Oxygen plasma-treated graphite sheet electrodes: A sensitive and disposable sensor for methamphetamines

3,4-methylenedioxymethamphetamine (MDMA) is a drug of abuse, known as ecstasy, and it is among the most consumed drugs worldwide. The presence of MDMA and new psychoactive substances has been widely reported in seized forensic samples. The development of an elective and sensitive screening method for MDMA detection is very important in the current scenario of illicit drugs. In this paper, we present affordable graphite sheet (GS) electrodes a new sensing platform for MDMA detection. Importantly, a surface treatment protocol for these electrodes using cold plasma improves the electrochemical response of MDMA. The XPS results showed that O2 plasma treatment changed the GS electrode surface, creating oxide groups. GSs were characterized before and after treatment by scanning electron microscopy and electrochemical impedance spectroscopy, and the results suggested a higher surface area and lower resistance to the charge transfer for treated GS electrodes. Using differential pulse voltammetry, it was possible to achieve a linear range from 0.5 to 15.0 mu mol L-1 with a low limit of detection (0.09 mu mol L-1). Higher interaction of MDMA with the plasma-treated GS surface (in comparison with the pristine surface) was confirmed by computational simulations (molecular dynamics), which may explain the improved sensing properties provided by the plasma treatment. Additionally, the interference study with other drugs usually found in seized ecstasy tablets showed high selectivity which enabled MDMA detection in human saliva (collected in parties and electronic music festivals) and seized samples. Therefore, plasma treated GS can be used as a simple, fast, low-cost, and portable screening device for application in real-world forensic samples.