In
this study, we have designed and fabricated a portable electrochemical
sensor for direct detection of capsaicin in chili samples at the point-of-testing.
The sensor, shaped like a chili pepper and highly portable, is essentially
a disposable electrochemical paper-based analytical device (ePAD)
modified with N-doped graphene nanoplatelets (GrNPs). The sensor consists
of three components: (i) a small potentiostat device, (ii) an interface
allowing connection to a smartphone for monitoring and control, and
(iii) the sensor (an N-doped GrNPs/ePAD and detection chamber). The
N-doped GrNPs/ePAD shows high conductivity and good electrocatalytic
activity in the oxidation and reduction of capsaicin. The measurement
of capsaicin was performed directly through differential pulse voltammetry
once the parameters influencing capsaicin detection (i.e., pH, buffer
ethanol content, N-doped GrNPs loading, accumulation potential, and
accumulation time) were optimized. Linearity was obtained in the concentration
range 1–100 μM, and the limit of detection was found
to be 0.37 μM. Furthermore, the preparation of ten N-doped GrNPs/ePAD
devices confirmed fabrication reproducibility. The sensor was successfully
applied to the determination of capsaicin in chili samples, with recoveries
between 89.3 ± 0.3 and 106 ± 2%, and the results showed
no significant difference to those obtained by UV–vis spectrophotometry.
Thus, this platform shows excellent potential for the development
of portable sensors for capsaicin and future extension to different
analytes.
Overdose of atropine usually leads to heart failure and death and has long been used as a method of murder. We propose a simple electrochemical approach for atropine sensing using an electrode modified with nafion/polycarboxylate functionalized graphene nanoflakes (Nf/p-GNF/E). The polycarboxylate functionalized graphene nanoflakes were characterized by SEM, FT-IR, and electrochemical techniques. The electrochemical behavior and determination of atropine at the Nf/p-GNF/E were examined using cyclic voltammetry (CV) and adsorptive anodic stripping voltammetry (AdASV). The amount of Nf/p-GNF drop-cast on the electrode, accumulation potential and time, and pH buffer were optimized. Under the optimized conditions, the modified electrode showed excellent electrochemical oxidation of atropine with a linear range from 6.0 × 10−6 to 1.0 × 10−4 mol L−1 and a detection limit of 1.9 × 10−6 mol L−1. The proposed sensor exhibited excellent repeatability (RSD < 2.8%), reproducibility (RSD < 2.7%), and good resistance to interference from glucose, fructose, dopamine, uric acid, and ascorbic acid. The sensor was applied to determine atropine in urine samples and the results were in good agreement with results from the spectrophotometric analysis.
A 3D porous graphene structure was directly induced by CO2 laser from the surface of Kapton tape (carbon source) supported by polyethylene terephthalate (PET) laminating film. A highly flexible laser-induced porous graphene (LI-PGr) electrode was then fabricated via a facile one-step method without reagent and solvent in a procedure that required no stencil mask. The method makes pattern design easy, and production cost-effective and scalable. We investigated the performance of the LI-PGr electrode for the detection of methamphetamine (MA) on household surfaces and in biological fluids. The material properties and morphology of LI-PGr were analysed by scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and Raman spectroscopy. The LI-PGr electrode was used as the detector in a portable electrochemical sensor, which exhibited a linear range from 1.00 to 30.0 µg mL−1 and a detection limit of 0.31 µg mL−1. Reproducibility was good (relative standard deviation of 2.50% at 10.0 µg mL−1; n = 10) and anti-interference was excellent. The sensor showed good precision and successfully determined MA on household surfaces and in saliva samples.
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