ABSTRACT: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 non-conductor and transparent supports such as polyethylene terephthalate, glass and quartz, and to conductor supports such as indium tin oxide, aluminium, 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.

The study of real samples is more complicated than the study of other systems. However, the inherent advantages of UV-vis absorption spectroelectrochemistry should overcome some difficulties related to direct measurements in complex matrices. For this reason, a singular spectroelectrochemistry device has been fabricated and validated. The novel cell is based on single-walled carbon nanotubes, which are filtered and subsequently press-transferred on a polyethylene terephthalate support using a stencil with a custom design. With this new methodology, working, counter, and reference electrodes are completely flat on the surface, where two optical fibers are fixed in a long optical path length configuration. To demonstrate the usefulness of this device and the power of spectroelectrochemistry techniques to solve problems of the current world, this device is used to quantitatively detect the concentration of ascorbic acid in a complex matrix such as a fruit, directly, without any previous sample pretreatment. The ease to fabricate the device, the advantages related to its use, and the excellent results obtained not only with univariate but also with multivariate analysis, shed more light on the analysis of samples as they occur in nature. According to the particular features of this cell, to the best of our knowledge this is the first spectroelectrochemical sensor that can be inserted directly in a biological matrix, laying the groundwork to perform in vivo measurements in a near future.

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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.

Spectroelectrochemistry (SEC) has been used for more than 50 years, but this set of techniques has not been widely used for quantitative analysis. For many years, no commercial instruments were available, which made very difficult to spread the use of SEC. Nowadays, only the creativity of the researchers is required to exploit the capabilities of SEC. This review is written with the aim of showing the potential of SEC, mainly for analytical chemistry. Here, we explain what SEC is, how analytical responses can be obtained, why these techniques are useful for sensors, with a brief description of its advantages in use, and, finally, we try to show the challenges that must be addressed in the next years. SEC can resolve interesting analytical problems using the high amount of data provided by this intrinsic trilinear technique. Given the quantitative analysis point of view of this review, the discussion of the SEC techniques is focused on UV/Vis absorption, photoluminescence and Raman SEC.