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.

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 μ A· μ M ⁻¹ ·cm ² ), limit of detection low (0.015 μ M), 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.

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 new electrode material of phosphorus-doped multi-walled carbon nanotubes (P-MWCNTs) was developed as an electrochemical sensing element for amitriptyline (AMT). P-MWCNTs were hydrothermally synthesized and drop casted on a glassy carbon electrode (P-MWCNTs/GCE). The P-MWCNTs were morphologically, chemically and structurally characterized. The electrochemical characteristics of the P-MWCNTs/GCE were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and adsorptive stripping voltammetry (AdSV). The P-MWCNTs increased electron transfer at the GCE and the electrochemical conductivity of the electrode. Electrocatalytic activity toward the oxidation of AMT was excellent. In the optimal voltammetric condition, the P-MWCNTs/GCE produced linear ranges of 0.50 to 10 μ g ml ⁻¹ and 10 to 40 μ g ml ⁻¹ . The limit of detection (LOD) and limit of quantification (LOQ) were 0.15 μ g ml ⁻¹ and 0.52 μ g ml ⁻¹ , respectively. The developed sensor displayed good repeatability, reproducibility and specificity. The sensor successfully quantified AMT in pharmaceutical tablets, giving results consistent with spectrophotometric analysis. The sensor achieved recoveries from 98 ± 2% to 101 ± 5% from spiked urine samples. The proposed sensor could be applied to determine AMT in pharmaceutical and urine samples for forensic toxicology.

Illicit methamphetamine is known to be the most manufactured amphetamine-type stimulants worldwide. Relatively simple manufacturing procedure had resulted in the creations of manufacturing sites in a variety of premises and structures, deserving forensic investigation. Therefore, this study was aimed to develop an electrochemical detection technique to determine the residual methamphetamine contamination on various surfaces. Carbon materials, namely graphene oxide, graphene nanoplatelets, graphene ink, and glassy carbon microsphere modified glassy carbon electrode were used in detecting methamphetamine by differential pulse voltammetry (DPV). The surface morphology modified electrode was characterised and its electrochemical behaviour was determined. Under optimal conditions, the calibration curve showed bilinear in the concentration range of 1−40 μ M and 40−120 μ M with good precision and accuracy. The limit of detection was determined to be 0.3 μ M. Graphene oxide modified electrode coupled with DPV successfully detected the residual methamphetamine on four household surfaces, including glass, stainless steel, plastic, and varnished wood with recoveries greater than 82%. To conclude, a novel electrochemical detection technique for the presence of methamphetamine was successfully developed to be applied in clandestine laboratory settings. It would be beneficial to assist the forensic investigation, especially for those forensic evidence recovered from suspicious and suspected clandestine laboratories.