Detecting Methamphetamine with Organic Electrochemical Transistor (OECT)

Methamphetamine, well-known as a highly addictive CNS stimulant, has been involved into an overdose crisis in US in recent years. According to National Institute on Drug Abuse (NIDA), since 2015 to 2019, the methamphetamine-related overdose deaths nearly tripled. National Forensic Laboratory Information System (NFLIS)-drug 2020 midyear Report¹ highlighted methamphetamine was still the most frequently identified drug, which indicates the critical need for rapid detection of methamphetamine in a way that is simple, low-cost, and robust enough for high throughput forensic analysis.<br/>Organic Electrochemical Transistors (OECTs) have drawn considerable attention as the potential sensors in recent decades due to its capability of amplifying the tiny voltage variation on the gate electrode into the enhanced drain current. Typically, an OECT device consists of three electrodes where source and drain electrodes are connected by a semiconductor channel comprised of a conjugated polymer and an electrolyte which separates the semiconducting polymer and the gate electrode. OECTs work by doping/dedoping the organic semiconducting channel via applying an appropriate gate voltage. Hence the injected ions will penetrate the semiconducting film to regulate the number of charge carriers between the source and drain electrodes. The detection limit of OECT device can reach as low as picomolar level.² Moreover, OECT operates at low working voltages (&lt; 1 V) and can provide the direct contact between the electrolyte solution and the semiconducting polymer, which is especially compatible with biological systems. Both mentioned attributes render the use of OECTs as biosensors³ for detecting ions, metabolites, enzymes, neurotransmitters, glucose, DNA, etc. Furthermore, the capability of examining both inorganic⁴ and organic⁵ analytes with OECTs is especially impressive, allowing the alternative means to investigate forensic toxicological samples. Finally, compared to other instruments often implemented in forensic analysis, OECTs present the cost-effectiveness and more importantly, the versatility of design, making them suitable for inspecting all kind of physical evidences such as drugs, biological specimens, explosives, gunshot residues, fire accelerants, warfare agents etc. However, scarce reports regarding the forensic applications with OECTs are in the literature so far.<br/>In this work, an OECT device was successfully fabricated with the thermally crosslinked 1:1 (v/v) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) as the semiconductor channel and a phosphate-buffered saline (PBS) solution with 0.1 M KCl as the electrolyte. The resulting output and transfer <i>I</i>-<i>V</i> curves demonstrate that the established device exhibits classic OECT behaviors. Furthermore, to increase the specificity of the OECT for detecting methamphetamine, a molecularly imprinted polymer (MIP) was created on the gate electrode and the initial exploration for detecting the presence of methamphetamine in a PBS buffer, manifested promising sensitivity at ppm level.<br/><b>References</b><br/>(1) <i>NFLIS-DRUG 2020 MIDYEAR REPORT</i>: U.S. Department of Justice, Drug Enforcement Administration, <b>2020</b>.<br/>(2) Lin, P.; Luo, X.; Hsing, I. M.; Yan, F. Organic electrochemical transistors integrated in flexible microfluidic systems and used for label-free DNA sensing. <i>Adv. Mater.</i> <b>2011</b>, <i>23</i>, 4035.<br/>(3) Sophocleous, M.; Contat-Rodrigo, L.; Garcia-Breijo, E.; Georgiou, J. Organic Electrochemical Transistors as an Emerging Platform for Bio-Sensing Applications: A Review. <i>IEEE Sens. J.</i> <b>2021</b>, <i>21</i>, 3977-4006.<br/>(4) Sessolo, M.; Rivnay, J.; Bandiello, E.; Malliaras, G. G.; Bolink, H. J. Ion-selective organic electrochemical transistors. <i>Adv. Mater.</i> <b>2014</b>, <i>26</i>, 4803.<br/>(5) D'Angelo, P.; Tarabella, G.; Romeo, A.; Marasso, S. L.; Cocuzza, M.; Peruzzi, C.; Vurro, D.; Carotenuto, G.; Iannotta, S. Nanomolar detection of the antitumor drug tamoxifen by flexible organic electrochemical devices. <i>AIP Conf. Proc.</i> <b>2018</b>, <i>1990</i>, 020015.