Electrochemical monitoring of levofloxacin using a silver nanoparticle-modified disposable device based on a lab-made conductive ink.

The emergence of bacteria genetically resistant to first- and second-generation fluoroquinolones has resulted in increased consumption of levofloxacin (LEV) in human and veterinary medicine. In this regard, the development of low cost and good sensitivity electrochemical devices has been highly required. Thus, in this work, we propose the development of a disposable electrochemical device (DED) using a lab-made conductive ink based on graphite powder and nail polish immobilized on a rigid polyvinyl chloride support (transparent sheet). Additionally, a simple and quick protocol for the electrodeposition of silver nanoparticles was used in order to improve the electroanalytical performance of the sensor (2.75-fold). A differential pulse voltammetry (DPV) method was optimized and the sensor was applied for LEV monitoring in pharmaceutical formulation samples, synthetic urine and simulated body fluid. The method showed a wide linear working range ranging from 0.5 to 50 µmol L-1 and a detection limit of 68.3 nmol L-1. Furthermore, the precision was adequate (RSD < 4.7%), while the accuracy was evaluated through spiked samples with percent recovery ranging from 93 to 103%. The sensor was also shown to be selective for LEV against other electroactive antibiotic species, thus demonstrating suitable characteristics for electroanalytical applications.

A pencil graphite-based disposable device for electrochemical monitoring of sulfanilamide in honey and water samples.

The present paper reports a simple, fast, and inexpensive process of manufacturing a disposable pencil graphite electrode (PGE) from widely available materials, which showed a reproducibility of at least 7.5%. The electrode was compared to the commercial glassy carbon electrode (GCE) and showed superior electroanalytical performance for sulfanilamide (SFA) with approximately 3.9-fold higher current density. Additionally, a displacement of the oxidation peak from approximately 80 mV to more cathodic regions was observed. Therefore, a method based on square wave voltammetry (SWV) was developed for the determination of the antimicrobial SFA in honey and tap water samples using the proposed sensor. The optimized method presented good detectability (LOD = 2.37 µmol L-1), with excellent precision and accuracy (relative standard deviation < 4.2%) and percent recovery from spiked samples ranging from 92 to 97%. In addition, the sensor did not suffer significant interference from sample matrix components and other commonly evaluated antimicrobials, which demonstrates the potential of these electrodes for implementation in routine analysis and quality control.

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.