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.

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.

A new methodology is presented to offer the possibility of simultaneously obtaining two different spectroscopic signals in a single spectroelectrochemical experiment. Taking the plane of the electrode surface as a spatial reference, normal-beam and parallel-beam UV-vis absorbance signals are jointly analyzed, revealing important experimental differences between the two kinds of signals. Two different chemical systems are selected to show the possibilities of the bidimensional spectroelectrochemistry: a simple diffusive process and an adsorptive electrode reaction. Comparative results show clearly that the two kinds of spectroscopic signals, both normal and parallel to the electrode surface, have to be used together in the study of any electrode reaction scheme.

The potentiostatic electrosynthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) in aqueous media without addition to the solution of any kind of surfactant has been studied by electrochemical quartz crystal microbalance (EQCM) and by spectroelectrochemistry. These tandem techniques have given valuable new information about the electropolymerisation process, allowing us to relate absorbance-charge and frequency-charge relationships to: (i) oligomers generation and chain propagation, as far as the length leading to precipitation is reached; (ii) growing of the polymer deposit and concomitant p-doping, and even (iii) overoxidation of the polymer film. An analysis of the whole of the data, in fact, shows that the charge spent is not necessarily totally involved in the polymer deposit formation, growth, and p-doping, so that it is necessary to be particularly careful in the fitting of the experimental data to linear models.

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.