Abstract
The dissertation is on the development of electrochemical sensors for the detection of two
stimulants - caffeine and nicotine. These stimulants are well-known psychoactive central nervous
system drugs. Two different electrochemical sensors were prepared for caffeine and nicotine,
respectively, in this study.
The first electrochemical sensor was developed for the detection of caffeine using a carbon
nanofiber (CNF) modified glassy carbon electrode (GCE). Pristine CNF was treated with acid to
introduce new functional groups such as -C=O and -COOH. The pristine and acid treated CNF
were characterized by Fourier transform infrared spectroscopy and field emission scanning
electron microscopy, transmission electron microscopy, X-ray diffraction and Raman
spectroscopy. A solution of the acid treated CNF was prepared by dispersing 3 mg of CNF in 3
mL dimethylformamide (DMF) and sonicated for 30 min at 25 oC. The sensor was prepared by
drop coating a 5 μL volume of the dispersed CNF on a clean GCE followed by air drying at room
temperature and gentle rinsing with deionized water before use. The bare-GCE and CNF modified
GCE were characterized by voltammetry and electrochemical impedance spectroscopy (EIS). The
presence of CNF enhanced the electrochemical current response of the modified electrode. A
detection limit of 17.40 μM in the linear range of 25 – 450 μM of caffeine was achieved. The
sensor was selective in the presence of interferents such as glucose, acetaminophen and
acetylsalicylic acid. The sensor was used to analyze caffeine in real samples of pain relief tablets.
The method was validated with UV-vis spectrometry
An electrochemical sensor for nicotine (the second sensor) was prepared on a carbon
nanofiber/poly(amidoamine) dendrimer modified glassy carbon electrode. The carbon nanofiber
(CNF) modified glassy carbon electrode (GCE) was prepared by drop-coating followed by the
electrodeposition of generation 4 poly(amidoamine) succinamic acid dendrimer (PAMAM) to
form the sensor - CNF-PAMAM GCE. Characterization of prepared materials and modified
electrodes was carried out using Fourier transform infrared spectroscopy (FTIR), field emission
scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman
spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and differential
pulse voltammetry (DPV). The CNF-PAMAM demonstrated an enhanced performance in
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comparison to the bare GCE by shifting the anodic potential 𝐸𝑝𝑎 of nicotine from 0.9 V to 0.8 V
and showed an improved current response. A detection limit of 0.1646 μM in the concentration
range of 0.4815 to 15.41 μM of nicotine in 0.1 M PBS at pH 7.5 was obtained. Real samples
analysis of cigarettes at the CNF-PAMAM GCE obtained recovery percentage of 88.44 and 90.64
%, and the method was validated using UV-vis. Interference study in the presence of dopamine,
norepinephrine, glucose, KCl, citric acid, indicated that the sensor was able to produce a nicotine
peak in the presence of these chemicals and selectively produce the peaks of citric acid, glucose,
dopamine, and caffeine. The CNF modified GCE and CNF-PAMAM modified GCE showed good
reproducibility with relative standard deviation of % RSD 4.630 and 1.053 % respectively.