Printable graphene sensing systems for drug and alcohol detection.

Abstract

Over the past two decades, there has been a growing interest in monatomic and monomolecular sheets obtained through exfoliation of layered compounds. Despite this, none of these materials have opened the door to the design of more sensitive and reliable chemical sensors in the way that graphene has. Various properties of graphene such as high surface area, conductivity, flexibility, mechanical strength and most importantly the possibility of tuning its surface to develop new properties turned it into a great candidate to develop selective sensors, targeting chemical species that were previously difficult to detect. When developing sensors for alcohol and psychoactive drugs, the response time is an essential factor for many industrial, pharmaceutical and forensic applications, particularly when it comes to portable, point of care devices. The literature review begins the thesis by evaluating recent developments in sensing alcohol and drugs. The main focus of the thesis thereafter is the presentation of several newly created selective and sensitive detection techniques for drugs and alcohol, involving the use of 2D materials. Thesis discusses the strategies used to turn pristine graphene into a highly selective sensor and how reliable developed sensors are when testing various authentic samples such as drinks and human biological fluids. The surface-enhanced Raman spectroscopy (SERS) detection technique is also used to analyse and detect amitriptyline in dried saliva spots and dried blood spots. Some of the advantages of the developed sensors and methods in this project are their fast response, exceptional selectivity and significantly high sensitivity that can compete with methods such as gas chromatography – mass spectrometry techniques, yet offers affordability, simplicity of fabrication, ease of use, portability and elimination of sample pre-treatment steps. The first alcohol sensor, which was based on graphene and indium oxide, had a detection limit of 3.14×103 ppm and a linear range of 3.14×103 ppm to 5.53×104 ppm. In contrast, the second alcohol sensor, which was based on graphene and a new complex of indium ethylenediamine, exhibited a significantly improved detection limit of only 4.61 ppm and a broader linear range from 4.61 ppm to 1.38×105 ppm concentrations. Turning to drug sensing, a graphene-based amitriptyline electrochemical sensor was able to detect concentrations as low as 0.28 ppm, with a broad linear range between 0.28 ppm and 22.19 ppm. In comparison, the SERS sensor detected amitriptyline in blood and saliva, with a detection limit of 9.5×10-2 ppm and a linear range from 0.10 ppm to 1.75 ppm.