by Keyword: Electrochemistry
Checa, M., Millan-Solsona, R., Gomila, G., (2019). Frequency-dependent force between ac-voltage-biased plates in electrolyte solutions Physical Review E 100, (2), 022604
We analyze the frequency dependence of the force between ac-voltage-biased plates in electrolyte solutions. To this end we solve analytically the Poisson-Nernst-Planck transport model in the dilute concentration and low voltage regime for a 1:1 symmetric electrolyte with blocking electrodes under a dc+ac applied voltage. The total force, which is the resultant of the electric and osmotic forces, shows a complex dependence on plate separation, frequency, ion concentration, and compact layer properties, different from that predicted from electrostatic current models or equivalent circuit models, due to the relevance of the osmotic force contribution in almost the whole range of frequencies. For the total dc force, we show that it decays at fixed ion concentration, linearly with plate separation for separations larger than a few times the Debye screening length. This linear dependence is due to the assumption about the conservation of the number of ions in the system. Moreover, the 1ω and 2ω ac harmonics of the total force show a broad peak at intermediate frequencies; it is centered at about the inverse of the charging time of the double layer capacitance, and covers the frequency range between the inverse of the diffusion time and the inverse of the electrolyte dielectric relaxation time. Finally, the 1ω ac harmonic component attains its high frequency asymptotic value at frequencies much higher than the inverse of the electrolyte dielectric relaxation time due to the very slow relaxation of the osmotic 1ω harmonic component at high frequencies. The derived analytical expressions for the total force remain valid up to voltages of the order of the thermal voltage, as has been assessed by means of numerical calculations. The numerical calculations are also used to explore the onset of higher force harmonics for larger applied voltages. Understanding the frequency dependence of the force acting on voltage-biased plates in electrolyte solutions can be of relevance for electrical actuation strategies in microelectromechanical systems and for the interpretation of some emerging electric scanning probe force microscopy techniques operating in electrolyte solutions.
Keywords: Electrochemistry, Statistical physics
Pérez, Judit, Dulay, Samuel, Mir, M., Samitier, Josep, (2018). Molecular architecture for DNA wiring Biosensors and Bioelectronics 121, 54-61
Detection of the hybridisation events is of great importance in many different biotechnology applications such as diagnosis, computing, molecular bioelectronics, and among others. However, one important drawback is the low current of some redox reporters that limits their application. This paper demonstrates the powerful features of molecular wires, in particular the case of S-[4-[2-[4-(2-Phenylethynyl)phenyl]ethynyl]phenyl] thiol molecule and the key role that play the nanometric design of the capture probe linkers to achieve an efficient couple of the DNA complementary ferrocene label with the molecular wire for an effective electron transfer in co-immobilised self-assembled monolayers (SAMs) for DNA hybridisation detection. In this article, the length of the linker capture probe was studied for electron transfer enhancement from the ferrocene-motifs of immobilised molecules towards the electrode surface to obtain higher kinetics in the presence of thiolated molecular wires. The use of the right couple of capture probe linker and molecular wire has found to be beneficial as it helps to amplify eightfold the signal obtained.
Keywords: DNA hybridisation, Bioelectronics, Electron transfer rate constant, Molecular wires, Electrochemistry, Ferrocene, Biosensor
Ino, Kosuke, Nashimoto, Yuji, Taira, Noriko, Ramón-Azcon, Javier, Shiku, Hitoshi, (2018). Intracellular electrochemical sensing Electroanalysis 30, (10), 2195-2209
Observing biochemical processes within living cell is imperative for biological and medical research. Fluoresce imaging is widely used for intracellular sensing of cell membranes, nuclei, lysosomes, and pH. Electrochemical assays have been proposed as an alternative to fluorescence-based assays because of excellent analytical features of electrochemical devices. Notably, thanks to the rapid progress of micro/nanotechnologies and electrochemical techniques, intracellular electrochemical sensing is making rapid progress, leading to a successful detection of intracellular components. Such insight can provide a deep understanding of cellular biological processes and, ultimately, define the human healthy and diseased states. In this review, we present an overview of recent research progress in intracellular electrochemical sensing. We focus on two main topics, electrochemical extraction of cytosolic contents from cells and intracellular electrochemical sensing in situ.
Keywords: Micro/nanoelectrode, Analytical electrochemistry, Intracellular sensing, Cell analysis
Galán, T., Prieto-Simón, B., Alvira, M., Eritja, R., Götz, G., Bäuerle, P., Samitier, J., (2015). Label-free electrochemical DNA sensor using "click"-functionalized PEDOT electrodes Biosensors and Bioelectronics 74, 751-756
Here we describe a label-free electrochemical DNA sensor based on poly(3,4-ethylenedioxythiophene)-modified (PEDOT-modified) electrodes. An acetylene-terminated DNA probe, complementary to a specific "Hepatitis C" virus sequence, was immobilized onto azido-derivatized conducting PEDOT electrodes using "click" chemistry. DNA hybridization was then detected by differential pulse voltammetry, evaluating the changes in the electrochemical properties of the polymer produced by the recognition event. A limit of detection of 0.13. nM was achieved using this highly selective PEDOT-based genosensor, without the need for labeling techniques or microelectrode fabrication processes. These results are promising for the development of label-free and reagentless DNA hybridization sensors based on conducting polymeric substrates. Biosensors can be easily prepared using any DNA sequence containing an alkyne moiety. The data presented here reveal the potential of this DNA sensor for diagnostic applications in the screening of diseases, such as "Hepatitis C", and genetic mutations.
Keywords: Azido-EDOT, Click chemistry, Differential pulse voltammetry, DNA biosensor, Electrochemistry, Hepatitis C virus
Pardo, W. A., Mir, M., Samitier, J., (2015). Signal enhancement in ultraflat electrochemical DNA biosensors Electrophoresis , 36, (16), 1905-1911
The ability of holding back the undesired molecules, but at the same time to provide the right distribution and orientation of the bioreceptors, are critical targets to reach an efficient hybridization and enhanced detection in electrochemical DNA biosensors. The main actors responsible of these key functions are the substrate of the sensor and the interface auto-assembled on it. In this paper we present the annealing as a method to improve commercial gold evaporated substrates for biosensor applications. The restructuring of granulated gold surface by means of annealing heating treatment leads to the formation of ultraflat gold lamellar terraces. The formation of terraces was characterized with scanning tunneling microscopy and optical interferometry. The performance of the sensor sensitivity on granular substrates and ultraflat substrates was studied, concerning the orientation and surface coverage of the bioreceptor interface applied in electrochemical biosensor. The hybridization efficiency of ferrocene-labeled DNA amplified by PCR was characterized with surface plasmon resonance and electrochemistry. The experimental results demonstrate that annealing process, positive influence on optical and voltammetric readings, due to a structured organization of the bioreceptors on the flat substrate, gaining more efficient immobilization and DNA hybridization. The results suggest the annealing as a powerful tool for improving gold substrates in biosensors applications.
Keywords: Annealing ultraflat surfaces, DNA biosensor, DNA hybridization, Electrochemistry, Self-assembled monolayer
Artés, J. M., López-Martínez, M., Díez-Pérez, I., Sanz, F., Gorostiza, P., (2014). Nanoscale charge transfer in redox proteins and DNA: Towards biomolecular electronics Electrochimica Acta 140, 83-95
Understanding how charges move through and between biomolecules is a fundamental question that constitutes the basis for many biological processes. On the other hand, it has potential applications in the design of sensors based on biomolecules and single molecule devices. In this review we introduce the study of the electron transfer (ET) process in biomolecules, providing an overview of the fundamental theory behind it and the different experimental approaches. The ET in proteins is introduced by reviewing a complete electronic characterization of a redox protein (azurin) using electrochemical scanning tunnelling microscopy (ECSTM). The ET process in DNA is overviewed and results from different experimental approaches are discussed. Finally, future directions in the study of the ET process in biomolecules are introduced as well as examples of possible technological applications.
Keywords: Bioelectrochemistry, Biomolecular electronics, Charge transfer, Nanobiodevice, Single-molecule junction
Mir, M., Lugo, R., Tahirbegi, I. B., Samitier, J., (2014). Miniaturizable ion-selective arrays based on highly stable polymer membranes for biomedical applications Sensors 14, (7), 11844-11854
Poly(vinylchloride) (PVC) is the most common polymer matrix used in the fabrication of ion-selective electrodes (ISEs). However, the surfaces of PVC-based sensors have been reported to show membrane instability. In an attempt to overcome this limitation, here we developed two alternative methods for the preparation of highly stable and robust ion-selective sensors. These platforms are based on the selective electropolymerization of poly(3,4-ethylenedioxythiophene) (PEDOT), where the sulfur atoms contained in the polymer covalently interact with the gold electrode, also permitting controlled selective attachment on a miniaturized electrode in an array format. This platform sensor was improved with the crosslinking of the membrane compounds with poly(ethyleneglycol) diglycidyl ether (PEG), thus also increasing the biocompatibility of the sensor. The resulting ISE membranes showed faster signal stabilization of the sensor response compared with that of the PVC matrix and also better reproducibility and stability, thus making these platforms highly suitable candidates for the manufacture of robust implantable sensors.
Keywords: Biomedicine, Electrochemistry, Endoscope, Implantable device, Ion-selective electrode (ISE) sensor, Ischemia, pH detection, Biocompatibility, Chemical sensors, Electrochemistry, Electrodes, Electropolymerization, Endoscopy, Functional polymers, Implants (surgical), Ion selective electrodes, Medical applications, Polyvinyl chlorides, Stabilization, Biomedical applications, Biomedicine, Implantable devices, Ion selective sensors, Ischemia, Membrane instability, pH detection, Poly(3 ,4 ethylenedioxythiophene) (PEDOT), Ion selective membranes
Tahirbegi, I. B., Alvira, M., Mir, M., Samitier, J., (2014). Simple and fast method for fabrication of endoscopic implantable sensor arrays Sensors 14, (7), 11416-11426
Here we have developed a simple method for the fabrication of disposable implantable all-solid-state ion-selective electrodes (ISE) in an array format without using complex fabrication equipment or clean room facilities. The electrodes were designed in a needle shape instead of planar electrodes for a full contact with the tissue. The needle-shape platform comprises 12 metallic pins which were functionalized with conductive inks and ISE membranes. The modified microelectrodes were characterized with cyclic voltammetry, scanning electron microscope (SEM), and optical interferometry. The surface area and roughness factor of each microelectrode were determined and reproducible values were obtained for all the microelectrodes on the array. In this work, the microelectrodes were modified with membranes for the detection of pH and nitrate ions to prove the reliability of the fabricated sensor array platform adapted to an endoscope.
Keywords: Chemical sensors, Cyclic voltammetry, Electrochemistry, Endoscopy, Fabrication, Implants (surgical), Microelectrodes, Needles, Nitrates, Scanning electron microscopy, Biomedicine, Fabricated sensors, Fabrication equipment, Implantable devices, Implantable sensors, Optical interferometry, Planar electrode, Roughness factor, Ion selective electrodes
Torrent-Burgués, J., Cea, P., Giner, I., Guaus, E., (2014). Characterization of Langmuir and Langmuir-Blodgett films of an octasubstituted zinc phthalocyanine Thin Solid Films , 556, 485-494
In this work we report the fabrication of Langmuir and Langmuir-Blodgett (LB) films of a substituted ZnPc (octakis(oxyoctyl)phthalocyanine of zinc), and their characterization by means of several techniques. These characterization techniques include surface pressure (Ï€-A) and surface potential (Î”V-A) isotherms as well as UV-vis Reflection spectroscopy and Brewster Angle Microscopy (BAM) for the films at the air-water interface together with UV-vis absorption and IR spectroscopies and Atomic Force Microscopy (AFM) for the LB films. The Ï€-A and Î”V-A isotherms and BAM images indicate a phase transition at a surface pressure of ca. 9 mN/m and a multilayer formation at surface pressures around 19-20 mN/m; at a surface pressure around 27 mN/m a disordered collapse of the film occurs. In addition, AFM images of LB films at Ï€ = 10 mN/m and Ï€ = 20 mN/m show a monomolecular and a multilayered film, respectively. The comparison of the UV-vis spectrum of ZnPc in solution, the reflection spectra of the Langmuir films and UV-vis spectra of LB films reveals a significant reduction in the Q band intensity for the films, indicative of an organization of ZnPc in the Langmuir and LB films versus the random distribution in solution. The UV-vis Reflection spectra are also consistent with multilayer formation at surface pressures around 19-20 mN/m. The relative intensities of the IR spectrum bands change from the KBr pellet to the LB film which is also attributable to orientation effects in the film. Cyclic voltammetric experiments of LB films incorporating the ZnPc derivative show peaks that can be correlated with redox processes occurring in the phthalocyanine ring. A small but significant influence of the surface pressure and the number of deposited layers in the electrochemical behaviour is observed. The electrochemical response of cast films exhibits some differences with respect to that of LB films which have been attributed to their different molecular organizations.
Keywords: Atomic Force Microscopy, Electrochemistry, Langmuir-Blodgett, Multilayers, Optical spectroscopy techniques, Zinc phthalocyanine, Atomic force microscopy, Electrochemistry, Interfaces (materials), Isotherms, Multilayers, Nitrogen compounds, Optical multilayers, Organic polymers, Zinc compounds, Brewster angle microscopy, Characterization techniques, Electrochemical behaviour, Langmuir and langmuir-blodgett films, Langmuir-blodgett, Optical spectroscopy techniques, UV-Vis Reflection Spectroscopy, Zinc phthalocyanines, Langmuir Blodgett films
Artés, Juan M., Díez-Pérez, Ismael, Sanz, Fausto, Gorostiza, Pau, (2011). Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy ACS Nano 5, (3), 2060-2066
We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using
an electrochemical tunneling microscope under bipotentiostatic control, we obtained current-distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.
Keywords: Long-range electron transfer (LRET), Distance decay constant, Single-molecule electrochemistry, Redox enzyme, Metalloprotein, Blue copper protein, Azurin, Electrochemical scanning tunneling microscopy and spectroscopy, Nanoelectrodes, Debye length, Electrochemical charge screening
Mir, M., Homs, A., Samitier, J., (2009). Integrated electrochemical DNA biosensors for lab-on-a-chip devices Electrophoresis , 30, (19), 3386-3397
Analytical devices able to perform accurate and fast automatic DNA detection or sequencing procedures have many potential benefits in the biomedical and environmental fields. The conversion of biological or biochemical responses into quantifiable optical, mechanical or electronic signals is achieved by means of biosensors. Most of these transducing elements can be miniaturized and incorporated into lab-on-a-chip devices, also known as Micro Total Analysis Systems. The use of multiple DNA biosensors integrated in these miniaturized laboratories, which perform several analytical operations at the microscale, has many cost and efficiency advantages. Tiny amounts of reagents and samples are needed and highly sensitive, fast and parallel assays can be done at low cost. A particular type of DNA biosensors are the ones used based on electrochemical principles. These sensors offer several advantages over the popular fluorescence-based detection schemes. The resulting signal is electrical and can be processed by conventional electronics in a very cheap and fast manner. Furthermore, the integration and miniaturization of electrochemical transducers in a microsystem makes easier its fabrication in front of the most common currently used detection method. In this review, different electrochemical DNA biosensors integrated in analytical microfluidic devices are discussed and some early stage commercial products based on this strategy are presented.
Keywords: DNA, Electrochemical DNA biosensors, Electrochemistry, Lab-on-a-chip, Micro Total Analysis systems, Field-effect transistors, Sequence-specific detection, Chemical-analysis systems, Solid-state nanopores, Carbon nanotubes, Microfluidic device, Electrical detection, Hybridization, Molecules, Sensor