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.

Adsorptive stripping voltammetric determination of chloramphenicol residues in milk samples using reduced graphene oxide sensor.

In this paper, the electrochemical response of chloramphenicol (CHL) was investigated on a bare glassy carbon electrode (GCE) and after modification with reduced graphene oxide (GCE/rGO). Preliminary studies by cyclic voltammetry demonstrated an adsorption-controlled mass transport regime of CHL species and a pH-dependent behavior on both electrode surfaces. An adsorptive stripping differential pulse voltammetry (AdSDPV) method was proposed and under optimized instrumental conditions, a comparison of the analytical characteristics of both sensors was performed. The GCE/rGO sensor showed an increase in sensitivity (10-fold), and an anticipation of the reduction potential (200 mV), compared to the bare electrode, due to the adsorptive character (pre-concentration of the CHL species) and the electrocatalytic effect of the nanomaterial. The method was applied to skimmed and whole milk samples, which were simply diluted (50-fold) in supporting electrolyte. The results by AdSDPV using GCE/rGO showed adequate detectability (0.22 µmol L-1), good precision with a 6% relative standard deviation (RSD) and satisfactory recovery ranging from 93 to 108%. The obtained results were statistically similar (95% confidence level) with those performed through ultra-fast liquid chromatography (UFLC). Furthermore, the sensor showed an improvement in the analytical performance for CHL detection, when compared to other sensors reported in the literature. Therefore, the developed method is reliable and promising for implementation in monitoring CHL residues in milk 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.