1,721,399 research outputs found
Interfacial studies using drop image processing techniques
No full textA novel method for measuring the boundary tension, based on the line by line digitisation of the video image of a pendant drop, has been developed. The method is equivalent to measuring about 1000 pairs of (X,Y) coordinates of the drop profile. From this, the boundary tension can be calculated using the following computational sequence: 1) the location of the inflexion plane, 2) the calculation of the cross-sectional diameter and the slope of the tangent of the drop at the inflexion plane, 3) the calculation of the volume of fluid hanging between the inflexion plane and the apex and 4) the calculation of the boundary tension. The first part of this thesis describes this method and its mathematical basis as well as an attempt of error analysis. A description of the image recording system, the line by line digitiser and the computing equipment used is also given, together with the complete system calibration procedure. The second part is dedicated to the study of the ion free or compact layer at the interface between organic solvents having a low mutual miscibility with water and electrolyte solutions. Measurements of the surface excess concentration of water at the interface are carried out for alkali metal chloride solutions in contact with nitrobenzene, 1,2-dichloroethane and n-heptane. The results obtained indicate that the interface should be considered as a continuous transition region rather than a compact layer. The final part illustrates the possibilities of using the line by line digitiser to investigate the kinetics of adsorption at the fluid-liquid interfaces. Cytochrome-c is used in this study.</p
Additional Recent Applications and Prospects
No full textA brief overview about additional recent applications and developments of scanning electrochemical microscopy (SECM) is given in order to demonstrate to the reader the large potential and flexibility that SECM, as a technique alone or in combination with other techniques, provides. The electrode-electrolyte interface changes dynamically during almost all electrochemical processes. In order to study these changes, many efforts are being made to combine electrochemical measurements with techniques that enable the spectroscopic characterization of the electrochemical interface in real time. One approach is the in situ parallel measurement of the electrochemical reactivity and of the vibrational modes of micrometric sample sites by combining SECM with Raman spectroscopy. The implementation of electrochemical impedance microscopy (EIS) in SECM measurements is known as scanning EIS (SEIM). Finally, a conclusion is drawn with an outlook on the expected future developments and applications of SECM
Mapping the antioxidant activity of apple peels with soft probe scanning electrochemical microscopy
Full text linkWe present a non-invasive electrochemical strategy for mapping the antioxidant (AO) activity of apple peels, which counterbalances oxidative stress caused by various external effectors. Soft carbon microelectrodes were used for soft probe scanning electrochemical microscopy (SECM) enabling the gentle and scratch-free in contact mode scanning of the rough and delicate apple peels in an electrolyte solution. The SECM feedback mode was applied using ferrocene methanol (FcMeOH) as redox mediator that gets electrochemically oxidized at the soft probe and diffuses towards the apple peel where it gets regenerated by certain AOs leading to a redox mediator recycling and increased current signal. The global AO activity in the apple peel including lenticels and regions with artificially degraded AOs were mapped using the soft microelectrodes. Finally, in an apple cross-section the higher and homogeneous AO concentration in the peel with a heterogeneously decaying AO gradient towards the apple inward was visualized, demonstrating the adequate micrometer resolution of the SECM probe and the possibility to get information of the interior AO activity of the apple.LEP
Electrochemical Imaging of Cells and Tissues
No full textThe technological and experimental progress in electrochemical imaging of biological specimens is discussed with a view on potential applications for skin cancer diagnostics, reproductive medicine and microbial testing. The electrochemical analysis of single cell activity inside cell cultures, 3D cellular aggregates and microtissues is based on the selective detection of electroactive species involved in biological functions. Electrochemical imaging strategies, based on nano/micrometric probes scanning over the sample and sensor array chips, respectively, can be made sensitive and selective without being affected by optical interferences as many other microscopy techniques. The recent developments in microfabrication, electronics and cell culturing/tissue engineering have evolved in affordable and fast-sampling electrochemical imaging platforms. We believe that the topics discussed herein demonstrate the applicability of electrochemical imaging devices in many areas related to cellular functions.LEP
High-throughput scanning electrochemical microscopy brushing of strongly tilted and curved surfaces
Full text linkThe feasibility of high-throughput scanning electrochemical microscopy (SECM) of strongly tilted (tilt angles ≤4°) and curved substrates (diameter of curvature ≥9 cm) is demonstrated by brushing them with a soft linear array of carbon microelectrodes. This probe made of thin polymeric layers operates in contact regime to follow the topography of highly unconventional SECM samples while keeping an almost constant working distance. Strong slope variations of the sample lead to a slight misalignment between the axes of the positioning system and the sliding direction of the microelectrode arrays. The resulting positional offsets can be predicted and corrected to yield a correct representation of the spatial relation on the surface of the sample. Moreover, a custom-made holder system ideally suited for precise control of the soft probe inclination angle and alignment with the substrate plane was also developed to perform high-throughput SECM imaging of a 1.2 cm2 curved metallic pin within less than 2 h.LEP
Multiple scanning electrochemical microscopy mapping of tyrosinase in micro-contact printed fruit samples on polyvinylidene fluoride membrane
Full text linkHerein, we introduce three orthogonal and compatible methods for detecting tyrosinase, a key factor in fruit browning and skin disorders, with high spatial resolution by means of scanning electrochemical microscopy (SECM). All methods are performed subsequently on the same substrate area providing a wide range of relevant information. The first SECM approach that relies on the mapping of a differential pore oxygen concentration induced by the local hydrophobic changes that the adsorption of tyrosinase generates on a porous polyvinylidene fluoride (PVDF) membrane. The second approach is based on the direct monitoring of the enzymatic activity of tyrosinase by detecting amperometrically the reaction products from the enzymatic conversion of L-3,4-dihydroxyphenylalanine (L-DOPA). Finally, tyrosinase was visualized implementing a tyrosinase sandwich immunoassay readout by SECM. The multiple SECM detection strategies were successfully applied to map unequivocally the tyrosinase enzymatic activity of a micro-contact printed banana sample. Furthermore, differential pulse voltammetry and mass spectrometry analyses were employed to elucidate the nature of the electrochemical response obtained during the tyrosinase enzymatic activity experiments.LEP
Inkjet-printed microtiter plates for portable electrochemical immunoassays
Full text linkHerein, we present the large-scale fabrication of multiplexed three-electrode sensors used in a point-of-care device platform that couples a magnetic bead-based immunoassay strategy with amperometric detection for rapid and highly sensitive analysis. The multiplexed sensors consisted of eight independent electrochemical cells, each with a carbon nanotube (CNT) working electrode, CNT counter electrode and a silver-silver chloride quasi-reference electrode. The microchips were fabricated on flexible polyethylene terephthalate (PET) sheets by sequential multilayer inkjet printing (IJP) of silver, CNT and insulator inks that were either simultaneously or subsequently post-processed (e.g. through UV photo-polymerization or photonic curing). Finally, plastic wells were mounted on top of the inkjet-printed patterns to obtain an eight-well microtiter plate where each well had a solution capacity of 50 μL. Due to the high precision of the IJP process, the microtiter plates showed high reproducibility among the individual electrochemical cells (1–2% of deviation). Furthermore, the microchips can be reusable for at least up to 20 times as demonstrated herein. In a customized multichannel potentiostat with eight implemented magnets matching the positions of the working electrodes, the electrochemical readout of magnetic bead based sandwich and competitive immunoassays was successfully realized for the detection of thyroid-stimulating hormone (TSH) and atrazine (ATR) in aqueous and urine samples, respectively. The achieved limits of detection for ATR (i.e. 0.01 μg/L) and TSH (i.e. 0.5 μIU/mL) demonstrated the potential of the IJP microtiter plates for the environmental and biological quantification of analytes in a very reliable high throughput platform. This work shows that IJP has certainly reached the status of a batch production tool for electroanalytical sensing platformsLEP
Point-of-care amperometric determination of L-dopa using an inkjet-printed carbon nanotube electrode modified with dandelion-like MnO2 microspheres
No full textAn electrochemical sensor is described for the determination of L-dopa (levodopa; 3,4-dihydroxyphenylalanine). An inkjet-printed carbon nanotube (IJPCNT) electrode was modified with manganese dioxide microspheres by drop-casting. They coating was characterized by field emission scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray powder diffraction. The sensor, best operated at a working voltage of 0.3 V, has a linear response in the 0.1 to 10 μM L-dopa concentration range, a 54 nM detection limit, excellent reproducibility, repeatability and selectivity. The amperometric approach was applied to the determination of L-dopa in spiked biological fluids and displayed satisfactory accuracy and precision.LEP
Simultaneous local sensing of two chemical properties with dual Soft Probe Scanning Electrochemical Microscopy
Full text linkA new method for the rapid and economic fabrication of dual soft microelectrodes for Soft-Probe-Scanning electrochemical microscopy (Soft-Probe-SECM) and their use for the simultaneous local detection of locally generated species is presented. The process is based on encapsulating electrode wires, such as Pt, Au and carbon fiber, by UV-photo-polymerization of a dielectric material leading to two microdisc electrodes, which are individually addressable. Probe stability is realized by using a flexible plastic support. The thickness of the dielectric material that controls the distance between the microelectrodes and the substrate surface during lateral scans over a substrate in contact mode is highly controllable by the probe fabrication parameters. The thickness of the dielectric material of the soft probes fabricated here varies between 27 μm and 35 μm, while the two microelectrodes inter-distance varies between 180 μm and 250 μm. The dual soft probes combine Pt, Au and C microdiscs of different radii (12.5 μm for Pt and Au and 4 μm for C). The flexible selection of the electrode materials enables the fabrication of dual soft probes with electrode materials suitable to detect electro-active analytes of interest at solid/solution interfaces. The dual soft probes can be used in double amperometric, double potentiometric or mixed potentiometric-amperometric modes. As a proof-of concept of the latter mode, a dual platinum black/Pt (PtB/Pt)–iridium oxide/Au (IrOx/Au) soft probe is used to image in real time the chemically induced dissolution of inkjet printed silver patterns in 0.2 mM HNO3, generating locally reactive nitrogen species (RNS) and simultaneously changing the pH. RNS amounts are measured at 0.8 V (vs. Ag/AgCl, KCl, reference electrode) at the PtB/Pt microelectrode, while the corresponding pH changes are obtained from open circuit potential measurements with the IrOx/Au microelectrode
Analytical Chemistry at the Laboratoire d'Electrochimie Physique et Analytique
Full text linkThe Laboratoire d'Electrochimie Physique et Analytique (LEPA) has moved to the new Energypolis campus in Sion. This laboratory is involved in energy research in particular by studying charge transfer reactions at soft interfaces and developing interfacial redox electrocatalysis, by pioneering the concept of photo-ionic cells and by integrating redox flow batteries for the production of hydrogen at the pilot scale. Nonetheless, this laboratory has a long tradition in analytical chemistry with the development of microfabrication techniques such as laser photo-ablation, screen-printing and more recently inkjet printing for the design and fabrication of biosensors and immunosensors. As shown in the present review, the laboratory has recently pioneered new technologies for electrochemical and mass spectrometry imaging and for the screening of allergy in patients. The role of the laboratory in the Valais landscape will be to foster the collaboration with the HES to develop teaching and research in analytical chemistry as this field is a major source of employment for chemists.LEP
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