Mohadeseh Safaei - Department of Chemistry, Faculty of Sciences, Islamic Azad University, Yazd Branch, Yazd, Iran
Hadi Beitollahi - Environment Department, Institute of Science and High Technology and Environmental Sciences, Graduate Universityof Advanced Technology, Kerman, Iran
Masoud Reza Shishehbore - Department of Chemistry, Faculty of Sciences, Islamic Azad University, Yazd Branch, Yazd, Iran

Electroanalytical methods have attracted more attention in recent years for environmented and biological compound determination due to their sensitivty, accuracy, low cost and simplicity [1]. Levodopa (LD) (a precursor of DA) is an important neurotransmitter, which is used for the medication of neural disorders such as Parkinson’s disease[1]. People with Parkinson’s disease have depleted levels of dopamine and levodopa is used to increase dopamine in the brain, which reduces the symptoms of Parkinson’s disease[2]. Tryptophan (TRP) is an essential amino acid withvarious physiological roles[3]. TRP is commonly synthesized in plants and microorganisms from shikimic acid[4]. The improper metabolite of TRP leads to abnormal levels of melatonin and serotonin. Thus, the brain serotonin level depends on the TRP level in our body. The impropermetabolite of TRP causes hallucination, delusions, depression, Alzheimer’s and Parkinson’s diseases [5]. The present work aims to employ electrochemical method for the individual and simultaneous determination of LD and TRP at a new synthesized Fe3O4@Sio2-GO nanoparticles modified screen printed electrode. The modified electrode was used successfully as an electrochemical sensor for simultaneous determination of LD and TRP in real sample as a sensitive, selective, simple and rapid method. The linear dynamic range using this novel nano sensor for LD and TRP were 0.5-1000 and 1-1000 respectively.

Levodopa. Tryptophan. Fe3O4@Sio2-GO nanocomposite. Graphite screen-printedelectrodes