Reduced graphene oxide decorated with metals nanoparticles electrode as electrochemical sensor for dopamine

Dopamine (DA) is one of the most important neurotransmitters that influences the processes that involve memory, sleep, mood, learning among others [1]. In fact, in the last years, dopamine concentration in human body fluids has been related to some neurodegenerative diseases, such as Parkinson and Alzheimer's diseases [2]. The possibility to have a bio-marker for these disease is of extreme importance because, disease related with dementia, are diagnosed when they are already developed and their management become almost impossible. The possibility to continuously monitor DA level in fluids, such as blood and urine, could accelerate the early diagnosis of these diseases. The principal analytical method to detected dopamine is High Pressure Liquid Chromatrography (HPLC), but this technique does not allow any kind of real time or in situ analysis and, furthermore, is highly expensive and hard to use [3] - [4]. To achieve a real-time screening of DA, electrochemical sensors are perfect candidates [5]. In this work we show the preliminary results concerning the development and the optimization of a flexible and cheap electrochemical DA sensor. The active material of sensors is based on reduced graphene oxide with Au nanoparticles (NPs) and was obtained by co-electrodeposition into a ITO-PET substrate. The electrodeposition parameters have been optimized in order to increase the DA peak in Phosphate Buffer Solution (PBS) and obtain a Limit Of Detection (LOD) in the nM range. A very wide linear range (0.1-30 μM) and a low LOD, down to 50 nM, have been found. The main issue to electrochemically detect dopamine concern the presence of other compounds able to react on the surface of the electrode, leading overlapping peak [6-9]. Ascorbic acid (AA) and Uric Acid (UA), two of these interference species, have oxidation peak of about 0.1 V and 0.4 V, respectively [10]. Furthermore, in biological samples, these chemicals are present in a concentration range of about 100-1000 times higher than dopamine one, making this issue even more challenging [10]. We found by voltammetry studies that in presence of all these chemicals (AA,UA and DA) DA can be still detected. Moreover, we found that is possible to use our electrode to quantify even UA at low concertation. In order to validate the technology, the sensor was also tested using synthetic urine and cerebrospinal fluid, from a patient with alcoholic neuropathy. Excitingly, we have found that both these matrixes don't interfere with DA detection (or in a negligible way). The results of this work are so really promising and thrilling because can allow a in-situ, low cost and real time screening of DA to permits early diagnosis of different diseases.