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Bipolar electrochemistry is receiving growing attention in the last years, not only because it is an important tool for studying electron transfer processes, but also because it is really fruitful in the development of new analytical sensors. Bipolar electrodes show promising applications as a direct analytical tool since oxidation and reduction reactions take place simultaneously on different parts of a single conductor. There are several electrochemical devices that provide information about electron transfer between two immiscible electrolyte solutions, but to the best of our knowledge, this is the first time that a bipolar device is able to record two spectroelectrochemical responses concomitantly at two different compartments. It allows deconvolving the electrochemical signal into two different optical signals related to the electron transfer processes occurring at two compartments that are electrically in contact. The combination of an electrochemical and two spectroscopic responses is indeed very useful, providing essential advantages in the study of a huge variety of systems. The study of three different electrochemical systems, such as reversible redox couples, carbon nanotubes, and conducting polymers has allowed us to validate the new cell and to demonstrate the capabilities of this technique to obtain valuable time-resolved information related to the electron transfer processes., Ministerio de Economía y Competitividad (CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT) and Junta de Castilla y León (BU033-U16)

The development of a new device based on the use of UV–vis bare optical fibers in a long optical path length configuration and the measurement of the Raman response in normal arrangement allows us to perform UV–vis and Raman spectroelectrochemistry simultaneously in a single experiment. To the best of our knowledge, this is the first time that a spectroelectrochemistry device is able to record both spectroscopic responses at the same time, which further expands the versatility of spectroelectrochemistry techniques and enables us to obtain much more high-quality information in a single experiment. Three different electrochemical systems, such as ferrocyanide, dopamine, and 3,4-ethylenedioxythiophene, have been studied to validate the cell and to demonstrate the performance of the device. Processes that take place in solution can be properly distinguished from processes that occur on the electrode surface during the electrochemical experiment, providing a whole picture of the reactions taking place at the electrode/solution interface. Therefore, this device allows us to study a larger number of complex electrochemical processes from different points of view taking into account not only the UV–vis spectral changes in the solution adjacent to the electrode but also the Raman signal at any location. Furthermore, complementary information, which could not be unambiguously extracted without considering together the two spectroscopic signals and the electrochemical response, is obtained in a novel way., Ministerio de Economia y Competitividad (Grants CTQ2014-55583-R, CTQ2014-61914-EXP, and CTQ2015-71955-REDT)

Novel single-walled carbon nanotube press-transfer electrodes (SW-PTEs) for microfluidic sensing are proposed. In this approach, carbon nanotubes are press-transferred on poly(methyl methacrylate) (PMMA) substrates and are easily coupled to microfluidic chips and act as the exclusive transducer in electrochemical sensing. The detector design consisted of a press-transferred SW film (7 mm × 1 mm) positioned and centered on the PMMA substrate (33 mm × 9 mm). The analytical performance of the SW-PTEs was deeply evaluated using two commercial SWs sources and employing a mixture of dopamine and catechol as model analytes. Analyte detection was influenced by the volume of commercial SW dispersion used in the fabrication of SW-PTEs, with 5 mL taken from a dispersion of 0.5 mg/100 mL being the most favorable volume. In addition, excellent repeatability (relative standard deviation (RSD) of ≤7%, n = 5), interelectrodes reproducibility (RSD ≤ 9%, n = 5), and an extreme resistance to fouling were obtained even after 1 h of microchip analysis with RSD values of ≤4% and ≤9% (n = 15) for migration times and peak heights, respectively. Good sensitivity, remarkable signal-to-noise characteristics, and a well-defined linear concentration dependence (r ≥ 0.990) was also obtained, which allowed these novel detectors to be considered as valuable tools for quantitative analysis. Analytical characterization of the SW-PTEs by field-emission scanning electron microscopy (FESEM) revealed individual bundles of SWs that were highly ordered over the PMMA at the background where the SW bundles were embedded on the PMMA substrate, giving the electrode a high stability. Furthermore, the laboratory-fabricated SW-PTEs can be afforded in any laboratory since they do not require clean-room facilities and are highly compatible with microfluidic scale, mass production, and disposability. In addition, the proposed approach draws new and exciting horizons for electrochemical microfluidic sensing, such as the use of other pure or hybrid nanomaterials and also the possibilities to incorporate biomolecules for highly selective sensing.

A really easy method to transfer commercial single-walled carbon nanotubes (SWCNTs) to different substrates is proposed. In this paper, a homogeneous transference of SWCNTs films to nonconductor and transparent supports, such as polyethylene terephthalate, glass, and quartz, and to conductor supports, such as indium tin oxide, aluminum, highly ordered pyrolytic graphite, and glassy carbon, was achieved using a very fast, reproducible, and clean methodology. In order to test these transferences, SWCNTs films transferred on quartz were used as working optically UV–vis transparent electrodes due to their optimal electrical and optical properties. A new easy-to-use, homemade optical fiber based cell for bidimensional spectroelectrochemistry was developed, offering the possibility to measure in normal and parallel configuration. The cell was tested with ferrocenemethanol, a compound widely used in electrochemistry but scarcely studied by spectroelectrochemistry, covering the UV–vis spectral region., Ministerio de Economia y Competitividad (CTQ2010-17127) and Junta de Castilla y Leon (GR71, BU349-U13) is gratefully acknowledged. J.G.-R. thanks Ministerio de Educacion, Cultura y Deporte for his FPU fellowship. B.D.B. Aaronson and Patrick R. Unwin are gratefully acknowledged for taking the FE-SEM images in the University of Warwick, This document is the Accepted Manuscript version of a Published Work that appeared in final form in Analytical Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher

A new device to perform spectroelectrochemical measurements in the UV/visible spectral region using screen-printed electrodes has been developed. Neurotransmitter dopamine has been selected as a proof of concept of the capabilities of the new device. The results obtained have allowed us both to study the oxidation mechanism of dopamine and to carry out the spectroelectrochemical detection of this neurotransmitter. Differences in dopamine oxidation mechanism have been observed depending on the initial concentration. Thus, dopamine concentrations lower than 10(-3) M led to a higher generation of dopaminochrome and its derivatives with a band centered at 305 nm, which was the best wavelength to determine dopamine spectrophotometrically at these concentrations. However, if dopamine concentration is higher than 10(-3) M, dopaminoquinone is stable enough to use its maximum of absorbance, 395 nm, to detect this neurotransmitter. Dopamine concentration can also be calculated from the electrochemical data in spectroelectrochemistry, the results being comparable to that obtained from spectroscopic data. Comparison between spectrophotometric and electrochemical determinations demonstrates that the two methods measure this analyte indistinctively, proving that spectroelectrochemistry represents an autovalidated technique. Partial least-squares regression has also been used, obtaining good results in the full dopamine concentration range. Finally, as spectroelectrochemistry is an intrinsically trilinear technique, PARAFAC has been used to study the effect of probable interfering species.

Spatial scanning spectroelectrochemistry is a new analytical technique that provides spectral information at different distances from an electrified liquid/liquid interface where an electrochemical process takes place. As a proof of concept, we have studied two different electrochemical processes at the electrified liquid/liquid interface: (1) Ru(bpy)(3)(2+) transfer through the water/1,2-dichloroethane interface and (2) electrodeposition of Pd nanoparticles at the water/1,2-dichloroethane interface. The instrumental setup developed consists of a movable slit for the light beam to sample at well-defined positions on both sides of the interface, providing important information about the chemical process occurring. If the slit is scanned at different distances from the interface during an electrochemical experiment, a complete picture of the reactions and equilibria in the diffusion layer can be obtained. For example, in the case of the Ru(bpy)(3)(2+), the experiments show clearly how the complex is transferred from one phase to the other. In the case of electrosynthesis of Pd nanoparticles, it is demonstrated that nanoparticles are not only deposited at the interface but diffuse to the aqueous bulk solution. These in situ observations were confirmed by ex situ experiments using transmission electron microscopy.