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Abstract: We report the development of a simple analytical method that offers reagentless sensing capabilities by using a copper sensor for monitoring melamine. In this method, the anodic dissolution of the copper electrode is initiated electrochemically to release copper ions, which form the melamine chloride copper ionic pair at the electrode surface. After this process, the melamine chloride copper ionic pair can be reduced electrochemically at the surface of the electrode and quantified under the optimized conditions. This protocol eliminates the necessity to contaminate the sample with a copper salt, making the method proposed herein more environmentally benign than other techniques. The elucidation of the electrochemical reduction process of the melamine copper ionic pair was investigated with an electrochemical quartz crystal microbalance (EQCM). The quantification of melamine in milk was performed using differential pulse voltammetry, where the peak current response was found to increase linearly with melamine concentration over the range 5–90μmolL−1. The repeatability of the electrode response was evaluated as 1% (n=20), and the detection limit of the proposed method was estimated to be 0.85μmolL−1 (3σ/slope). The accuracy of the proposed method was evaluated using milk samples and an addition and recovery protocol. [Copyright &y& Elsevier]

This study describes the development of electrochemical paper-based analytical devices (ePADs) using carbon-based paste combining silicone glue and graphite powder. The ePADs were manufactured using the screen-printing technique, which consisted of depositing the conductive ink on a screencast on the paper surface. In addition, an alternative electrical connector was designed and 3D-printed to make the detection method cheaper, portable and reproducible. The morphological, structural, and electrochemical properties of the conductive material developed were investigated through scanning electron microscopy (SEM), Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) measurements. The ePADs combined with the alternative connector revealed high repeatability, reproducibility, and stable responses considering a well-known redox probe ([Fe(CN) 6 ]4-/3-). In addition, the proposed ePAD provided a linear response for standard solutions of ascorbic acid (AA) in the concentration range between 0.1 and 2.0 mmol L−1. The achieved limit of detection was 4.0 μmol L−1. As proof of applicability, the ePADs were evaluated for AA analysis in synthetic biofluids (blood plasma and urine), vitamin C tablets, and food (gelatine and orange juice) samples. The analytical parameters of the proposed device were compared with other reports in the literature and exhibited similar or even superior performance, highlighting its feasibility for sensing applications. [Display omitted] • A carbon-based ink prepared by mixing graphite powder and silicone glue was used to develop screen-printed electrodes on paper. • An inexpensive 3D printed holder ensured simple assembling and suitable reproducibility. • Paper-based sensors revealed great stability and analytical performance. • Ascorbic acid was successfully determined in different samples. [ABSTRACT FROM AUTHOR]

A new method to manufacture electrochemical devices based on the graphite and colorless nail polish (N-grap) film was developed for tartrazine (Tz) detection. Scanning Electron Microscopy (SEM) demonstrates that the composite material presents a high porous carbon structure. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were employed to electrochemically characterize the electrode material, which corroborates the porous structure of the N-graph due to the enhanced electroactive area (5.4-fold increase) and presented a heterogeneous electron transfer rate constant (k0) of 5.82 × 10−3 cm s−1 for potassium ferricyanide. The electrochemical determination of the Tz was carried out using square-wave voltammetry (SWV), under the optimized experimental conditions, which showed high sensitivity (0.793 A L mol−1) and a lower limit of detection (LOD) of 2.10 × 10−8 mol L−1 with a linear concentration ranging from 2.0 to 50.0 μmol L−1. The developed sensor was applied for the analysis of Tz in sports drink samples and the result obtained by N-grap device was statistically compared with a spectrophotometric method demonstrating good accordance and the accuracy of the proposed method. Based on these results, we believe that this new fabrication method to produce disposable and low-cost electrochemical devices can be an alternative method for in-field analysis of dye in commercial sport drink samples and other relevant applications. [Display omitted] • A simple method to fabricate disposable and low-cost electrochemical devices using graphite and nail polish is reported. • The composite material presented a porous carbon structure that exhibits high electron transfer kinetics. • The proposed sensor was successfully applied to the sensitive analysis of tartrazine (Tz) in sports drink samples. • The proposed method is reproducible, robust, accurate, and suitable for routine analysis. [ABSTRACT FROM AUTHOR]