11 research outputs found
Bipolar Spectroelectrochemistry
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
Direct Determination of Ascorbic Acid in a Grapefruit: Paving the Way for In Vivo Spectroelectrochemistry
The
study of real samples is more complicated than the study of
other systems. However, the inherent advantages
of UVâvis 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
Simultaneous UVâVisible Absorption and Raman Spectroelectrochemistry
The
development of a new device based on the use of UVâvis
bare optical fibers in a long optical path length configuration and
the measurement of the Raman response in normal arrangement allows
us to perform UVâvis 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 UVâvis 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 at Screen-Printed Electrodes: Determination of Dopamine
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<sup>â3</sup> 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<sup>â3</sup> 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
Development of a Novel Bidimensional Spectroelectrochemistry Cell Using Transfer Single-Walled Carbon Nanotubes Films as Optically Transparent Electrodes
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 UVâvis 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 UVâvis spectral region
Study of Adenine and Guanine Oxidation Mechanism by Surface-Enhanced Raman Spectroelectrochemistry
Metal
nanoparticles are systems largely employed in surface-enhanced
Raman spectroscopy (SERS). In particular, gold nanoparticles are one
of the best substrates used in this field. In this work, the optimal
conditions for gold nanoparticles electrodeposition on single-walled
carbon nanotubes electrodes have been established to obtain the best
SERS response. Using this substrate and analyzing the changes of in
situ Raman spectra obtained at different potentials, we have been
able to explain simultaneously the oxidation mechanism of purine bases,
differentiating the oxidation intermediates and their orientation
during the different oxidation steps. Adenine orientation hardly changes
during the whole oxidation; the molecule maintains a parallel configuration
and only shows a slightly tilted orientation after the first oxidation
step. On the other hand, guanine orientation changes completely during
its oxidation. Initially, guanine is perpendicular respect to gold
nanoparticles, changing its orientation after the first oxidation
process when the molecule shows a slightly tilted orientation, and
it finishes parallel respect to the electrode surface after the second
oxidation step
Janus Electrochemistry: Asymmetric Functionalization in One Step
Janus
structures represent an overwhelming member of materials with adaptable
chemical and physical properties. Development of new synthesis routes
has allowed the fabrication of Janus architectures with specific characteristics
depending on the final applications. In the case of the membranes,
the improvement of wet routes has been limited to the capillary effect,
in which the solution can gradually penetrate through the membrane,
avoiding a double modification different at each face of the membrane.
In this work, we propose a new electrochemical methodology to circumvent
the capillary limitation and obtain a double electrochemical functionalization
in only one step in a controlled way. This innovative methodology
has been validated using a tridirectional spectroelectrochemistry
setup. Moreover, the information provided by this optical arrangement
should be especially useful for the study of the different processes
(ion transfer, assisted ion transfer, and electron transfer) that
can take place at liquid/liquid interfaces. Janus electrochemistry
allows us to modify the two faces of a free-standing single-walled
carbon nanotube electrode in a single experiment. As proof of concept,
the free-standing films have been functionalized with two different
conducting polymers, polyaniline and polyÂ(3-hexylthiophene), in one
electrochemical experiment. According to the obtained results, this
new electrochemical methodology will open new gates for the design
and functionalization of Janus materials
In-situ Evidence of the Redox-State Dependence of Photoluminescence in Graphene Quantum Dots
Changes
in the optical properties of graphene quantum dots (GQD)
during electrochemical reduction and oxidation were investigated by
photoluminescence (PL) spectroelectrochemistry, which provided direct
in situ evidence of the dependence of GQD luminescence on their redox
state. We demonstrated that GQD PL intensity was enhanced upon reduction
(quantum yield increased from 0.44 to 0.55) and substantially bleached
during oxidation (quantum yield âŒ0.12). Moreover, PL emission
blue/red-shifted upon GQD reduction/oxidation, rendering information
about electronic transitions involved in the redox processes, namely,
the Ï â Ï* and the <i>n</i> â
Ï* transitions between energy levels of the aromatic sp<sup>2</sup> domains and the functional groups, respectively. PL intensity
changes during GQD reduction/oxidation resulted from a variation in
structural changes in GQD as a result of charge injection, as corroborated
by in situ Raman spectroelectrochemistry
Silver hexacyanoferrate (II) nanocrystals as a new material to improve Raman scattering enhancement during silver surface oxidation
Raman spectroscopy is a powerful analysis technique that shows its full potential when a high amplification of the Raman signal is achieved. In this sense, Surface-Enhanced Raman scattering (SERS) has been the most widely used phenomenon for analysis. SERS provides the amplification of the Raman intensity due to the interaction of molecules with a plasmonic nanostructured surface. The enhancement of the Raman signal can be also obtained during the electrochemical oxidation of a metal electrode; this phenomenon was denoted as Electrochemical-Surface Oxidation Enhanced Raman Scattering (EC-SOERS) and yields a good Raman signal enhancement with high reproducibility. Until now, only chloride and bromide have been employed in EC-SOERS, using a silver electrode to generate silver chloride and silver bromide nanocrystals. In this work, a new EC-SOERS substrate based on the electrogeneration of silver hexacyanoferrate (II) nanocrystals is presented which provides a very sensitive Raman response. The electrogeneration of this new material can be easily followed using spectroelectrochemistry since the characteristic Raman bands of the nanocrystals lie outside of the fingerprint region used for the analysis where the detection of most of the target molecules is performed. Indigo Carmine has been selected as target molecule, obtaining a very good response at nanomolar level under Raman resonance and non-resonance conditions.</p
Raman, UVâVis absorption, and fluorescence spectroelectrochemistry for studying the enhancement of the Raman scattering using nanocrystals activated by metal cations
Raman signal enhancement is fundamental to develop different analytical tools for chemical analysis, interface reaction studies, or new materials characterization, among others. Thus, phenomena such as surface-enhanced Raman scattering (SERS) have been used for decades to increase the sensitivity of Raman spectroscopy, leading to a huge development of this field. Recently, an alternative method to SERS for the amplification of Raman signals has been reported. This method, known as electrochemical surface oxidation-enhanced Raman scattering (EC-SOERS), has been experimentally described. However, to date, it has not yet been fully understood. In this work, new experimental data that clarify the origin of the Raman enhancement in SOERS are provided. The use of a complete and unique set of combined spectroelectrochemistry techniques, including time-resolved operando UVâvis absorption, fluorescence, and Raman spectroelectrochemistry, reveals that such enhancement is related to the generation of dielectric or semiconductor nanocrystals on the surface of the electrode and that the interaction between the target molecule and the dielectric substrate is mediated by metal cations. According to these results, the interaction metal electrodeânanocrystalâmetal cationâmolecule is proposed as being responsible for the Raman enhancement in Ag and Cu substrates. Elucidation of the origin of the Raman enhancement will help to promote the rational design of SOERS substrates as an attractive alternative to the well-known SERS phenomenon.</p