Simultaneous monitoring of amoxicillin and paracetamol in synthetic biological fluids using a 3D printed disposable electrode with a lab-made conductive filament.

In this work, we are pleased to present for the first time a 3D-printed electrochemical device using a lab-made conductive filament based on graphite (Gr) and polylactic acid (PLA) polymer matrix for the simultaneous detection of amoxicillin (AMX) and paracetamol (PAR). The sensor was properly characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Compared to the commercial glassy carbon electrode (GCE), the superior performance of the 3D-Gr/PLA electrode was verified with a 3.8-fold more favored charge transfer. A differential pulse voltammetry (DPV) method was proposed providing a linear working range of 4 to 12 µmol L-1 for both analytes and a limit of detection (LOD) of 0.80 and 0.51 µmol L-1 for AMX and PAR, respectively. Additionally, repeatability studies (n = 5, RSD < 5.7%) indicated excellent precision, and recovery percentages ranging from 89 to 109% when applied to synthetic human urine, saliva, and plasma samples, attested to the accuracy of the method. The studies also indicate that the sensor does not suffer significant interference from common substances (antibiotics and biomarkers) present in the biological fluids, which makes it a promising analytical tool considering its low-cost, ease of manufacturing, robustness, and electrochemical performance.

Cost-effective protocol to produce 3D-printed electrochemical devices using a 3D pen and lab-made filaments to ciprofloxacin sensing.

A novel conductive filament based on graphite (Gr) dispersed in polylactic acid polymer matrix (PLA) is described to produce 3D-electrochemical devices (Gr/PLA). This conductive filament was used to additively manufacture electrochemical sensors using the 3D pen. Thermogravimetric analysis confirmed that Gr was successfully incorporated into PLA, achieving a composite material (40:60% w/w, Gr and PLA, respectively), while Raman and scanning electron microscopy revealed the presence of defects and a high porosity on the electrode surface, which contributes to improved electrochemical performance. The 3D-printed Gr/PLA electrode provided a more favorable charge transfer (335 Ω) than the conventional glassy carbon (1277 Ω) and 3D-printed Proto-pasta® (3750 Ω) electrodes. As a proof of concept, the ciprofloxacin antibiotic, a species of multiple interest, was selected as a model molecule. Thus, a square wave voltammetry (SWV) method was proposed in the potential range + 0.9 to + 1.3 V (vs Ag|AgCl|KCl(sat)), which provided a wide linear working range (2 to 32 µmol L-1), 1.79 µmol L-1 limit of detection (LOD), suitable precision (RSD < 7.9%), and recovery values from 94 to 109% when applied to pharmaceutical and milk samples. Additionally, the sensor is free from the interference of other antibiotics routinely employed in veterinary practices. This device is disposable, cost-effective, feasibly produced in financially limited laboratories, and consequently promising for evaluation of other antibiotic species in routine applications.

3D-printed electrode an affordable sensor for sulfanilamide monitoring in breast milk, synthetic urine, and pharmaceutical formulation samples.

This paper describes a simple and cost-effective method for manufacturing a 3D-printed electrode. This electrode presented a similar design to commercial electrodes, where a stereolithography printer was used to build the electrode body using an acrylic resin. The electroactive surface was filled by a 3D-pen using a carbon black integrated polylactic acid (CB/PLA) conductive filament. After a simple and fast (400 s) surface treatment, the 3D-printed CB/PLA electrode was combined with Differential Pulse Voltammetry (DPV) technique for sulfanilamide (SAA) determination. The developed electroanalytical method was applied to breast milk, synthetic urine, and otologic solution samples, showing excellent analytical performance with a detection limit of 12 nmol L-1, wide linear range from 1 to 39.2 µmol L-1, and good precision (RSD = 1.8%, n = 10). In addition, the sensor provides fantastic selectivity towards other antibiotic classes, and when applied in spiked samples, recovery values between 93 and 108% were obtained, which demonstrated good accuracy as well as the absence of matrix effect. It is highlighted that no laborious sample preparation steps were required (simple dilution in supporting electrolyte). Thus, the proposed 3D-printed device proves to be a promising analytical tool for routine analysis.

Batch injection analysis with amperometric detection for fluoroquinolone determination in urine, pharmaceutical formulations, and milk samples using a reduced graphene oxide-modified glassy carbon electrode.

In this work, the batch injection analysis system with amperometric detection using reduced graphene oxide as a modifier of glassy carbon electrode (GCE) was investigated for the simple, fast, and sensitive monitoring of levofloxacin (LEVO) and ciprofloxacin (CIPRO) in samples of pharmaceutical formulations, synthetic urine, and milk (low- and high-fat content). LEVO and CIPRO were quantified in seven samples using amperometric measurements at +1.10 V vs Ag/AgCl, KCl(sat). The developed methods showed excellent analytical performance with limits of detection of 0.30 and 0.16 µmol L-1, linear range from 3.0 to 50 µmol L-1 and 1.0 to 50 µmol L-1, relative standard deviation below 9.7 and 3.1%, and recovery ranges ranging from 80 to 107% and from 78 to 109% for LEVO and CIPRO, respectively. In addition, the minimum sample preparation (simple dilution) combined with a high analytical frequency (130 to 180 analyses per hour) can be highlighted. Thus, the methods are promising for implementation in routine analysis and quality control to different samples.

Electrochemical methods for the determination of antibiotic residues in milk: A critical review.

Several antibiotics have been applied to veterinary medicine due to their broad-spectrum of antibacterial activity and prophylactic power. Residues of these antibiotics can be accumulated in dairy cattle, in addition to promoting contamination of the environment and, in more serious cases, in milk, causing a public health problem. Different regulatory agencies establish maximum residue limits for these antibiotics in milk, so it becomes important to develop sensitive analytical methods for monitoring these compounds. Electrochemical techniques are important analytical tools in analytical chemistry because they present low cost, simplicity, high sensitivity, and adequate analytical frequency (sample throughput) for routine analyses. In this sense, this review summarizes the state of the art of the main electrochemical sensors and biosensors, instrumental techniques, and sample preparation used for the development of analytical methods, published in the last five years, for the monitoring of different classes of antibiotics: aminoglycosides, amphenicols, beta-lactams, fluoroquinolones, sulfonamides, and tetracyclines, in milk samples. The different strategies to develop electrochemical sensors and biosensors are critically compared considering their analytical features. The mechanisms of electrochemical oxidation/reduction of the antibiotics are revised and discussed considering strategies to improve the selectivity of the method. In addition, current challenges and future prospects are discussed.

Simultaneous determination of cadmium, lead and copper in chocolate samples by square wave anodic stripping voltammetry.

In this work, an effective and simple method is proposed for the simultaneous determination of cadmium, lead and copper in chocolate samples by Square Wave Anodic Stripping Voltammetry (SWASV). An ultrasonic bath was used for the extraction of cadmium, lead and copper from fourteen chocolate samples using HNO3 solution (7 mol L-1). The electrochemical system consisted of a cell with three electrodes and HCl solution (10 mmol L-1) as the supporting electrolyte. An efficient extraction of the metals (~100%) was attained after 1 h of ultrasonic pre-treatment. Quantitative analysis was carried out by the standard addition method. Good linearity, precision and accuracy were obtained in the range of concentrations examined. The accuracy was evaluated by means of a reference sample of spiked skim milk powder (BCR 151) to prove the reliability of the method. Detection limits (LOD) of 0.089, 0.059 and 0.018 µg g-1 were found for cadmium, copper and lead, respectively, in the chocolate samples. Concentrations in chocolate samples were 4.30-138 µg g-1 for Cu and 0.83-27.9 µg g-1 for Pb, with no significant Cd. The simultaneous determination brings advantages to other methods already reported for chocolate analysis and the samples preparation proposed avoids the traditional sample mineralization step. These characteristics show this new method is especially attractive for case studies and routine analysis.

Simultaneous determination of strobilurin fungicides residues in bean samples by HPLC-UV-AD using boron-doped diamond electrode.

The aim of this paper was the development of a method for the determination of six strobilurins (fungicides) using boron-doped diamond (BDD) electrode with amperometric detection (AD) homemade coupled to high performance liquid chromatography (HPLC/UV-Vis). HPLC separation of fungicides was performed in a C18 reverse phase column using both UV and AD detectors at 200 mn and 1.9 V, respectively. The linear range for each strobilurin was from 5 to 15 mg L-1 and the correlation coefficients for all the compounds were above 0.997. Both detectors presented adequate detectability (LOD ranging from 1.33 to 1.57 µg kg-1) respecting the limits pre-established by regulatory agencies. The method was validated presenting good values of recovery and accuracy. In the spiked samples the recoveries ranged from 61.6% (trifloxystrobin) to 98.8% (azoxystrobin) for UV and 62.3% (trifloxystrobin) to 95.2% (azoxystrobin) for AD. In blanks spikes the recovery varied from 77.8% (picoxystrobin) to 88.4% (kresoxim-methyl) for UV and 76.7% (picoxystrobin) to 87.1% (dimoxystrobin) for AD. The method showed good precision (RSD < 10%). The results obtained by amperometric and UV detections were statistically comparable. Seven bean samples were analyzed to detect fungicide residues.

Direct analysis of ascorbic acid in food beverage samples by flow injection analysis using reduced graphene oxide sensor.

In this paper, a simple, sensitive and precise electroanalytical method was developed using flow injection analysis (FIA) with amperometric detection and reduced graphene oxide sensor for ascorbic acid determination in samples of multivitamin beverages, milk, fermented milk, and milk chocolate. The advantages of this sensor include a potential displacement of 450 mV and a 2-fold peak current increase for electrochemical oxidation of ascorbic acid, which resulted in a highly sensitive method. No interference of sample matrix was observed, avoiding solvent extraction procedures (samples were only diluted). The FIA allowed a high analytical frequency, approximately 96 injections per hour, together with adequate detection limit of 4.7 µmol L-1. Good precision (RSD < 7%) and accuracy (recoveries between 91 and 108%) evidenced the robustness of the method. The method was compared with ultra-fast liquid chromatography (UFLC) obtaining statistically similar results (95% confidence level). The ascorbic acid content in samples varied from 0.065 to 2.53 mmol L-1.