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Tramadol (TRA) is a drug commonly used to alleviate severe pain. It is sometimes abused by teenagers, who mix it with beverages. A glassy carbon electrode (GCE) was modified with hierarchical graphene oxide nanoplatelets (H-GONPs) and proposed as an electrochemical sensor platform to detect TRA. The surface morphology of H-GONPs was compared with that of graphene oxide nanosheets (GONSs). Both materials were morphologically, chemically, and structurally characterized. The adsorption and determination of TRA at both electrodes were tested using electrical impedance spectroscopy, cyclic voltammetry, and adsorptive stripping voltammetry. The H-GONPs/GCE showed a faster charge transfer rate and larger active surface area. The anodic current response of TRA was three times higher at the H-GONPs/GCE than at the GONSs/GCE. In the optimal condition, the calibration curve of TRA demonstrated good linearity in two TRA concentration ranges. Electrode sensitivity was high (20.7 μA·μM−1·cm2), limit of detection low (0.015 μM), and precision and anti-interference good. The developed sensor was applied to detect TRA in pharmaceutical samples and spiked beverage, saliva, and urine samples. Recoveries were between 92 ± 4% and 102 ± 2% with RSDs < 4.3%. The results showed the good potential of the developed sensor for TRA detection.

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.