An innovative approach for selective and robust screening of NBOHs, NBOMes, and LSD in forensic samples using a 3D-Printed electrochemical double cell.

Lysergic acid diethylamide (LSD) and two phenethylamine classes (NBOHs and NBOMes) are the main illicit drugs found in seized blotter papers. The preliminary identification of these substances is of great interest for forensic analysis. In this context, this work constitutes the inaugural demonstration of an efficient methodology for the selective detection of LSD, NBOHs, and NBOMes, utilizing a fully 3D-printed electrochemical double cell (3D-EDC). This novel 3D-EDC enables the use of two working electrodes and/or two supporting electrolytes (at different pHs) in the same detection system, with the possibility of shared or individual auxiliary and pseudo-reference electrodes. Thus, the selective voltammetric detection of these substances is proposed using two elegant strategies: (i) utilizing the same 3D-EDC platform with two working electrodes (boron-doped diamond (BDD) and 3D-printed graphite), and (ii) employing two pH levels (4.0 and 12.0) with 3D-printed graphite electrode. This comprehensive framework facilitates a fast, robust, and uncomplicated electrochemical analysis. Moreover, this configuration enables a rapid and sensitive detection of LSD, NBOHs, and NBOMes in seized samples, and can also provide quantitative analysis. The proposed method showed good stability of the electrochemical response with RSD <9 % for Ip and <5 % for Ep, evaluating all oxidation processes observed for studied analytes (n = 7) at two pH levels, using the same and different (n = 3) working electrodes. It demonstrates a broad linear range (20-100 and 20-70 µmol L-1) and a low LOD (1.0 µmol L-1) for quantification of a model molecule (LSD) at the two pHs studied. Hence, the 3D-EDC combined with voltammetric techniques using BDD and 3D-printed graphite electrodes on the same platform, or only with this last sensor at two pH values, provide a practical and robust avenue for preliminary identification of NBOHs, NBOMes, and LSD. This method embodies ease, swiftness, cost-efficiency, robustness, and selectivity as an on-site screening tool for forensic analysis.

3D-printed electrodes using graphite/carbon nitride/polylactic acid composite material: A greener platform for detection of amaranth dye in food samples.

The production of sustainable materials with properties aimed at the additive manufacturing of electrochemical sensors has gained prestige in the scientific scenario. Here, a novel lab-made composite material using graphite (G) and carbon nitride (C3N4) embedded into polylactic acid (PLA) biopolymer is proposed to produce 3D-printed electrodes. PLA offers printability and mechanical stability in this composition, while G and C3N4 provide electrical properties and electrocatalytic sites, respectively. Characterizations by Raman and infrared spectroscopies and Energy Dispersive X-rays indicated that the G/C3N4/PLA composite was successfully obtained, while electron microscopy images revealed non-homogeneous rough surfaces. Better electrochemical properties were achieved when the G/C3N4/PLA proportion (35:5:60) was used. As a proof of concept, amaranth (AMR), a synthetic dye, was selected as an analyte, and a fast method using square wave voltammetry was developed. Utilizing the 3D-printed G/C3N4/PLA electrode, a more comprehensive linear range (0.2 to 4.2 µmol/L), a 5-fold increase in sensitivity (9.83 µmol-1 L µA), and better limits of detection (LOD = 0.06 µmol/L) and quantification (LOQ = 0.18 µmol/L) were achieved compared to the G/PLA electrode. Samples of jelly, popsicles, isotonic drinks, and food flavoring samples were analyzed, and similar results to those obtained by UV-vis spectrometry confirmed the method's reliability. Therefore, the described sensor is a simple, cost-effective alternative for assessing AMR in routine food analysis.

Novel disposable and portable 3D-printed electrochemical apparatus for fast and selective screening of 25E-NBOH in forensic samples.

The advent of new psychoactive substances (NPS) has caused enormous difficulty for legal control since they are rapidly commercialized, and their chemical structures are routinely altered. In this aspect, derivatives phenethylamines, such as 25E-NBOH, have received great attention in the forensic scenario. Hence, we propose portable and cost-effective (U$ 5.00) 3D-printed devices for the electrochemical screening of 25E-NBOH for the first time. The cell and all electrodes were printed using acrylonitrile butadiene styrene filament (insulating material) and conductive filament (graphite embedded in a polylactic acid matrix), respectively, both by the fused deposition modeling (FDM) 3D printing technique. The electrochemical apparatus enables micro-volume analysis (50-2000 µL), especially important for low sample volumes. A mechanistic route for the electrochemical oxidation of 25E-NBOH is proposed based on cyclic voltammetric data, which showed two oxidation processes around +0.75 V and +1.00 V and a redox pair between +0.2 and -0.2 V (vs. graphite ink pseudo-reference). A fast and sensitive square-wave voltammetry method was developed, which exhibited a linear working range from 0.85 to 5.1 µmoL-1, detection limit of 0.2 µmol L-1, and good intra-electrode precision (n = 10, RSD <5.3 %). Inter-electrode measurements (n = 3, RSD <9.8 %) also attested that the electrode production process is reproducible. Interference tests in the presence of other drugs frequently found in blotting paper indicated high selectivity of the electrochemical method for screening of 25E-NBOH. Screening analysis of blotting paper confirmed the presence of 25E-NBOH in the seized samples. Moreover, a recovery percentage close to 100 % was found for a spiked saliva sample, suggesting the method's usefulness for quantitative purposes aimed at information on recent drug use.

A novel 3D-printed graphite/polylactic acid sensor for the electrochemical determination of 2,4,6-trinitrotoluene residues in environmental waters.

Here, lab-made graphite and polylactic acid (Gpt-PLA) biocomposite materials were used to additively manufacture electrodes via the fused deposition modeling (FDM) technique for subsequent determination of the explosive 2,4,6-trinitrotoluene (TNT, considered a persistent organic pollutant). The surface of the 3D-printed material was characterized by SEM and Raman, which revealed high roughness and the presence of defects in the graphite structure, which enhanced the electrochemical response of TNT. The 3D-printed Gpt-PLA electrode coupled to square wave voltammetry (SWV) showed suitable performance for fastly determining the explosive residues (around 7 s). Two reduction processes at around -0.22 V and -0.36 V were selected for TNT detection, with linear ranges between 1.0 and 10.0 µM. Moreover, detection limits of 0.52 and 0.66 µM were achieved for both reduction steps. The proposed method was applied to determine TNT in different environmental water samples (tap water, river water, and seawater) without a dilution step (direct analysis). Recovery values between 98 and 106% confirmed the accuracy of the analyses. Additionally, adequate selectivity was achieved even in the presence of other explosives commonly used by military agencies, metallic ions commonly found in water, and also some electroactive camouflage species. Such results indicate that the proposed device is promising to quantify TNT residues in environmental samples, a viable on-site analysis strategy.

3D printed graphite-based electrode coupled with batch injection analysis: An affordable high-throughput strategy for atorvastatin determination.

This work integrated a lab-made conductive graphite/polylactic acid (Grp/PLA, 40:60% w/w) filament into a 3D pen to print customized electrodes (cylindrical design). Thermogravimetric analysis validated the incorporation of graphite into the PLA matrix, while Raman spectroscopy and scanning electron microscopy images indicated a graphitic structure with the presence of defects and highly porous, respectively. The electrochemical features of the 3D-printed Gpt/PLA electrode were systematically compared to that achieved using commercial carbon black/polylactic acid (CB/PLA, from Protopasta®) filament. The 3D printed Gpt/PLA electrode "in the native form" provided lower charge transfer resistance (Rct = 880 Ω) and a more kinetically favored reaction (K0 = 1.48 × 10-3 cm s-1) compared to the 3D printed CB/PLA electrode (chemically/electrochemically treated). Moreover, a method by batch injection analysis with amperometric detection (BIA-AD) was developed to determine atorvastatin (ATR) in pharmaceutical and water samples. Using the 3D printed Gpt/PLA electrode, a wider linear range (1-200 µmol L-1), sensitivity (3-times higher), and lower detection limit (LOD = 0.13 µmol L-1) were achieved when compared to the CB/PLA electrode. Repeatability studies (n = 15, RSD <7.3%) attested to the precision of the electrochemical measurements, and recovery percentages between 83 and 108% confirmed the accuracy of the method. Remarkably, this is the first time that ATR has been determined by the BIA-AD system and a low-cost 3D-printed device. This approach is promising to be implemented in research laboratories for quality control of pharmaceuticals and can also be useful for on-site environmental analysis.

Electrochemical platform produced by 3D printing for analysis of small volumes using different electrode materials.

Fused deposition modeling (FDM) 3D printing is a promising additive manufacturing technique to produce low-cost disposable electrochemical devices. However, the print of devices like well-known screen-printed electrodes (all electrodes on the same device) is difficult using the available technology (few materials available for production of working electrodes). In this paper we present a procedure to produce disposable and robust electrochemical devices by FDM 3D printing that allows reproducible analysis of small volumes (50-2000 µL). The device consists of just two printed parts that allow easy coupling of different conductive materials for using as disposable or non-disposable working electrodes with reproducible geometric area. Printed counter and pseudo-reference electrodes can also be easily fitted into the microcell. Moreover, conventional counter (platinum wire) and mini reference electrodes can also be used. As a proof of concept, paracetamol, cocaine and uric acid were used as model analytes using different materials as working electrodes. Linear calibration curves (r > 0.99) with similar slopes (0.29 ± 0.01 µA µmol L-1; RSD = 3.4%) were obtained by square wave voltammetry (SWV) using a complete printed system and different volumes of standard solutions of paracetamol (50, 100, and 200 µL). For uric acid, a linear range of 10-125 µmol L-1 (r > 0.99), was obtained using differential pulse voltammetry as the electrochemical technique and a disposable laser-induced graphene base as the working electrode. With the coupling of boron-doped diamond working electrode, screening tests were successfully performed in seized cocaine samples with selective detection of cocaine in the presence of its most common adulterants. The production cost per unit of a complete electrochemical system is around US 5.00. In large-scale production, only the working electrode needs to be replaced while the microcell and counter/pseudo reference electrodes do not need to be discarded.

Lab-made 3D-printed electrochemical sensors for tetracycline determination.

Antibiotics such as tetracycline (TC) are widely prescribed to treat humans or dairy animals. Therefore, it is important to establish affordable devices in laboratories with minimal infrastructure. 3D printing has proven to be a powerful and cost-effective tool that revolutionizes many applications in electrochemical sensing. In this work, we employ a conductive filament based on graphite (Gr) and polylactic acid (PLA) (40:60; w/w; synthesized in our lab) to manufacture 3D-printed electrodes. This electrode was used "as printed" and coupled to batch injection analysis with amperometric detection (BIA-AD) for TC sensing. Preliminary studies by cyclic voltammetry and differential pulse voltammetry revealed a mass transport governed by adsorption of the species and consequent fouling of the redox products on the 3D printed surface. Thus, a simple strategy (solution stirring and application of successive potentials, +0.95 V followed by +1.2 V) was associated with the BIA-AD system to solve this effect. The proposed electrode showed analytical performance comparable to costly conventional electrodes with linear response ranging from 0.5 to 50 µmol L-1 and a detection limit of 0.19 µmol L-1. Additionally, the developed method was applied to pharmaceutical, tap water, and milk samples, which required minimal sample preparation (simple dilution). Recovery values of 92-117% were obtained for tap water and milk samples, while the content found of TC in the capsule was close to the value reported by the manufacturer. These results indicate the feasibility of the method for routine analysis involving environmental, pharmaceutical, and food samples.

Carbon Black Integrated Polylactic Acid Electrodes Obtained by Fused Deposition Modeling: A Powerful Tool for Sensing of Sulfanilamide Residues in Honey Samples.

Sulfanilamide (SFL) is used to prevent infections in honeybees. However, many regulatory agencies prohibit or establish maximum levels of SFL residues in honey samples. Hence, we developed a low-cost and portable electrochemical method for SFL detection using a disposable device produced through 3D printing technology. In the proposed approach, the working electrode was printed using a conductive filament based on carbon black and polylactic acid and it was associated with square wave voltammetry (SWV). Under optimized SWV parameters, linear concentration ranges (1-10 µmol L-1 and 12.5-35.0 µmol L-1), a detection limit of 0.26 µmol L-1 (0.05 mg L-1), and suitable RSD values (2.4% for inter-electrode; n = 3) were achieved. The developed method was selective in relation to other antibiotics applied in honey samples, requiring only dilution in the electrolyte. The recovery values (85-120%) obtained by SWV were statistically similar (95% confidence level) to those obtained by HPLC, attesting to the accuracy of the analysis and the absence of matrix interference.

Sensing performances of spinel ferrites MFe2O4 (M = Mg, Ni, Co, Mn, Cu and Zn) based electrochemical sensors: A review.

The history of ferrites comes from many centuries and was fundamental in many fields. Initially, ferrites were extracted directly from nature, but in the last century, scientists learned to produce ferrites with different properties that gave origin to many advances in industrial and instrumental applications. More recently, the designed preparation of ferrites with nanometric size revealed remarkable characteristics. In the last years, different spinel ferrites were used as electroactive layers to build high-performance modified electrodes. In this review, it is presented a critical overview of the utilization of spinel ferrites (with a general formula MFe2O4, where M2+ = Mg2+, Ni2+, Co2+, Cu2+, Mn2+ and Zn2+) to create differentiated voltammetric sensors. The association of these materials with graphene, glassy carbon, carbon nitride, ionic liquids, nanoparticles of noble metals, oxides of transition metals and other materials can produce notable synergic responses towards electrochemical activity. Some of these sensors can produce very sensitive signals and ample concentration ranges for compounds such hydrogen peroxide, glucose and bisphenol A, and present potential for many other applications. Along this review, all these aspects will be discussed and the main results are organized in tables, using as a base the metal associated with the ferrite.

Additively manufactured electrodes for the electrochemical detection of hydroxychloroquine.

Although studies have demonstrated the inactivity of hydroxychloroquine (HCQ) towards SARS-CoV-2, this compound was one of the most prescribed by medical organizations for the treatment of hospitalized patients during the coronavirus pandemic. As a result of it, HCQ has been considered as a potential emerging contaminant in aquatic environments. In this context, we propose a complete electrochemical device comprising cell and working electrode fabricated by the additive manufacture (3D-printing) technology for HCQ monitoring. For this, a 3D-printed working electrode made of a conductive PLA containing carbon black assembled in a 3D-printed cell was associated with square wave voltammetry (SWV) for the fast and sensitive determination of HCQ. After a simple surface activation procedure, the proposed 3D-printed sensor showed a linear response towards HCQ detection (0.4-7.5 µmol L-1) with a limit of detection of 0.04 µmol L-1 and precision of 2.4% (n = 10). The applicability of this device was shown to the analysis of pharmaceutical and water samples. Recovery values between 99 and 112% were achieved for tap water samples and, in addition, the obtained concentration values for pharmaceutical tablets agreed with the values obtained by spectrophotometry (UV region) at a 95% confidence level. The proposed device combined with portable instrumentation is promising for on-site HCQ detection.

Prussian blue-modified laser-induced graphene platforms for detection of hydrogen peroxide.

A laser-induced graphene (LIG) surface modified with Prussian blue (iron hexacyanoferrate) is demonstrated as a novel electrochemical sensing platform for the sensitive and selective detection of hydrogen peroxide. Electrochemical Prussian blue (PB) modification on porous graphene films engraved by infrared laser over flexible polyimide was accomplished. Scanning electron microscopy images combined with Raman spectra confirm the formation of porous graphene and homogenous electrodeposition of PB over this porous surface. Electrochemical impedance spectroscopy reveals a substantial decrease in the resistance to charge transfer values (from 395 to 31.4 Ω) after the PB insertion, which confirms the formation of a highly conductive PB-graphene composite. The synergistic properties of PB and porous graphene were investigated for the constant monitoring of hydrogen peroxide at 0.0 V vs. Ag|AgCl|KCl(sat.), under high-flow injections (166 µL s-1) confirming the high stability of the modified surface and fast response within a wide linear range (from 1 to 200 µmol L-1). Satisfactory detection limit (0.26 µmol L-1) and selectivity verified by the analysis of complex samples confirmed the excellent sensing performance of this platform. We highlight that the outstanding sensing characteristics of the developed sensor were superior in comparison with other PB-based or LIG-based electrochemical sensors reported for hydrogen peroxide detection.

Affordable equipment to fabricate laser-induced graphene electrodes for portable electrochemical sensing.

Graphene-based materials present unique properties for electrochemical applications, and laser-induced conversion of polyimide to graphene is an emerging route to obtain a high-quality material for sensing. Herein we present compact and low-cost equipment constructed from an open-source 3D printer at which a 3.5-W visible (449 nm) laser was adapted to fabricate laser-induced graphene (LIG) electrodes from commercial polyimide, which resulted in electron transfer kinetic (k0) of 5.6 × 10-3 cm s-1 and reproducibility calculated by relative standard deviation (RSD < 5%) from cyclic voltammograms of [Fe(CN)6]3-/4- using 5 different electrodes. LIG electrodes enabled the simultaneous voltammetric determination of uric acid (+ 0.1 V vs. pseudo-reference) and nitrite (+ 0.4 V vs pseudo-reference), with limit of detection (LOD) values of 0.07 and 0.27 µmol L-1, respectively. Amperometric measurements for the detection of H2O2 (applying + 0.0 V vs. Ag|AgCl|KCl(sat.)) after Prussian blue (PB) modification and ciprofloxacin (applying + 1.2 V vs. Ag|AgCl|KCl(sat.)) were performed under flow conditions, which confirmed the high stability of LIG and LIG-PB surfaces. The LOD values were 1.0 and 0.2 µmol L-1 for H2O2 and ciprofloxacin, respectively. The RSD values (< 12%) obtained for the analysis using three different electrodes attested the precision of LIG electrodes manufactured in two designs. No sample matrix effects on the determination of ciprofloxacin in milk samples were observed  (recoveries between 84 and 96%). The equipment can be built with less than $300 and each LIG electrode costs less than $0.01.

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.

Acanthamoeba castellanii as an alternative interaction model for the dermatophyte Trichophyton rubrum.

BACKGROUND: Trichophyton rubrum (Tr) is the main aetiological agent of human dermatophytosis, being isolated from the environment and keratinised tissues. In the environment, Tr can interact with other organisms, such as free-living amoebas (FLA), which can act as an alternative host system to study the interaction between microbes and phagocytic cells. OBJECTIVES: To characterise the Acanthamoeba castellanii (ALX)-Tr interaction. METHODS: Interaction was characterised in three conditions: trophozoites (PYG), late (PYG/NES) and early (NES) encystation stimulus, evaluating encystation kinetics, phagocytosis, exocytosis and fungicidal activity dynamics. RESULTS: Tr was able to induce ALX encystation and be internalised by ALX. The number of internalised conidia was high at 1 hour, and ALX presented fungicidal activity with increased intracellular ROS production and exocytosis. In PYG/NES, phagocytosis and ROS production were reduced, with decreased ALX's fungicidal activity. However, in NES there was an increased fungal engulfment, and a reduced ROS production and higher fungal burden. Furthermore, exogenous mannose decreased phagocytosis of Tr conidia, and divalent cations induced ROS production and increased ALX's fungicidal activity. Interestingly, phagocytosis was reduced in the presence of cytoskeleton inhibitor, but exocytosis was increased, suggesting that Tr conidia may have alternative pathways to escape ALX's cells. CONCLUSION: A castellanii is a proper model for studying Tr-FLA interaction, since ALX can engulf, produce ROS and kill Tr, and all these parameters are influenced by an encystation stimulus and divalent cations. Moreover, this interaction is likely to occur in the environment implicating in the adaptation to environmental stressful conditions in both organisms.