A highly sensitive electrochemical biosensor based on AuNP-modified gold electrodes for selective determination of serum levels of crosslaps.

This article explains a step-wise protocol to develop an electrochemical sensor to quantify serum levels of C-telopeptide (CTX) crosslinks also known as crosslaps in a matter of minutes and with high level of accuracy. The technique needs only one-step (incubation) and can thus be used for point of care screening. Due to the excellent electrical properties of the as-prepared immunosensor, CTX levels were successfully measured from 1 to 1000 pg/mL. This is while the normal reference of the marker is 50-450 pg/mL, suggesting that the sensor can acceptably detect CTX. The results also showed a good correlation with ECLIA in measuring serum levels of CTX.

SR-XRD in situ monitoring of copper-IUD corrosion in simulated uterine fluid using a portable spectroelectrochemical cell.

The objective of this work is to study the initial corrosion of copper in the presence of gold when placed in simulated uterine fluid in order to better understand the evolution of active components of copper-IUDs. In order to carry out this study, a portable cell was designed to partially simulate the uterine environment and provide a way of tracking the chemical changes occurring in the samples in situ within a controlled environment over a long period of time using synchrotron spectroelectrochemistry. The dynamically forming crystalline corrosion products are determined in situ for a range of copper-gold surface ratios over the course of a 10-day experiment in the cell. It is concluded that the insoluble deposits forming over this time are not the origin of the anticonception mechanism.

In-situ spectroelectrochemical characterization of the electrochemical growth and breakdown of a lead dodecanoate coating on a lead substrate.

This paper concerns a time lapse spectroelectrochemical study of the growth of lead dodecanoate layers on a lead substrate in an aqueous solution using cyclic voltammetry. In-situ synchrotron radiation X-ray diffraction measurements were carried out on station BM26A (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) in France. The diffraction pattern images were taken using a two-dimensional Mar CCD camera. After deposition of the coating, a spectroelectrochemical study of a linear sweep voltammetry experiment using an acetic acid electrolyte, simulating 'active' lead corrosion, was carried out on both a bare and lead dodecanoate coated sample. The results show that the coating inhibits the formation of new lead corrosion products.

Evaluation of an X-ray-excited optical microscope for chemical imaging of metal and other surfaces.

The application of a modular system for the nondestructive chemical imaging of metal and other surfaces is described using heritage metals as an example. The custom-built X-ray-excited optical luminescence (XEOL) microscope, XEOM 1, images the chemical state and short-range atomic order of the top 200 nm of both amorphous and crystalline surfaces. A broad X-ray beam is used to illuminate large areas (up to 4 mm(2)) of the sample, and the resulting XEOL emission is collected simultaneously for each pixel by a charge-coupled device sensor to form an image. The input X-ray energy is incremented across a range typical for the X-ray absorption near-edge structure (XANES) and an image collected for each increment. The use of large-footprint beams combined with parallel detection allows the power density to be kept low and facilitates complete nondestructive XANES mapping on a reasonable time scale. In this study the microscope was evaluated by imaging copper surfaces with well-defined patterns of different corrosion products (cuprite Cu2O and nantokite CuCl). The images obtained show chemical contrast, and filtering the XEOL light allowed different corrosion products to be imaged separately. Absorption spectra extracted from software-selected regions of interest exhibit characteristic XANES fingerprints for the compounds present. Moreover, when the X-ray absorption edge positions were extracted from each spectrum, an oxidation state map of the sample could be compiled. The results show that this method allows one to obtain nondestructive and noninvasive information at the micrometer scale while using full-field imaging.

Assessment of copper corrosion from frameless copper IUDs after long-term in utero residence.

OBJECTIVE: To assess the site-specific corrosive behavior of the frameless intrauterine device (IUD) following long-term exposure to the uterine environment. STUDY DESIGN: A qualitative and morphological study using X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS: Three GyneFix® IUDs that were in site up to 150 months were examined. In utero corroded copper sleeves were divided into 10 different groups based on their shape (U or O), orientation (inside or outside) and in utero residence time. XRD indicated the presence of solely cuprite (Cu2O) as corrosion product on both the inside and the outside of the copper sleeves, regardless of their shape. These results were confirmed by backscattered electron micrographs recorded on the inside, the outside and the cross-section of the IUD sleeve. SEM results suggest that shape and orientation slightly affect the corrosion rate. CONCLUSION: The apparent copper loss from both sides of GyneFix copper tubes proves that both sides are a potential copper source and therefore justifies the design of GyneFix IUD. This could be beneficial for women as the IUD could be reduced in size and therefore better tolerated. The impact on bleeding could also be minimized. IMPLICATION STATEMENT: Release of copper ions from both sides of the copper tubes of the frameless GyneFix® IUD allows the IUD to be reduced in size, contributing to better toleration. The impact on menstrual bleeding is also minimized by a smaller size of the foreign body.

Corrosion of Bronzes by Extended Wetting with Single versus Mixed Acidic Pollutants.

The corrosion of bronzes was examined in the context of single-acid versus mixed-acid (as in urban acid rain) solutions. Two bi-component bronzes (copper with either 3% Sn or 7% Sn) that closely represent those of historic artifacts were immersed for five weeks in conditions designed to replicate those experienced by statues and ornaments in cities where rainfall and humidity constantly produce an electrolyte layer on the surfaces of bronzes. Ions, acids, and particles of pollutants can dissolve in this layer, resulting in a variety of harsh corrosion processes. The kinetics of corrosion and the properties of the resulting patinas were monitored weekly by electrochemical impedance spectroscopy and open-circuit potential measurements. The sizes and appearances of the corrosion products were monitored and used to estimate the progress of the corrosion, whose crystalline structures were visualized using scanning electron microscopy with energy dispersive spectroscopy, identified by X-ray diffraction, and characterized by spectrocolorimetry. The electrochemical measurements demonstrated that greater damage (in terms of color change and corrosion product formation) did not correspond to deficiencies in protection. The mixed-acid solution did not corrode the bronzes, as would be expected from the additive effects of the single acids. The postulated mechanisms of metal dissolution appear to be specific to a particular bronze alloy, with the tin component playing an important role.

Real time observation of X-ray-induced surface modification using simultaneous XANES and XEOL-XANES.

In experiments preliminary to the design of an X-ray-excited optical luminescence (XEOL)-based chemical mapping tool we have used X-ray micro (4.5 × 5.2 µm) and macro (1 × 6 mm) beams with similar total fluxes to assess the effects of a high flux density beam of X-rays at energies close to an absorption edge on inorganic surfaces in air. The near surface composition of corroded cupreous alloys was analyzed using parallel X-ray and optical photoemission channels to collect X-ray absorption near-edge structure (XANES) data at the Cu K edge. The X-ray fluorescence channel is characteristic of the composition averages over several micrometers into the surface, whereas the optical channel is surface specific to about 200 nm. While the X-ray fluorescence data were mostly insensitive to the X-ray dose, the XEOL-XANES data from the microbeam showed significant dose-dependent changes to the superficial region, including surface cleaning, changes in the oxidation state of the copper, and destruction of surface compounds responsible for pre-edge fluorescence or phosphorescence in the visible. In one case, there was evidence that the lead phase in a bronze had melted. Conversely, data from the macrobeam were stable over several hours. Apart from localized heating effects, the microbeam damage is probably associated with the O3 loading of the surface and increased reaction rate with atmospheric water vapor.

Self assembled films of porphyrins with amine groups at different positions: influence of their orientation on the corrosion inhibition and the electrocatalytic activity.

Self-assembled molecular films of two cobalt porphyrins with amine groups at different positions-(5,10,15,20-tetrakis-(2-aminophenyl) porphyrin-cobalt(II), [Co(II) (T(o-NH(2))PP)] and (5,10,15,20-tetrakis-(4-aminophenyl) porphyrin-cobalt(II), [Co(II)(T(p-NH(2))PP)]-were formed on a gold substrate. The functionalized surfaces were characterized using Raman spectroscopy, atomic force microscopy and electrochemical methods. Both modified gold surfaces completely mask the charge transfer of a [Fe(CN)(6)](3-/4-) redox couple in solution, indicating the layer is highly resistive in behavior. Electrochemical impedance spectroscopy analyses revealed that the porphyrin film with amine groups at ortho positions shows a higher charge-transfer resistance with a better protective behavior compared to the para position modified surface. Raman, AFM and EIS data suggests that an ortho amine positioned molecule forms a more compact layer compared to the para-positioned molecule. This can be explained in terms of their orientation on the gold surface. [Co(II)(T(o-NH(2))PP)] adopted a saddle shape orientation whereas [Co(II)(T(p-NH(2))PP)] adopted a flat orientation on the gold surface. The porphyrin modified gold electrode catalyzes the oxygen reduction at lower potentials compared to the bare gold electrode. The shift in the overvoltage was higher in case of molecules with flat orientation compared to the saddle shaped oriented porphyrin molecules on the surface.

The use of synchrotron X-rays to observe copper corrosion in real time.

We have developed and tested two complementary methods for making time-lapse synchrotron X-ray diffraction (XRD) measurements of the growth of synthetic corrosion layers using a protocol for producing copper(I) chloride (nantokite), on copper as a test. In the first method, a copper coupon was spin-coated with saturated copper(II) chloride solution in air while the surface was characterized in real time using XRD with a fast one-dimensional (1-D) detector. In the second, a droplet of the same reagent was suspended from an X-ray-transparent window in a hermetically sealed cell and the coupon was brought into contact with this while XRD diffractograms were acquired with a charge-coupled device (CCD) camera. The protocol is completed by a deionized water rinse, which was also studied. The XRD shows nantokite precipitation in solution as well as growth on the surface, but the end products were variable proportions of nantokite, cuprite (Cu(2)O), and paratacamite (Cu(2)(OH)(3)Cl). The latter two were observed forming in a reaction between the nantokite and the rinsing water. Comparisons between samples analyzed in the synchrotron and at lower power densities show that the effects of any radiolysis or slight heating of the sample are insignificant in this case. It would be simple to extend these methods to other corrosion or surface reaction systems.

Electrochemical determination of hydrogen peroxide with cytochrome c peroxidase and horse heart cytochrome c entrapped in a gelatin hydrogel.

A novel and versatile method, based on a membrane-free enzyme electrode in which both the enzyme and a mediator protein are entrapped in a gelatine hydrogel was developed for the fabrication of biosensors. As a proof of principle, we prepared a hydrogen peroxide biosensor by successfully entrapping both horse heart cytochrome c (HHC) and Saccharomyces cerevisae cytochrome c peroxidase (CCP) in a gelatin matrix which is immobilized on a gold electrode. This electrode was first pretreated with 6-mercaptohexanol. The biosensor displayed a rapid response and an expanded linear response range from 0 to 0.3 mM (R = 0.987) with a detection limit of 1 × 10(-5)M in a HEPES buffer solution (pH 7.0). This method of encapsulation is now further investigated for industrial biosensor applications.

Development of a highly sensitive and robust Cor a 9 specific enzyme-linked immunosorbent assay for the detection of hazelnut traces.

Allergy to tree nuts represents an acute health problem. Sensitized people can be inadvertently exposed to hidden allergens resulting from cross-contamination of foods. For this reason, reliable and highly sensitive analytical methods are needed to be developed for control and labeling of food ingredients and products. In the present paper we have proposed a new allergen specific sandwich-ELISA for hazelnut operated in optical and electrochemical modes. The ELISA was based on chicken egg yolk antibodies raised against a major hazelnut allergen, Cor a 9. The developed ELISA has a limit of detection in phosphate buffer of 4 ng mL(-1). No significant cross-reactivity with peanut, wheat or other food ingredients has been detected. Extracts of blank control cookies did not show any false positive response and the limit of detection in cookies was estimated to be 0.1 µg of hazelnut protein per g of food (0.1 ppm). The ELISA protocol was successfully adapted to operate in electrochemical mode and it was applied for the detection of hazelnut traces in cookies.

Self-assembled supramolecular array of polymeric phthalocyanine on gold for the determination of hydrogen peroxide.

This Article describes for the first time the formation of a supramolecular self-assembled monolayer of polymeric phthalocyanine (poly(CuPc)) onto a gold substrate. The latter is established through the interaction of the cyano group, belonging to the poly(CuPc), with the metal substrate. The functionalized gold substrate was characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical methods. Results clearly demonstrated the interaction between gold and the nitrogen atom of cyano group and showed at the same time the formation of a completely covered polymeric monolayer on the gold surface. In addition, the modified gold surface seems to exhibit a reversible redox behavior and is found to act as an electronic conductor, which allows rapid electron transfer. Electrochemical impedance spectroscopy (EIS) analyses in the presence of [Fe(CN)(6)](3-/4-) as a redox couple revealed that the modified electrode showed a much lower electron transfer resistance compared with bare gold. In addition, the modified electrode is found to catalyze the H(2)O(2) reduction very effectively, showing a catalytic current that varies linearly with the peroxide concentration in the range of 0.35 to 70 µM with a detection limit of 0.25 µM.

Electrochemical study of gelatin as a matrix for the immobilization of horse heart cytochrome c.

The aim of this paper is to emphasize the strength of gelatin as a stable matrix for redox enzymes. Cyclic voltammetry has been applied for a detailed electrochemical study of horse heart cytochrome c (HHC) entrapped in a gelatin matrix immobilized on a gold electrode. The influence of the HHC concentration, the mass percentage of the gelatin and the nature of the gelatin on the electrochemical behaviour of HHC have been described in detail. In addition, attenuated total reflection infrared (ATR-IR) spectroscopy was used to prove the immobilization on a qualitative and conformational level. The thickness of the gelatin film was determined using a non-contact optical profiler. These results open up new perspectives in the development of stable, biocompatible matrices for redox enzymes. The latter has its relevance in the field of biosensor development.

The coordinated use of synchrotron spectroelectrochemistry for corrosion studies on heritage metals.

Corrosion is a major source of degradation in heritage metal objects, and any remedial measures are subject to a strong (Western) ethic that favors conservation as opposed to restoration. Accordingly, major scientific challenges exist for developing appropriate treatment methods to stabilize and protect artifacts after they are recovered from an archaeological site, both before and during their display or storage in a museum. Because inappropriate treatments can cause irreversible damage to irreplaceable objects, it is crucial that the chemical processes involved are fully understood and characterized before any preservation work is undertaken. In this regard, large infrastructural facilities such as synchrotrons, neutron sources, and particle accelerators provide a wealth of analytical possibilities, unavailable in smaller scale laboratories. In general, the intensity of the radiation available allows measurements on a short time scale or with high spatial resolution (or both), so heterogeneous changes induced by a chemical process can be recorded while they occur. The penetrative nature of the radiation (e.g., X-rays, protons, or neutrons) also allows a sample to be studied in air. If necessary, complete artifacts (such as paintings or statuettes) can be examined. In situ analysis in a controlled environment, such as a liquid or corrosive atmosphere, also becomes an exciting possibility. Finally, there are many complementary techniques (local atomic structure or crystal structure determination, macroscopic 3-D imaging (tomographies), imaging chemical analysis, and so on) so the many distinct details of a problem can be thoroughly explored. In this Account, we discuss the application of this general philosophy to studies of corrosion and its prevention in cultural heritage metals, focusing on our recent work on copper alloys. More specifically, we use synchrotron-based techniques to evaluate the use of corrosion potential measurements as a possible monitoring method for copper-based objects recovered from marine environments. The extraction of chlorides from such artifacts is a process that must take place before the artifacts are put on display or stored, because air exposure of untreated metal will result in severe damage or loss in as little as a few weeks. Chloride is removed by soaking the artifact for up to two years in tap water or dilute sodium sesquicarbonate, with regular solution changes. Our research supports the effectiveness of this treatment for thin nantokite (copper(I) chloride) layers, but it raises questions for copper hydroxychlorides (atacamite and paratacamite), especially when these minerals are trapped in fissures. Electrochemical parameters such as the corrosion potential are shown to be insensitive to the physical presence of large hydroxychloride coverages if they overlie a cuprite (Cu(2)O) layer. X-ray absorption spectroscopy proves to be a good monitor for the chloride in solution over the working electrode, whereas X-ray diffraction offers the potential for real-time measurement of the surface chloride composition. In principle, the two techniques together offer the possibility of monitoring surface and fluid levels simultaneously.

Optically detected X-ray absorption spectroscopy measurements as a means of monitoring corrosion layers on copper.

XANES and EXAFS information is conventionally measured in transmission through the energy-dependent absorption of X-rays or by observing X-ray fluorescence, but secondary fluorescence processes, such as the emission of electrons and optical photons (e.g., 200-1000 nm), can also be used as a carrier of the XAS signatures, providing complementary information such as improved surface specificity. Where the near-visible photons have a shorter range in a material, the data will be more surface specific. Moreover, optical radiation may escape more readily than X-rays through liquid in an environmental cell. Here, we describe a first test of optically detected X-ray absorption spectroscopy (ODXAS) for monitoring electrochemical treatments on copper-based alloys, for example, heritage metals. Artificially made corrosion products deposited on a copper substrate were analyzed in air and in a 1% (w/v) sodium sesquicarbonate solution to simulate typical conservation methods for copper-based objects recovered from marine environments. The measurements were made on stations 7.1 and 9.2 MF (SRS Daresbury, UK) using the mobile luminescence end station (MoLES), supplemented by XAS measurements taken on DUBBLE (BM26 A) at the ESRF. The ODXAS spectra usually contain fine structure similar to that of XAS spectra measured in X-ray fluorescence. Importantly, for the compounds examined, the ODXAS is significantly more surface specific, and >98% characteristic of thin surface layers of 0.5-1.5-microm thickness in cases where X-ray measurements are dominated by the substrate. However, EXAFS and XANES from broadband optical measurements are superimposed on a high background due to other optical emission modes. This produces statistical fluctuations up to double what would be expected from normal counting statistics because the data retain the absolute statistical fluctuation in the original raw count, while losing up to 70% of their magnitude when background is removed. The problem may be solved in future through optical filtering to isolate the information-containing band, combined with the use of higher input X-ray fluxes available on third-generation light sources.

Immobilization of cytochrome c on cysteamine-modified gold electrodes with EDC as coupling agent.

Cyclic voltammetry has been applied for the characterization of cross-linked horse heart cytochrome c (HHC) on cysteamine-modified gold electrodes. The cross-linking, i.e. amide bond formation, between the proteins was achieved by using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) as coupling reagent. The optimal conditions for the formation of the HHC film were determined by varying the HHC concentration. In addition the reproducibility, stability and the influence of the scan rate upon these films were investigated with cyclic voltammetry. The protein film stability in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer solution was tested by UV/vis absorption spectroscopy.

Ozonization and cyclic voltammetry as efficient methods for the regeneration of gelatin-coated SPR chips.

The application of ozonization and cyclic voltammetry for the regeneration of gold chips containing a chemisorbed gelatin layer is reported. The efficiency of the regeneration process was analyzed using various surface analysis techniques indicating a complete removal of the biopolymer layer. The current findings open up perspectives for regeneration and multiple application of gold chips for SPR measurements.

Comparison between the electrocatalytic properties of different metal ion phthalocyanines and porphyrins towards the oxidation of hydroxide.

This work reports on the electrocatalytic oxidation of hydroxide using different central metal ion phthalocyanines and porphyrins immobilized on gold electrodes. The apparent electrocatalytic activity of cobalt phthalocyanine or porphyrin modified electrodes was found to be the greatest among the present series of metal ion macrocycles investigated. Copper and unmetallated phthalocyanine or porphyrin modified electrodes show no electrocatalytic behaviour towards hydroxide, such as bare gold. A possible mechanism for the enhanced reactivity of cobalt ion macrocycles towards the oxygen evolution is given. It is also stated that the electrocatalytic activity towards an adsorbate involves several aspects, such as the coordination state of the central metal ion, the nature of the ligand, the stability of the complexes, the number of d electrons, the energy of orbitals and the strength of the bonding between the central metal ion and the axial ligand.

Assessment of the uncertainty budget for the amperometric measurement of dissolved oxygen.

This work aimed at identifying the main sources of uncertainty for the measurement of dissolved oxygen concentration in aqueous solutions. The experimental apparatus consists of an amperometric cell based on the Clark-type sensor. The corresponding uncertainty budget was assessed, this being a fundamental step for the validation of a measurement method. The principle of the measurement, as well as the procedure for the set-up and the characterisation of the cell, are described. The measurement equation was defined as a combination of Faraday's and Fick's laws, and a method was worked out for the empirical determination of the diffusivity parameter. In this connection, the solutions of oxygen were standardised by way of the Winkler's titration, as suggested by the ISO Guide 5813 and 5814. With this approach we aimed at contributing to the development of a potential primary method of measurement. A discussion of all the contributions to the overall uncertainty is reported, allowing operators to locate the largest ones and plan specific improvements.

Insights into electrolytic stabilization with weak polarization as treatment for archaeological copper objects.

Immersion of corroded copper artefacts in dilute sodium sesquicarbonate solution is a well-recognized stabilization technique--especially in the conservation of objects recovered from marine environments and therefore saturated with chlorides. Here we describe three linked experiments performed to investigate a variation on this treatment, involving the application of a low potential to the artefact in order to drive the chloride extraction process. This includes a new spectroelectrochemical approach which allows 2-D pseudorandom X-ray reflection diffraction patterns to be obtained without interrupting the reaction in solution. Experiments were carried out on synthetically produced chloride layers on copper (nantokite and atacamite). We show that a thick chloride layer is, in general, replaced by a thin cuprite layer through a mechanism which involves detachment of the chloride crystallites from the surface prior to dissolution.