Analytical Methods for the Determination of Major Drugs Used for the Treatment of COVID-19. A Review.

At the beginning of the COVID-19 outbreak (end 2019 - 2020), therapeutic treatments based on approved drugs have been the fastest approaches to combat the new coronavirus pandemic. Nowadays several vaccines are available. However, the worldwide vaccination program is going to take a long time and its success will depend on the vaccine public's acceptance. Therefore, outside of vaccination, the repurposing of existing antiviral, anti-inflammatory and other types of drugs, have been considered an alternative medical strategy for the COVI-19 infection. Due to the broad clinical potential of the drugs, but also to their possible side effects, analytical methods are needed to monitor the drug concentrations in biological fluids and pharmaceutical products. This review deals with analytical methods developed in the period 2015 - July 2021 to detect potential drugs that, according to a literature survey, have been taken into consideration for the treatment of COVID-19. The drugs considered here have been selected on the basis of the number of articles published in the period January 2020-July 2021, using the combination of the keywords: COVID-19 and drugs or SARS-CoV-2 and drugs. A section is also devoted to monoclonal antibodies. Over the period considered, the analytical methods have been employed in a variety of real samples, such as body fluids (plasma, blood and urine), pharmaceutical products, environmental matrices and food.

Label-free electrochemical aptasensor for the detection of SARS-CoV-2 spike protein based on carbon cloth sputtered gold nanoparticles.

The proliferation and transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or the (COVID-19) disease, has become a threat to worldwide biosecurity. Therefore, early diagnosis of COVID-19 is crucial to combat the ongoing infection spread. In this study we propose a flexible aptamer-based electrochemical sensor for the rapid, label-free detection of SARS-CoV-2 spike protein (SP). A platform made of a porous and flexible carbon cloth, coated with gold nanoparticles, to increase the conductivity and electrochemical performance of the material, was assembled with a thiol functionalized DNA aptamer via S-Au bonds, for the selective recognition of the SARS-CoV-2 SP. The various steps for the sensor preparation were followed by using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV). The proposed platform displayed good mechanical stability, revealing negligible changes on voltammetric responses to bending at various angles. Quantification of SARS-CoV-2 SP was performed by DPV and chronopotentiometry (CP), exploiting the changes of the electrical signals due the [Fe(CN)6]3-/4- redox probe, when SARS-CoV-2 SP binds to the aptamer immobilized on the electrode surface. Current density, in DPV, and square root of the transition time, in CP, varied linearly with the log[ SARS-CoV-2 SP], providing lower limits of detection (LOD) of 0.11 ng/mL and 37.8 ng/mL, respectively. The sensor displayed good selectivity, repeatability, and was tested in diluted human saliva, spiked with different SARS-CoV-2 SP concentrations, providing LODs of 0.167 ng/mL and 46.2 ng/mL for DPV and CP, respectively.

Controlled, partially exfoliated, self-supported functionalized flexible graphitic carbon foil for ultrasensitive detection of SARS-CoV-2 spike protein.

This paper reports on an ultrasensitive and label-free electrochemical immunosensor for monitoring the SARS-CoV-2 spike protein (SARS-CoV-2 SP). A self-supported electrode, which can simultaneously serve as an antibody immobilization matrix and electron transport channel, was initially fabricated by a controlled partial exfoliation of a flexible graphitic carbon foil (GCF). Mild acidic treatment enabled the partial oxidation and exfoliation (down to a few layers) of the flexible GCF; this also provided a high percentage of oxygen functionality and an enhanced surface roughness. The substrate electrode was further functionalized with ethylenediamine (EDA) to provide a suitable platform with even a higher surface roughness, for the covalent immobilization of an anti-SARS-CoV-2 antibody. The change in the current response for the [Fe(CN)6]3-/4- redox couple, induced by the binding of SARS-CoV-2 SP to the antibody immobilized on the electrode surface, was used to determine the SARS-CoV-2 SP concentration. The immunosensor thus prepared could detect SARS-CoV-2 SP within 30 min with high reproducibility and specificity over a wide concentration range (0.2-100 ng/mL). Detection limits of 25 pg/mL and 27 pg/mL were found in a phosphate buffer solution (pH 7.4), and diluted blood plasma, respectively. The immunosensor was also employed to detect SARS-CoV-2 SP in artificial human saliva.

COVID-19 Specific Immune Markers Revealed by Single Cell Phenotypic Profiling.

COVID-19 is a viral infection, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and characterized by a complex inflammatory process and clinical immunophenotypes. Nowadays, several alterations of immune response within the respiratory tracts as well as at the level of the peripheral blood have been well documented. Nonetheless, their effects on COVID-19-related cell heterogeneity and disease progression are less defined. Here, we performed a single-cell RNA sequencing of about 400 transcripts relevant to immune cell function including surface markers, in mononuclear cells (PBMCs) from the peripheral blood of 50 subjects, infected with SARS-CoV-2 at the diagnosis and 27 healthy blood donors as control. We found that patients with COVID-19 exhibited an increase in COVID-specific surface markers in different subsets of immune cell composition. Interestingly, the expression of cell receptors, such as IFNGR1 and CXCR4, was reduced in response to the viral infection and associated with the inhibition of the related signaling pathways and immune functions. These results highlight novel immunoreceptors, selectively expressed in COVID-19 patients, which affect the immune functionality and are correlated with clinical outcomes.

2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium.

The synthesis of Co-based two-dimensional (2D) metal azolate framework nanosheets (MAF-5-CoII NS) is described using a simple hydrothermal method. The product was isostructural to MAF-5 (Zn). The as-prepared MAF-5-CoII NS exhibited high surface area (1155 m2/g), purity, and crystallinity. The MAF-5-CoII NS-modified screen-printed electrode (MAF-5-CoII NS/SPE) was used for nonenzymatic detection of glucose in diluted human blood plasma (BP) samples with phosphate buffer saline (PBS, pH 7.4) and NaOH (0.1 M, pH 13.0) solutions. The MAF-5-CoII NS nanozyme displayed good redox activity in both neutral and alkaline media with the formation of CoII/CoIII redox pair, which induced the catalytic oxidation of glucose. Under the optimized detection potential, the sensor presented a chronoamperometric current response for the oxidation of glucose with two wide concentration ranges in PBS-diluted (62.80 to 180 µM and 305 to 8055 µM) and NaOH-diluted (58.90 to 117.6 µM and 180 to 10,055 µM) BP samples, which were within the limit of blood glucose levels of diabetic patients before (4.4-7.2 mM) and after (10 mM) meals (recommended by the American Diabetes Association). The sensor has a limit of detection of ca. 0.25 and 0.05 µM, respectively, and maximum sensitivity of ca. 36.55 and 1361.65 mA/cm2/mM, respectively, in PBS- and NaOH-diluted BP samples. The sensor also displayed excellent stability in the neutral and alkaline media due to the existence of hydrophobic linkers (2-ethyl imidazole) in the MAF-5-CoII NS, good repeatability and reproducibility, and interference-free signals. Thus, MAF-5-CoII NS is a promising nanozyme for the development of the disposable type of sensor for glucose detection in human body fluids. Graphical abstract.

Characterization of Inherently Chiral Electrosynthesized Oligomeric Films by Voltammetry and Scanning Electrochemical Microscopy (SECM).

A voltammetric and scanning electrochemical microscopy (SECM) investigation was performed on an inherently chiral oligomer-coated gold electrode to establish its general properties (i.e., conductivity and topography), as well as its ability to discriminate chiral electroactive probe molecules. The electroactive monomer (S)-2,2'-bis(2,2'-bithiophene-5-yl)-3,3'-bibenzothiophene ((S)-BT2T4) was employed as reagent to electrodeposit, by cyclic voltammetry, the inherently chiral oligomer film of (S)-BT2T4 (oligo-(S)-BT2T4) onto the Au electrode surface (resulting in oligo-(S)-BT2T4-Au). SECM measurements, performed in either feedback or competition mode, using the redox mediators [Fe(CN)6]4- and [Fe(CN)6]3- in aqueous solutions, and ferrocene (Fc), (S)-FcEA, (R)-FcEA and rac-FcEA (FcEA is N,N-dimethyl-1-ferrocenylethylamine) in CH3CN solutions, indicated that the oligomer film, as produced, was uncharged. The use of [Fe(CN)6]3- allowed establishing that the oligomer film behaved as a porous insulating membrane, presenting a rather rough surface. This was inferred from both the approach curves and linear and bidimensional SECM scans, which displayed negative feedback effects. The oligomer film acquired semiconducting or fully conducting properties when the Au electrode was biased at potential more positive than 0.6 V vs. Ag|AgCl|KCl. Under the latter conditions, the approach curves displayed positive feedback effects. SECM measurements, performed in competition mode, allowed verifying the discriminating ability of the oligo-(S)-BT2T4 film towards the (S)-FcEA and (R)-FcEA redox mediators, which confirmed the results obtained by cyclic voltammetry. SECM linear scans indicated that the enantiomeric discriminating ability of the oligo-(S)-BT2T4 was even across its entire surface.

Recent advances of electrochemical and optical enzyme-free glucose sensors operating at physiological conditions.

Diabetes is a pathological condition that requires the continuous monitoring of glucose level in the blood. Its control has been tremendously improved by the application of point-of-care devices. Conventional enzyme-based sensors with electrochemical and optical transduction systems can successfully measure the glucose concentration in human blood, but they suffer from the low stability of the enzyme. Non-enzymatic wearable electrochemical and optical sensors, with low-cost, high stability, point-of-care testing and online monitoring of glucose levels in biological fluids, have recently been developed and can help to manage and control diabetes worldwide. Advances in nanoscience and nanotechnology have enabled the development of novel nanomaterials that can be implemented for the use in enzyme-free systems to detect glucose. This review summarizes recent developments of enzyme-free electrochemical and optical glucose sensors, as well as their respective wearable and commercially available devices, capable of detecting glucose at physiological pH conditions without the need to pretreat the biological fluids. Additionally, the evolution of electrochemical glucose sensor technology and a couple of widely used optical detection systems along with the glucose detection mechanism is also discussed. Finally, this review addresses limitations and challenges of current non-enzymatic electrochemical, optical, and wearable glucose sensor technologies and highlights opportunities for future research directions.

Modified Screen Printed Electrode Suitable for Electrochemical Measurements in Gas Phase.

We describe a convenient assembly for screen printed carbon electrodes (SPCE) suitable for analyses in gaseous samples which are of course lacking in supporting electrolytes. It consists of a circular crown of filter paper, soaked in a RTIL or a DES, placed upon a disposable screen printed carbon cell, so as to contact the outer edge of the carbon disk working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL or DES and SPCE electrodes is assured by a gasket, and all components are installed in a polylactic acid holder. As a result of this configuration, a sensitive, fast-responding, membrane-free gas sensor is achieved where the real working electrode surface is the boundary zone of the carbon working disk contacted by the paper crown soaked in the polyelectrolyte. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of RTILs or DESs which are characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was evaluated by voltammetric and flow injection analyses of oxygen which was chosen as prototype of electroactive gaseous analytes. The results obtained pointed out that this assembly is very profitable for the analysis of gaseous atmospheres, especially when used as detector for FIA in gaseous streams.

A fast method for the detection of irinotecan in plasma samples by combining solid phase extraction and differential pulse voltammetry.

In this paper, a fast method for the detection of irinotecan (CPT-11) in plasma samples was investigated. CPT-11 is widely used in a number of chemotherapeutic treatments of several solid tumors. The method is based on the combination of a solid phase extraction and an electrochemical detection step. The extraction of CPT-11 from plasma was performed using solid phase extraction (SPE) columns and acetonitrile as eluent. The procedure included also a cleaning step to eliminate interference due to plasma endogenous compounds and the co-therapeutics 5-fluoroacil (5-FU) and folinic acid (FA). The latter are administered together with CPT-11 in the FOLFIRI regimen. The detection of CPT-11 was performed by differential pulse voltammetry at a glassy carbon electrode (GCE) in basified acetonitrile media. Under these conditions, a well-defined peak due to the oxidation of the tertiary ammine end of CPT-11, also free from interference due to main metabolites, was obtained. Calibration plots showed a good linear response with limit of detection and quantification of 1.10 × 10-7 and 3.74 × 10-7 M, respectively. The suitability of the method proposed here for clinical applications was verified by determining the concentration of CPT-11 in plasma samples of an oncological patient, collected after 30 and 180 min from the infusion of the drug. Graphical abstract.

Fast determination of extra-virgin olive oil acidity by voltammetry and Partial Least Squares regression.

In this paper, an approach for the detection of extra-virgin olive oil (EVOO) free-acidity, based on combination of voltammetric profiles (Voltammetry) and Partial Least Squares (PLS) multivariate regression, is described. Voltammetric measurements are performed with a 12.5 µm radius platinum microdisk, directly in the oil samples mixed with 0.5 M of the room temperature ionic liquid (RTIL) tri-hexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide, which acted as a supporting electrolyte, and allows achieving a suitable conductivity in the matrices. Multivariate regression is performed directly on full voltammetric responses recorded over a properly chosen negative potential range and scan rate, where essentially all free fatty acids, characterizing EVOOs, can be reproducibly reduced. PLS regression models are built by employing Italian EVOO samples training sets at different acidity levels (over the range 0.2% w/w - 1.5% w/w; (% w/w) represents mass percentage) and optimized by choosing the optimal complexity, in terms of number of latent variables (LVs). The free-acidity prediction is made through a multivariate model, constructed by using standards of known acidity (determined by the official volumetric titration method) and validated on an external sample set. To show the validity of the proposed method, the PLS/Voltammetry predictions of the free-acidity of a series of commercially available Italian EVOOs, ranging from 0.2 to 0.41 %w/w, are obtained and the values compared with those determined by the official titration approach. Differences found between the two methods are within 5% RSD.

Volatile aldehydes sensing in headspace using a room temperature ionic liquid-modified electrochemical microprobe.

The cyclic voltammetric behaviour of propionaldehyde (PA) and hexanaldehyde (HA), in 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTF2]), 1-butyl-3-methylimidazolium hydrogen sulphate ([BMIM][HSO4]) and 1-butyl-3-methylimidazolium hydroxide ([BMIM][OH]) was investigated at a platinum microelectrode. A clear oxidation process for both aldehydes was recorded only in [BMIM][OH]. On the basis of these evidences, an electrochemical microprobe (EMP), incorporating [BMIM][OH] as electrolyte, was assembled for sensing these aldehydes in gaseous phases. The EMP exposed in the headspace of the liquid aldehydes displayed voltammetric and amperometric responses, which depended on the aldehyde vapour pressures and, consequently, on the temperature employed. The usefulness of the [BMIM][OH] coated EMP for practical applications was assessed in the detection of HA vapour released from squalene (i.e., a lipid simulant matrix) samples spiked with known amounts of the aldehyde. Calibration plots were constructed at 40 °C, 50 °C and 60 °C, using both voltammetry and chronoamperometry. In both cases, good linearity between current and HA concentration in squalene was obtained over the range 3-300 ppm, with correlation coefficients higher than 0.991. Reproducibility, evaluated from at least three replicates, was within 5%. Detection limits, evaluated for a signal-to-noise ratio of 3, were in any case lower than 1.7 ppm. These analytical performances are suitable for monitoring VAs coming from lipid oxidation processes in food. An application concerning the determination of VAs in headspace of sunflower oil during an induced oxidative test to establish its thermal stability was also performed.

An extracellular polymeric substance quickly chelates mercury(II) with N-heterocyclic groups.

A strain of Klebsiella oxytoca DSM 29614 is grown on sodium citrate in the presence of 50 mg l-1 of Hg as Hg(NO3)2. During growth, the strain produces an extracellular polymeric substance (EPS), constituted by a mixture of proteins and a specific exopolysaccharide. The protein components, derived from the outer membrane of cells, are co-extracted with the extracellular exopolysaccharide using ethanol. The extracted EPS contains 7.5% of Hg (total amount). This indicates that EPS is an excellent material for the biosorption of Hg2+, through chemical complexation with the EPS components. The binding capacity of these species towards Hg2+ is studied by cyclic voltammetry, and Hg L3-edge XANES and EXAFS spectroscopy. The results found indicate that Hg2+ is mainly bound to the nitrogen of the imidazole ring or other N-heterocycle compounds. The hydroxyl moities of sugars and/or the carboxyl groups of two glucuronic acids in the polysaccharide can also play an important role in sequestring Hg2+ ions. However, N-heterocyclic groups of proteins bind Hg2+ faster than hydroxyl and carboxyl groups of the polysaccharide.

A broad mercury resistant strain of Pseudomonas putida secretes pyoverdine under limited iron conditions and high mercury concentrations.

The Pseudomonas putida FB1, known as a broad-spectrum mercury resistant strain, becomes yellow-green due to the secretion of pyoverdine (PVDs) under limited iron conditions and high mercury concentrations. Different modified Nelson's media were obtained by adding mercury, iron, and the complexing agent nitrilotriacetic acid to demonstrate that the strain produces only the highest concentrations of PVDs due to the induction with 25 µM Hg2+. An amount of 250 mg PVDs was purified from the supernatant of 1 litre culture. The various forms of PVDs were characterized using different techniques such as fluorescence spectroscopy, high performance liquid chromatography coupled with high resolution mass spectrometry, and scanning electron microscope equipped with energy dispersive X-ray analyser. A set of "in vivo" experiments demonstrated that additions of Hg2+ to the cultures from 10 to 25 µM Hg2+ stimulate an over secretion of PVDs suggesting that the toxic cation strongly reduces the availability of apo-PVDs, because the complex mercuric-pyoverdine is very stable at neutral pH, and hinder the formation of PVDs-Fe(III).

A novel electroanalytical approach based on the use of a room temperature ionic liquid for the determination of olive oil acidity.

In this paper, a novel voltammetric/amperometric approach for the direct determination of free acidity (FFA, expressed as mass percentage of free oleic acid) in olive oil samples is presented. The method is based on the reduction processes occurring at a platinum microdisk electrode involving the free fatty acids present in the matrices. To overcome problems related to the low conductivity of the samples investigated, olive oils were mixed with suitable amounts of the room temperature ionic liquid (RTIL), tri-hexyl(tetradecyl)phosphonium bis (trifluoromethylsulfonyl) imide ([P14,6,6,6]+[NTf2]-), which acted as a supporting electrolyte. Conditions for a reliable quantification of the acids were preliminarily investigated by performing voltammetric and chronoamperometric measurements in RTIL solutions containing oleic acid at different concentrations. Oleic acid (OA) was chosen as a model compound as it is the main component of the FFA content in olive oils. In order to establish the effect of oxygen on the electroanalytical responses, the reduction process of OA was investigated under both deoxygenated and oxygenated conditions. It was found that, in both situations, the current arising from the electrode process of OA depended linearly on the OA concentration over a wide range varying from 0.1% to 8% OA (w/w). This range includes FFA values which can be found on all categories of commercially available oil samples, including extra-virgin, virgin and lampante oils. Voltammetric and chronoamperometric experiments were also performed in oil/RTIL samples artificially acidified (extra-virgin olive oils with known addition of oleic acid) and in natural olive oils from some commercial categories. The results obtained indicated that the electrochemical procedure developed was satisfactory in terms of both sensitivity and detection limits. The reliability of the proposed approach for the detection of FFA was finally assessed by comparison of the voltammetric/chronoamperometric values with those obtained by the official method for quantification of olive oil acidity, which is an acid/base volumetric titration.

Polysaccharide-based silver nanoparticles synthesized by Klebsiella oxytoca DSM 29614 cause DNA fragmentation in E. coli cells.

Silver nanoparticles (AgNPs), embedded into a specific exopolysaccharide (EPS), were produced by Klebsiella oxytoca DSM 29614 by adding AgNO3 to the cultures during exponential growth phase. In particular, under aerobic or anaerobic conditions, two types of silver nanoparticles, named AgNPs-EPS(aer) and the AgNPs-EPS(anaer), were produced respectively. The effects on bacterial cells was demonstrated by using Escherichia coli K12 and Kocuria rhizophila ATCC 9341 (ex Micrococcus luteus) as Gram-negative and Gram-positive tester strains, respectively. The best antimicrobial activity was observed for AgNPs-EPS(aer), in terms of minimum inhibitory concentrations and minimum bactericidal concentrations. Observations by transmission electron microscopy showed that the cell morphology of both tester strains changed during the exposition to AgNPs-EPS(aer). In particular, an electron-dense wrapped filament was observed in E. coli cytoplasm after 3 h of AgNPs-EPS(aer) exposition, apparently due to silver accumulation in DNA, and both E. coli and K. rhizophila cells were lysed after 18 h of exposure to AgNPs-EPS(aer). The DNA breakage in E. coli cells was confirmed by the comparison of 3-D fluorescence spectra fingerprints of DNA. Finally the accumulation of silver on DNA of E. coli was confirmed directly by a significant Ag(+) release from DNA, using the scanning electrochemical microscopy and the voltammetric determinations.

Characterisation of biosynthesised silver nanoparticles by scanning electrochemical microscopy (SECM) and voltammetry.

Silver nanoparticles (AgNPs) were biosynthesised by a Klebsiella oxytoca strain BAS-10, which, during its growth, is known to produce a branched exopolysaccharide (EPS). Klebsiella oxytoca cultures, treated with AgNO3 and grown under either aerobic or anaerobic conditions, produced silver nanoparticles embedded in EPS (AgNPs-EPS) containing different amounts of Ag(0) and Ag(I) forms. The average size of the AgNPs-EPS was determined by transmission electron microscopy, while the relative abundance of Ag(0)- or Ag(I)-containing AgNPs-EPS was established by scanning electrochemical microscopy (SECM). Moreover, the release of silver(I) species from the various types of AgNPs-EPS was investigated by combining SECM with anodic stripping voltammetry. These measurements allowed obtaining information on the kinetic of silver ions release from AgNPs-EPS and their concentration profiles at the substrate/water interface.

Yttrium and lanthanide complexes of ß-dialdehydes: synthesis, characterization, luminescence and electrochemistry of coordination compounds with the conjugate base of bromomalonaldehyde.

Novel yttrium, europium and terbium coordination compounds having formulae [AsPh4][Ln(BrMA)4] (6LN), Ln(BrMA)3(bipyO2) (7Ln), Ln(NMA)3(phen) (8Ln) and Ln(NMA)3(terpy) (9Ln) (Ln = Y, Eu, Tb; BrMA = conjugate base of bromomalonaldehyde; bipyO2 = 2,2'-bipyridine-N,N'-dioxide; phen = 1,10-phenantroline; terpy = 2,2':6',2''-terpyridine) were synthesized and characterized by using spectroscopic and electrochemical techniques. Uncharged europium and, to a lesser extent, terbium complexes showed appreciable luminescence in the solid state upon excitation with UV light. Polymeric materials and ionic liquids containing BrMA and lanthanides were prepared and photoluminescence measurements were carried out. From an electrochemical point of view, europium(III) BrMA-complexes showed a quasi-reversible one-electron reduction process. The one electron transfer reaction Eu(III) to Eu(II) allowed the photoluminescence tuning of 8Eu deposited on the surface of a glassy carbon electrode.

A rapid electrochemical procedure for the detection of Hg(0) produced by mercuric-reductase: application for monitoring Hg-resistant bacteria activity.

In this work, gold microelectrodes are employed as traps for the detection of volatilized metallic mercury produced by mercuric reductase (MerA) extracted from an Hg-resistant Pseudomonas putida strain FB1. The enzymatic reduction of Hg (II) to Hg (0) was induced by NADPH cofactor added to the samples. The amount of Hg(0) accumulated on the gold microelectrode surface was determined by anodic stripping voltammetry (ASV) after transferring the gold microelectrode in an aqueous solution containing 0.1 M HNO(3) + 1 M KNO(3). Electrochemical measurements were combined with spectrofluorometric assays of NADPH consumption to derive an analytical expression for the detection of a relative MerA activity of different samples with respect to that of P. putida. The method developed here was employed for the rapid determination of MerA produced by bacteria harbored in soft tissues of clams (Ruditapes philippinarum), collected in high Hg polluted sediments of Northern Adriatic Sea in Italy.

In situ scanning electrochemical microscopy (SECM) detection of metal dissolution during zinc corrosion by means of mercury sphere-cap microelectrode tips.

This work presents a scanning electrochemical microscopy (SECM)-based in situ corrosion probing methodology that is capable of monitoring the release of zinc species in corrosion processes. It is based on the use of Hg-coated Pt microelectrodes as SECM tips, which offer a wider negative potential range than bare platinum or other noble-metal tips. This allows for the reduction of zinc ions at the tip to be investigated with low interference from hydrogen evolution and oxygen reduction from aqueous solutions. The processes involved in the corrosion of zinc during its immersion in chloride-containing solutions were successfully monitored by scanning the SECM tip, set at an adequate potential, across the sample either in one direction or in the X-Y plane parallel to its surface. In this way, it was possible to detect the anodic and cathodic sites at which the dissolution of zinc and the reduction of oxygen occurred, respectively. Additionally, cyclic voltammetry (CV) or constant potential measurements were used to monitor the release of zinc species collected at the tip during an SECM scan.

Tethered bilayer lipid micromembranes for single-channel recording: the role of adsorbed and partially fused lipid vesicles.

A mercury-supported bilayer lipid micromembrane was prepared by anchoring a thiolipid monolayer to a mercury cap electrodeposited on a platinum microdisc about 20 µm in diameter; a lipid monolayer was then self-assembled on top of the thiolipid monolayer either by vesicle fusion or by spilling a few drops of a lipid solution in chloroform on the cap and allowing the solvent to evaporate. Single-channel recording following incorporation of the alamethicin channel-forming peptide exhibits quite different features, depending on the procedure followed to form the distal lipid monolayer. The "spilling" procedure, which avoids the formation of adsorbed or partially fused vesicles, yields very sharp single-channel currents lasting only one or two milliseconds. These are ascribed to ionic flux into the hydrophilic spacer moiety of the thiolipid. Conversely, the vesicle-fusion procedure yields much longer single-channel openings analogous to those obtained with conventional bilayer lipid membranes, albeit smaller. This difference in behavior is explained by ascribing the latter single-channel currents to ionic flux into vesicles adsorbed and/or partially fused onto the tethered lipid bilayer, via capacitive coupling.