Abstract
To address the concerns about the neurotoxicity of nicotine in flavoured hookah pipe tobacco and other adverse health effects, we developed electrochemical sensors for detecting nicotine and dopamine. Exposure to high concentrations of nicotine causes the brain cells to release more dopamine than normal, leading to imbalances that can result to chronic mental and neurological illnesses. Since nicotine is addictive, these illnesses can permanently affect individual’s social lives and career progression. Therefore, it is crucial for hookah pipe tobacco product users, whether recreationally or for medical purposes, to be aware of the nicotine content they are consuming and the associated health risks.
This research focuses on developing electrochemical sensors for detecting nicotine, the addictive substance in hookahs, and dopamine, the neurotransmitter directly linked to addiction and mental//neurological health impairments. Electrochemical sensors are simpler, more sensitive, cost-effective, and robust than conventional methods for quantifying analytes like nicotine and dopamine, especially when modified with nanomaterials. Using nanocomposites of carbon nanomaterials, a conductive polymer, and a dendrimer, we enhanced the electrocatalytic properties and conductivity of the glassy carbon electrode (GCE), improving its fouling resistance, selectivity, and sensitivity for nicotine and dopamine detection. Before application, the nanomaterials were characterized using field emission electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, to study their physicochemical properties.
The first sensor was developed by drop-casting synthesised nitrogen-doped carbon nanosheets (N-CNS) onto the bare GCE, followed by electrodeposition of commercial generation 4 poly(amidoamine)-succinamic acid (PAMAM-G4-SAH) dendrimer. The GCE’s electrocatalytical performance was assessed before and after each modification step using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) in 5mM ferry/ferrocyanide, and differential pulse voltammetry (DPV) in 0.96 μM nicotine. The nanocomposite sensor (GCE/N-CNS/PAMAM) detected nicotine in standard samples, in the linear concentration range of 0-64 μM nicotine in 10 mM phosphate buffer saline (PBS, pH 7.45) solution, achieving a detection limit of 0.05 μM. The sensor was then applied in two brands of flavoured hookah pipe tobacco extracts, recovering 113-121 % nicotine. The detected
viii
amount of 0.35-0.39 mg/g nicotine suggests possible harm to human health, especially considering that individuals use 15-20 g hookah flavour per session.
The second sensor was developed by drop coating commercial graphene-poly(ethylenedioxythiophene): polystyrene sulphonate (Gr-PEDOT: PSS) hybrid ink onto the bare GCE. The bare and modified GCEs were also characterised using CV and EIS in 5 mM ferri/ferrocyanide and 50 μM dopamine to study the conductive properties of the modifier. The nanocomposite sensor (GCE/Gr-PEDOT: PSS) demonstrated high sensitivity and selectivity when tested in the dopamine concentration range of 0-400 μM, and in the presence of other analytes, achieving the detection limit of 0.19 μM. When applied in human serum, the sensor achieved recoveries of 105-109 %. The results from both sensors were verified using ultraviolet-visible (UV-Vis) spectroscopy. Both sensors are repeatable and reproducible, making them suitable for application in clinical samples of flavoured hookah pipe tobacco smokers.