Periodic Reporting for period 1 - eADAM (Ultra-small electrochemical aptasensors for specific dopamine real-time monitoring)
Reporting period: 2016-02-01 to 2018-01-31
A large number of these disorders (e.g. Parkinson’s and Alzheimer’s diseases, schizophrenia, drug addiction, or psychosis) are correlated with abnormal fluctuations in the levels of dopamine (a small molecule neurotransmitter secreted by the neurons in the brain). Therefore, it is not surprising that dopamine occupies a central piece in the current neuroscience research, aiming to understand the mechanism of the disease development and early diagnosis.
The intrinsic electroactive nature of dopamine makes electrochemical methods very well suited for its monitoring. However, other co-existing molecules, such as nor/epinephrine, L-DOPA, catechol or ascorbic acid, provide signals in the range of potentials where dopamine is oxidized, thereby questioning the chemical selectivity of the measurements. The overall objective of this project was to develop electrochemical tools that ensure the specific measure of dopamine by this contributing to redefine the way dopaminergic diseases are monitored and treated.
We also demonstrated that the replacement of the RNA bases by their DNA analogues destroys the aptamer specificity of biorecognition and binding of dopamine, providing the same response as a DNA mutated sequence with destabilized dopamine-binding region.
We explored the possibility of using redox-labelled dendrimers as wires to improve sensitivity. This resulted to be a particularly interesting system, where the electron transfer (ET) mechanism was strongly influenced by the nanostructure arrangement at the electrode surface. In the case of diluted layers, the ET followed the features of a surface-confined reaction that occurs by electron tunneling, while in compact monolayers the mechanism of ET formally switched to a diffusion-controlled process. This was attributed to the strong interactions existing between the neighboring dendrimers, which restricted their motional freedom and affected their conformational state on the electrode surface.
The next step in the project was to adapt the specific dopamine sensor for implantation in Drosophila flies and for that, carbon materials resulted to be more adequate. We found that the electrochemical reactions of dopamine and related catecholamines were slowed down both kinetically and thermodynamically at electrode materials with graphite-layered structure. Interestingly, the reactions proceeded at different potentials, so by using amperometry it was possible to discriminate dopamine from interferents in both cerebrospinal and hemolymph-like fluids. The microelectrodes were finally used for implantation and dopamine recordings in Drosophila flies.
The overall scientific outcome from the project was deposited in the open access repository PURE and disseminated to:
- The scientific community through 5 high-impact factor peer reviewed publications and 4 oral presentations at international conferences.
- The public through volunteer lectures.