In vivo monitoring neurotransmitters is one of the most crucial problems to solve for neuroscientist and chemists, because these substances, particularly the catecholamines have many physiological roles, are critical for normal neuronal metabolism, and are involved in some neurological disorders such as Parkinson's disease.
The fact that the catecholamines are easily oxidable compounds makes their detection possible by electrochemical methods. A major problem of electrochemical detection in real biological matrices is the coexistence of many interfering compounds. Among these, ascorbic acid is of particular relevance. For example, in the extracellular fluid (ECF) of central nervous system, this species is present in very high concentration and its oxidation potential is very close to those of the most common catecholamines.
The successful route to overcome problems with selectivity is to use a specific electrodic pretreatment that leads to the differentiation of oxidation signals. This approach involved laser activation, heat treatment or electrochemical preanodization or covering the electrodic surface, generally a carbon one, with an electroactive and permselective material exbiting electrocatalytic activity vs cathecholamines and repeling anionic species like ascorbate at physiological pH. The most relevant drawbacks is the low stability and sensitivity, the incomplete biocompatibility of the obtained sensors and the low reproducibility of the material performance.
Moreover, using diamond films modified electrodes it is possible to detect neurotransmitters in the presence of ascorbate at very low concentrations (50nM) but after a very strong anodic pre-treatment and the resulted sensor is stable for a relatively short time (up to 2 hours).
For the first time, we realized a new smart nanomaterial, based on nanostructured and functionalized TiO2 which allows the detection of catecholamines in cerebral fluids in the presence of physiological concentration of ascorbate without any material pre-treatment and with excellent performances of the resulted sensors in terms of stability, sensitivity and biocompatibility.
Investigating the structure and ion transport through the functionalized TiO2, we found that using this nanomatertial, it is possible to detect the most important neurotransmitters, at very low concentrations up to 10nM, selectively in the presence of ascorbic acid at a concentration over 3 order higher. Currently, the lack of neurotransmitters/ascorbic acid selectivity for electrochemical in-vivo detection of catecholamines presents a significant problem for monitoring brain activity. The utilization of functionalized oxide coatings enables a significant improvement in catecholamines selectivity, by suppressing the interference from oppositely charged electroactive ions. The combination of neurotransmitters selectivity and biocompatibility is essential for the design of long-term implantable neurological devices and for monitoring the activity of neuron cells. Thus real time measurements with practical and sensitive electrochemical tools could prove extremely useful for research into the etiology, therapy, and environmental modulators of disturbances related to neurotransmitters.
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