Álvarez-Martos, Arne Møller, Elena E. Ferapontova
Specific
analysis of such neurotransmitters as dopamine by the
aptamer electrodes in biological fluids is detrimentally affected
by nonspecific 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 nonspecific interfacial adsorption of serum and blood components.
We demonstrate that nonspecific 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 the (3.7 ± 0.3) × 104 M–1 s–1 found in PBS, and the dopamine
oxidation signal linearly depended on the dopamine concentration,
providing a sensitivity of analysis of 73 ± 3 nA μM–1 cm–2 and a 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,
otherwise most pronounced at positive electrode potentials used for
dopamine detection, and assist in designing more efficient antifouling
strategies for biomedical applications.