DOPAMINE ELECTROCHEMICAL SENSOR BASED ON REDUCED GRAPHENE OXIDE AND METAL NANOPARTICLES

Abstract

Dopamine (DA) is one of the most important neurotransmitters released from the brain, and is involved in many different biological processes. This neurotransmitter influences the processes that involve memory, sleep, mood, learning, and so on. Besides, in the last years, dopamine concentration in human body fluids has been related to some neurodegenerative pathologies, such as Parkinson and Alzheimer’s diseases [1]. It is well known that these pathologies are due to the formation of amyloids plaques that block part of the brain. Many literature data reports that DAergic neurons (areas of midbrain where DA is synthesized) shows a different activity when amyloid plaques are present with a consequent release of a different amount of DA during the development of these pathologies [2]. Despite the involvement of DA in dementia is still under debate, the possibility to have a bio-marker for these diseases is of extreme importance. In fact nowadays, diseases related to dementia are diagnosed when they are already developed so that their management is almost impossible. The possibility to continuously monitor DA concentration in fluids such as blood and urine, can be a valid help to accelerate the early diagnosis of these diseases. The principal analytical methods currently used to detect dopamine are Enzyme Linked ImmunoSorbet Assay (ELISA) and High Pressure Liquid Chromatography (HPLC). Through these methods, it is possible to reach different LOD depending on the analyzed medium, such as 0.05 µM in the case of urine and 0.5 µM for plasma. Despite these techniques are highly performant (low LOD, high selectivity and sensitivity), they are expensive, hard to handle, and time consuming. All these drawbacks make the screening of DA difficult to be achieved. In fact, the sample has to be collected by the patient and sent to the lab that after many days, will give the result. To achieve a real-time screening of DA, electrochemical sensors are ideal candidates. Indeed, just a cheap battery is requested for such a sensor, so that the system is small and portable, compared to HPLC or ELISA, which are big analytical machines. The electrodes fabrication is cheap, reproducible and fast. The features of these sensors are good enough to compete with the standard techniques. The main disadvantage of this technique is the interference from uric acid (UA) and ascorbic acid (AA, vitamin C). These compounds are always present in body fluids and have redox potential close to the DA one. This make the detection of DA harder because the peaks of AA and UA can overlap with the DA one. Therefore, it is necessary to develop a sensor with electrochemical active materials that present a high selectivity to DA in comparison to AA and UA. 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 is based on reduced graphene oxide mixed with either Au or Pt nanoparticles (NPs), and it was obtained by co-electrodeposition on ITO-PET substrate (Figure 1a). The electrodeposition parameters, such as concentration, deposition time and potential have been optimized in order to increase the DA peak and to obtain a low LOD, in the nM range (Figure 1b). The detection of DA was performed by square wave voltammetry and linear cyclovoltammetry. The sensors were also tested using synthetic urine (in order to simulate a real sample where DA concentration is usually lower than 500 nM). Preliminary results show: i) negligible interference from ascorbic and uric acid, ii) very wide linear range, and iii) low LOD. The current findings are very satisfying, suggesting to start a pre-screening of dementia related diseases.