Daniel Martín-Yerga

Electrochemical determination of mercury: a review.

Mercury is a metal that has been extensively studied, in large part due to its high toxicity. Therefore, mercury levels must be monitored in different sample types using analytical methods. This review summarizes the electrochemical methods that have been used for mercury analysis in a variety of samples. A critical evaluation of the methods and electrode materials employed for mercury analysis is presented according to the following classifications: bare electrodes, chemically modified electrodes and nanostructured electrodes. The advantages and disadvantages of each type of electrode material regarding mercury analysis are also presented.

Electrochemical immunosensor for anti-tissue transglutaminase antibodies based on the in situ detection of quantum dots.

A miniaturized electrochemical biosensor array with in situ detection of quantum dots (QDs) was developed for the detection of anti-transglutaminase IgG antibodies (a celiac disease biomarker) in human sera. For the fabrication of the sensor, a 8-channel screen-printed carbon electrochemical arrays were used as transducers and modified with tissue-transglutaminase by adsorption. The immunologic reaction was carried out in a few simple steps: reaction with human serum, which contains the analyte of interest, followed by the immunoreaction with anti-human IgG labeled with CdSe/ZnS QDs and electrochemical detection of Cd(2+) released from QDs. All steps were performed on the screen-printed arrays as the solid support, and the detection of Cd(2+) was performed in situ after acid attack of the QDs without a transfer step by voltammetric stripping. The electrochemical response was correlated with the anti-transglutaminase IgG concentration. The developed electrochemical immunosensor is a trustful screening tool for celiac disease diagnosis discriminating between positive and negative sera samples with high sensitivity.

Screen-printed electrode based electrochemical detector coupled with ionic liquid dispersive liquid–liquid microextraction and microvolume back-extraction for determination of mercury in water samples

A novel approach is presented, whereby gold nanostructured screen-printed carbon electrodes (SPCnAuEs) are combined with in-situ ionic liquid formation dispersive liquid-liquid microextraction (in-situ IL-DLLME) and microvolume back-extraction for the determination of mercury in water samples. In-situ IL-DLLME is based on a simple metathesis reaction between a water-miscible IL and a salt to form a water-immiscible IL into sample solution. Mercury complex with ammonium pyrrolidinedithiocarbamate is extracted from sample solution into the water-immiscible IL formed in-situ. Then, an ultrasound-assisted procedure is employed to back-extract the mercury into 10 µL of a 4 M HCl aqueous solution, which is finally analyzed using SPCnAuEs. Sample preparation methodology was optimized using a multivariate optimization strategy. Under optimized conditions, a linear range between 0.5 and 10 µg L(-1) was obtained with a correlation coefficient of 0.997 for six calibration points. The limit of detection obtained was 0.2 µg L(-1), which is lower than the threshold value established by the Environmental Protection Agency and European Union (i.e., 2 µg L(-1) and 1 µg L(-1), respectively). The repeatability of the proposed method was evaluated at two different spiking levels (3 and 10 µg L(-1)) and a coefficient of variation of 13% was obtained in both cases. The performance of the proposed methodology was evaluated in real-world water samples including tap water, bottled water, river water and industrial wastewater. Relative recoveries between 95% and 108% were obtained.

Towards a blocking-free electrochemical immunosensing strategy for anti-transglutaminase antibodies using screen-printed electrodes.

Abstract A blocking-free one-step immunosensing strategy using 8-channel screen-printed arrays for the detection of anti-transglutaminase IgA antibodies, celiac disease biomarkers, was developed. A simple but novel immobilization approach to efficiently modify the surface of screen-printed electrodes with a recognition element was employed in order to minimize the non-specific adsorption on the electrode surface, and the optimization of a methodology without a blocking step was carried out. After the functionalization of the electrode surface with tissue-transglutaminase, two different immunoassays, using multi-step and one-step strategies, were optimized. Serum controls from a commercial ELISA kit, anti-human IgA labelled with biotin and streptavidin labelled with CdSe/ZnS quantum dots were employed as bioreagents for the immunoassay. Screen-printed arrays were used as the solid support for the immunosensor and the detection of Cd(II) was performed in situ by anodic stripping voltammetry after an acid attack of the QDs. The electrochemical response from Cd(II) was correlated with the anti-transglutaminase IgA antibody concentration. The analytical characteristics obtained for the multi-step and one-step electrochemical immunosensors allow discrimination between positive and negative serum controls, establishing this biosensor as a useful tool for the determination of celiac disease biomarkers.

Electrochemical Study and Applications of Selective Electrodeposition of Silver on Quantum Dots

In this work, selective electrodeposition of silver on quantum dots is described. The particular characteristics of the nanostructured silver thus obtained are studied by electrochemical and microscopic techniques. On one hand, quantum dots were found to catalyze the silver electrodeposition, and on the other hand, a strong adsorption between electrodeposited silver and quantum dots was observed, indicated by two silver stripping processes. Nucleation of silver nanoparticles followed different mechanisms depending on the surface (carbon or quantum dots). Voltammetric and confocal microscopy studies showed the great influence of electrodeposition time on surface coating, and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the initial formation of Janus-like Ag@QD nanoparticles in this process. By use of moderate electrodeposition conditions such as 50 μM silver, -0.1 V, and 60 s, the silver was deposited only on quantum dots, allowing the generation of localized nanostructured electrode surfaces. This methodology can also be employed for sensing applications, showing a promising ultrasensitive electrochemical method for quantum dot detection.

Time-Resolved Luminescence Spectroelectrochemistry at Screen-Printed Electrodes: Following the Redox-Dependent Fluorescence of [Ru(bpy)3]2+

In this work, a compact instrument for time-resolved luminescence spectroelectrochemistry using low-cost disposable electrodes is reported. This instrument can be coupled with screen-printed electrodes via a specific cell and a reflection probe, which allows one to observe changes occurring at the electrode/solution interface. This approach allowed one to follow the fluorescence variation of electrofluorochromic species such as [Ru(bpy)3]2+ at screen-printed carbon electrodes. A strong correlation between the electrochemical processes and the fluorescence was found during potentiostatic or multipulsed amperometric measurements. A decrease of the fluorescence was observed when the [Ru(bpy)3]2+ was oxidized to [Ru(bpy)3]3+ and part of this fluorescence is recovered when [Ru(bpy)3]3+ was reduced to the initial species. Moreover, a significant increment of the fluorescence was found when the oxygen reduction reaction takes place, which also confirms its quenching effect. Finally, multipulsed amperometric detection was employed in order to obtain more information about the redox-dependent luminescence of [Ru(bpy)3]2+ finding a continuous quenching over time attributed to bleaching chlorine-based species.

Electrodeposition of nickel nanoflowers on screen-printed electrodes and their application to non-enzymatic determination of sugars

In this work, the electrodeposition of nickel on screen-printed carbon electrodes was carried out. As the main novelty, a galvanostatic electrodeposition methodology (application of a constant current for a specific time) was chosen to perform the electrodeposition from a Ni(II) solution. Interestingly, these conditions were able to generate nickel nanoflowers of 160 nm all over the surface. The nickel nanoflowers showed a great electrocatalytic effect towards the oxidation of reducing sugars. After the characterization of the electrode surface and the optimization of the experimental conditions, the non-enzymatic electrochemical device was employed for the determination of reducing sugars. A linear range of 25–1000 μM was obtained, showing good performance for the determination of sugars at low concentrations. The reproducibility was 5.5% (intraelectrode) and 6.9% (interelectrode), indicating a high precision using the same or different devices. After fabrication, the electrode is stable at least for 35 days, even using the same device to carry out measurements on different days. Real food samples such as honey and orange juice were also evaluated with the nickel nanoflower electrochemical device.

Evaluation of electrochemical, UV/VIS and Raman spectroelectrochemical detection of Naratriptan with screen-printed electrodes

Naratriptan, active pharmaceutical ingredient with antimigraine activity was electrochemically detected in untreated screen-printed carbon electrodes (SPCEs). Cyclic voltammetry and differential pulse voltammetry were used to carry out quantitative analysis of this molecule (in a Britton-Robinson buffer solution at pH 3.0) through its irreversible oxidation (diffusion controlled) at a potential of +0.75V (vs. Ag pseudoreference electrode). Naratriptan oxidation product is an indole based dimer with a yellowish colour (maximum absorption at 320nm) so UV-VIS spectroelectrochemistry technique was used for the very first time as an in situ characterization and quantification technique for this molecule. A reflection configuration approach allowed its measurement over the untreated carbon based electrode. Finally, time resolved Raman Spectroelectrochemistry is used as a powerful technique to carry out qualitative and quantitative analysis of Naratriptan. Electrochemically treated silver screen-printed electrodes are shown as easy to use and cost-effective SERS substrates for the analysis of Naratriptan.

Galvanostatic electrodeposition of copper nanoparticles on screen-printed carbon electrodes and their application for reducing sugars determination

In this work, a novel method for the galvanostatic electrodeposition of copper nanoparticles on screen-printed carbon electrodes was developed. Nanoparticles of spherical morphology with sizes between 60 and 280nm were obtained. The electrocatalytic effect of these copper nanospheres towards the oxidation of different sugars was studied. Excellent analytical performance was obtained with the nanostructured sensor: low detection limits and wide linear ranges (1-10,000µM) were achieving for the different reducing sugars evaluated (glucose, fructose, arabinose, galactose, mannose, xylose) with very similar calibration slopes, which demonstrates the possibility of total sugar detection. The reproducibility of these sensors was 4.4% (intra-electrode) and 7.2% (inter-electrode). The stability of the nanostructured electrodes was at least 30 days, even using the same device on different days. Several real samples (honey, orange juice and normal and sugar-free soft drinks) were evaluated to study the reliability of the nanostructured sensor.

Competitive electrochemical biosensing of biotin using cadmium-modified titanium phosphate nanoparticles and 8-channel screen-printed disposable electrodes

In this work, a method for the detection of biotin was developed using a competitive electrochemical biosensor and cadmium-modified titanium phosphate nanoparticles (CdTiPNPs) as detection labels. The electrochemical behaviour of CdTiPNPs was studied and a method for the detection of very low concentrations of these nanoparticles by anodic stripping voltammetry was optimized. After their modification with neutravidin, the nanoparticles were used as labels for the biotin competitive biosensor, which was carried out on the surface of disposable 8-channel screen-printed cards modified with biotinylated albumin. These devices allowed the detection of eight samples simultaneously, and a limit of detection in the order of 1 nM of biotin was obtained. The method was evaluated in real samples by carrying out the determination of biotin in multivitamin tablets. These results show that CdTiPNPs can compete in terms of analytical performance with quantum dots as detection labels, but the methodology is simpler since the typical acid digestion step to release the metals into the solution is not necessary.