Lab-made CO2 laser-engraved electrochemical sensors for ivermectin determination.

The ivermectin (IVM), as a broad-spectrum antiparasitic drug, was widely prescribed to treat COVID-19 during the pandemic, despite lacking proven efficacy in combating this disease. Therefore, it is important to establish affordable devices in laboratories with minimal infrastructure. The laser engraving technology has been revolutionary in sensor manufacturing, primarily attributed to the diversity of substrates that can be employed and the freedom it provides in creating sensor models. In this work, electrochemical sensors based on graphene were developed using the laser engraving technology for IVM sensing. Through, the studies that used the techniques of cyclic voltammetry and differential pulse voltammetry, following parameter optimization, for the laser-induced graphene electrode demonstrated a mass transport governed by adsorption of the species and exhibited a linear working range of 10-100 (µmol L-1), a limit of detection (LOD) of 1.6 × 10-6 (mol L-1), a limit of quantification (LOQ) of 4.8 × 10-6 (mol L-1), and a sensitivity of 0.139 (µA µmol L-1). The developed method was successfully applied to direct analysis of pharmaceutical tablets, tap water (recovery of 94%) and synthetic urine samples (recovery between 97% and 113%). These results demonstrate the feasibility of the method for routine analyses involving environmental samples.

Electrochemical determination of several biofuel antioxidants in biodiesel and biokerosene using polylactic acid loaded with carbon black within 3D-printed devices.

Low oxidation stability is the main drawback of biodiesels and biokerosenes that is overcome by using antioxidants, which can be combined due to synergistic effects. This paper demonstrates that 3D-printed electrochemical devices can be applied to biofuel electroanalysis, including the monitoring of oxidation stability by quantifying the antioxidant content in biofuels. Fabrication requires 3D-printed acrylic templates at which a polylactic acid (PLA) filament with conducting carbon-black filling sensors is extruded by a 3D pen. The antioxidants butyl hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ) are the most employed additives in biodiesel production, and thus, their electrochemical behavior was investigated; 2,6-ditertbutylphenol (2,6-DTBP) was included in this investigation because it is commonly added to biokerosenes. The electrochemical surface treatment of the 3D-printed electrodes improved the current responses of all antioxidants; however, the electrochemical oxidation of TBHQ was clearly more affected by an electrocatalytic action shifting its oxidation towards less positive potentials (~200 mV), which resulted in a better separation of TBHQ and BHA oxidation peaks (+0.4 and +0.6 V vs Ag|AgCl, respectively). The oxidation of 2,6-DTBP occurred at more positive potentials (+1.2 V vs Ag|AgCl). The simultaneous determination of TBHQ and BHA by differential-pulse voltammetry resulted in linear responses in the range 0.5 and 175 µmol L-1 with limits of detection and quantification of 0.15 µmol L-1 and 0.5 µmol L-1, respectively. The presence of Fe3+, Cu2+, Pb2+, Mn2+, Cd2+, and Zn2+, even in high concentrations, did not interfere in the determination of TBHQ and BHA. The determination of 2,6-DTBP in biokerosene was achieved by cyclic voltammetry. All relative standard deviations (RSD) were lower than 6.0 %, indicating adequate precision of the methods. Spiked biofuel samples were analyzed (after dilution in electrolyte) and recovery values between 85 and 120% were obtained, which indicates absence of sample matrix effects.