Dopamine, chemically known as 3,4-dihydroxyphenyl ethylamine, is a chemical found naturally in the human body. A dopamine deficiency occurs due to a loss of dopamine amount that it caused by a problem with the receptors in the brain. The most common conditions linked to a lack of dopamine include depression, Schizophrenia, and Parkinson's disease. In Parkinson's disease, It is a loss of the nerve cells in a specific part of the brain resulting in a lack of dopamine in the same area. Thus, the quantitative determination of this neurotransmitter appears to be important for diagnosis, monitoring, and pharmacological intervention. Dopamine can be diagnosed using various advanced techniques such as High-Performance Liquid Chromatography (HPLC), chemical luminescence, Ultraviolet-visible spectroscopy (UV-Vis) and gas chromatography-mass spectrometry (GC). Although these strategies techniques are effective for the detection of dopamine, there are still some drawbacks, such as time-consuming, low sensitivity and expensive equipment. It is possible to detect dopamine using a modified electrode for diagnosing these diseases. Compared with these techniques, electrochemical determination of DA has acknowledged extensive attention since it allows for fast, simple, decisive and cost-effective way together with super-high sensitivity.
In this work, a biosensor for dopamine determination was developed with a popular sensitive and selective enzymatic method was applied. Tyrosinase (Tyr), also known as polyphenol oxidase, is a divalent copper ion with the enzyme protein binding of metal enzymes. The important point in the development of Tyr biosensor is an effective method to hold of Tyr on the electrode surface. For biosensing electrodes, Au nanoparticle is an excellent choice due to its conductivity, stability, biocompatibility and large surface area. According to their good physical and chemical properties, gold, nanoparticles (AuNPs) and Carbon Nanotubes (CNTs) were applied. It is found that AuNPs has excellent conductivity, high surface area, and catalytic properties. Carbon nanotubes (CNTs) are formed by rolling graphite sheets and have quasi-one-dimensional (1D) structures. It can be used for promoting electron transfer between the electroactive species and electrode, high chemical stability, high surface area, strong adsorption ability, and excellent biocompatibility5. Moreover, some polymer materials are applied for the combination with other kinds of materials. Poly(diallydimethylammonium chloride) (PDDA) was utilized to synthesize PDDA capped AuNPs (PDDA@AuNPs), a polymer with high electrical conductivity and ionic strength, was electrochemically deposited on the electrode surface. These materials are used for the development of dopamine biosensors which become accurate, simple, inexpensive and fast for analysis.