Aminoxyl Catalyzed Electrochemical Ethanol Detection: Development of a New Breathalyzer Using Molecular Catalysis

Abstract

Blood alcohol concentration (BAC) is the indicator of alcohol intoxication, and its measurement has emerged as the most common analytical procedure requested by law enforcement. Due to its volatility, ethanol vapor can be detected in breath, and its vapor concentration is proportional to BAC. Currently available instrumentation used for breath alcohol content (BrAC) analysis include gas chromatography (GC) and GC coupled with mass spectrometry, infrared (IR) spectroscopy, and fuel cell based electrochemical sensors. GC and IR spectroscopy devices have some drawbacks such as size, initial cost, and operational expense. Electrochemical sensors are capable of miniaturization and are available as portable and handheld breathalyzers. However, the lack of a single use and disposable sensing element, resulting memory effect and the need for frequent recalibration is the main drawback of currently available electrochemical breathalyzers. There have been few attempts at designing a sensing element to improve the current methods of alcohol detection by electrochemical techniques, all relying on enzymatic alcohol oxidation.1 Herein, we report a proof-of-concept non-enzymatic breathalyzer, harnessing the unique catalytic activity of the aminoxyl radical/oxoammonium redox couple toward alcohol oxidation.2 The relatively low redox potentials of aminoxyls, the mild conditions required for use, and their selective interactions with ethanol are their advantages compared to currently available Pt based breathalyzers. Our functional sensing element consists of a screen-printed electrode in which the graphene oxide-based working electrode is modified with aminoxyl derivatives, of which 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl benzoate (TMB) was the most efficient derivative. Exposing this modified electrode to simulated breath that contains ethanol, while applying the required potential for oxidation of the aminoxyl radical, generates an electrocatalytic current proportional to the ethanol concentration in the breath. These simple, sensitive, durable, and inexpensive electrodes may contribute to the development of a single-use reliable ethanol sensor for personal or law enforcement applications. Heikenfeld, J.; Jajack, A.; Rogers, J.; Gutruf, P.; Tian, L.; Pan, T.; Li, R.; Khine, M.; Kim, J.; Wang, J.; Kim, J. Wearable Sensors: Modalities, Challenges, and Prospects. Lab Chip 2018, 18, 217. Nutting, J. E.; Rafiee, M.; Stahl, S. S. Tetramethylpiperidine N-Oxyl (TEMPO), Phthalimide N-Oxyl (PINO), and Related N-Oxyl Species: Electrochemical Properties and Their Use in Electrocatalytic Reactions. Chem. Rev. 2018, 118, 4834.