Local pH Measurements Research Articles

Influence of Pulse Current Sequences and Organic Additives on pH Measured By Local Methods

Pulsed current with square waves are well-known to increase the properties of coatings obtained by electrodeposition. It was observed that either by periodically reversing the polarity of the current or by applying off times, deposits of improved properties can be observed [1]. This concerns for example a much finer grain size as well as reduction of hydrogen embrittlement. The strategy to be implemented for pulse parameters choice should be made carefully. If hydrogen discharge occurs only in case of limitation of metallic species diffusion, the study of transient curves (potential vs time as a response of a current pulse) highlighted the presence of a faradic range which allows the determination of the best cathodic parameters (pulse time and current density) as well as off-time duration. The situation where hydrogen discharge occurs at potentials less cathodic than the metallic species reduction makes it less straightforward. It is necessary to use reverse pulses, i.e. applying an anodic current during the pulses sequence, to obtain beneficial effects because they contribute to a rearrangement of the electrolyte layer close to the electrode [2]. For example, the reverse pulses lead to the double layer discharge, and counterbalance the effect of pH increase due to proton reduction during the electrolysis. This last phenomenon is detrimental for the electrochemical species present in complexed form, because it frequently results in a precipitation of hydroxides which will be included as contaminants in the coating. Thus, the measurement of local dependence of the pH at the electrode vicinity (around 100µm) is interesting, and was performed using micro-capillary pH electrodes (10µm inner diameter) [3]. After silanization, a capillary was filled with a buffer solution, except in its sharpened end, which was filled with an ionophore resin synthetized for this purpose and acting as a selective proton membrane. This pH electrode was fixed on the stage of a three-dimensional micromanipulator. Calibration of the pH electrode indicated a Nernstian response on a given pH range, systematically tested before and after each measurement. Local pH measurements in the vicinity of a steel electrode surface in unstirred conditions were performed during the relaxation phase after a polarization period of 1 min, in order to avoid any perturbation of the polarization on the potential of the pH electrode. The local pH was measured until the bulk pH value was reached. First results obtained with high yield electrolytes such as nickel or gold solutions confirm the dependence of the pH value with the modulation of current in pulsed mode and additives presence. [1] F. Lallemand, L. Ricq, E. Deschaseaux, L. De Vettor, P. Berçot, Electrodeposition of cobalt-iron alloys in pulsed current from electrolytes containing organic additives, Surf. Coat. Technol., 197 (2005) 10–17. [2] J. Rolet, M.P. Gigandet, S. Lallemand1, P. Bercot1, J.Y. Hihn; Effect of pulsed current parameters on the microstructure and properties of deposits for hard chromium electroplating from trivalent electrolytes (to be submitted) [3] A.Q. Vu, B. Vuillemin, R. Oltra, C. Allély; Cut-edge corrosion of a Zn–55Al-coated steel: A comparison between sulphate and chloride solutions, Corrosion Science 53 (2011) 3016–3025 Figure 1

In vitro antibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. Fourier transform infrared spectroscopy.

The metabolic response of Gram-positive Staphylococcus epidermidis (S. epidermidis) bacteria to bioceramic substrates was probed by means of Fourier transform infrared spectroscopy (FTIR). Oxide zirconia-toughened alumina (ZTA) and non-oxide silicon nitride (Si3N4) substrates were tested. Bacteria exposed to silica glass substrates were used as a control. S. epidermidis, a major cause of periprosthetic infections, was screened to obtain a precise time-lapse knowledge of its molecular composition and to mechanistically understand its interaction with different substrates. At the molecular level, the structure of proteins, lipids, nucleic acid, and aromatic amino acids evolved with time in response to different substrates. In combination with statistical validation and local pH measurements, a chemical lysis mechanism was spectroscopically observed in situ on the Si3N4 substrates. Utilization of FTIR in this study avoided fluorescence noise which occurred while probing the ZTA samples with Raman spectroscopy in a companion paper. The substrate-driven dynamics of polysaccharide and peptide variations in the bacterial cell wall, peculiar to Si3N4 bioceramics, are elucidated.

Local pH monitoring of small cluster of cells using a fiber-optic dual-core micro-probe

Biological studies of tissues and cells have enabled numerous discoveries, but these studies still bear potential risks of invalidation because of cell heterogeneity. Through high-accuracy techniques, recent studies have demonstrated that discrepancies do exist between the results from low-number-cell studies and cell-population-based results. Thus the urgent need to re-evaluate key principles on limited number of cells has been provoked. In this study, a novel designed dual-core fiber-optic pH micro-probe was fabricated and demonstrated for niche environment pH sensing with high spatial resolution. An organic-modified silicate (OrMoSils) sol-gel thin layer was functionalized by entrapping a pH indicator, 2′, 7′-Bis (2-carbonylethyl)-5(6)-carboxyfluorescein (BCECF), on a ∼70μm sized probe tip. Good linear correlation between fluorescence ratio of I560nm/I640nm and intercellular pH values was obtained within a biological-relevant pH range from 6.20 to 7.92 (R2=0.9834), and with a pH resolution of 0.035±0.005pH units. The probe’s horizontal spatial resolution was demonstrated to be less than 2mm. Moreover, the probe was evaluated by measuring the localized extracellular pH changes of cultured human lung cancer cells (A549) when exposed to titanium dioxide nanoparticles (TiO2 NPs). Results showed that the probe has superior capability for fast, local, and continual monitoring of a small cluster of cells, which provides researchers a fast and accurate technique to conduct local pH measurements for cell heterogeneity-related studies.

Localized Corrosion Behavior of AZ31B Magnesium Alloy with an Electrodeposited Poly(3,4-Ethylenedioxythiophene) Coating

Herein we report the characterization of localized corrosion of AZ31B magnesium alloy electrochemically coated with poly(3,4-ethylenedioxythiophene) (PEDOT) from ionic liquid electrolyte. Several scanning probe techniques including high resolution electron microscopy, SVET, SECM amperometric detection of H2 fluxes, potentiometric SECM detection of local pH and localized potentiodyanmic measurements were used to evaluate the microstructure of the coating and its corrosion protectiveness. In order to examine long-term durability of corrosion protection due to the PEDOT coating, these measurements were performed after different immersion times. It was observed that PEDOT coating appears to lose its protective ability after localized coverage of corrosion products. The results of this study provide important information considering the interest in this coating for use in biomedical implants and prior indications of beneficial passivation.

Stiffness-dependent in vitro uptake and lysosomal acidification of colloidal particles.

The physico-chemical properties of colloidal particles determine their uptake into cells. For a series of microparticles only one parameter, the mechanical stiffness, was varied, whereas other parameters such as size, shape, and charge were kept constant. The uptake was monitored in situ by analyzing individual particle trajectories including the progress of endocytosis, derived from local pH measurements around each particle. Evidence is presented that soft particles with low stiffness are transported faster to lysosomes than stiffer ones.

Local pH measurement at wet mineral-bacteria/air interface

Scanning electrochemical microscopy (SECM) was used to measure local pH in the thin water film located at the mineral-Rahnella aquatilis RA1/air interface. The method allowed differentiating acidification kinetics in conditions of natural soils and sediments where water can form film around mineral.

Local pH Measurement with Scanning Ion Conductance Microscopy

We report microscale pH probes and their application as a scanning probe in Scanning Ion Conductance Microscopy (SICM). Experiments are performed with electrodes that consist of a thin gold layer deposited on one side of a nanopipet. Subsequent insulation of the electrode with parylene and electropolymerization of aniline to form a polyaniline (PANi) thin film on the gold electrode surface creates a microscale pH probe with a dynamic range of pH 2.5–12 and sensitivity of 0.02 ΔpH. Porous membranes were examined with prepared electrodes. Ion current measured at the nanopipet opening served to control the position of the electrode with respect to the membrane surface and to report local conductance in the vicinity of the nanopipet, while local pH was measured by recording the potential difference between the PANi electrode and a reference electrode. Application of a transmembrane potential difference was utilized for additional control over migration across the membrane. Lateral resolution of the EMF response was studied with micrometer diameter pores. Additionally, the vertical resolution of the EMF response was studied as the pipet was lowered into the pores where a ΔpH of 0.13 was measured.

Optical molecular imaging detects changes in extracellular pH with the development of head and neck cancer

Noninvasive localized measurement of extracellular pH in cancer tissues can have a significant impact on the management of cancer. Despite its significance, there are limited approaches for rapid and noninvasive measurement of local pH in a clinical environment. In this study, we demonstrate the potential of noninvasive topical delivery of Alexa-647 labeled pHLIP (pH responsive peptide conjugated with Alexa Fluor(®) 647) to image changes in extracellular pH associated with head and neck squamous cell carcinoma using widefield and high resolution imaging. We report a series of preclinical analyses to evaluate the optical contrast achieved after topical delivery of Alexa-647 labeled pHLIP in intact fresh human tissue specimens using widefield and high-resolution fluorescence imaging. Using topical delivery, Alexa-647 labeled pHLIP can be rapidly delivered throughout the epithelium of intact tissues with a depth exceeding 700 µm. Following labeling with Alexa-647 labeled pHLIP, the mean fluorescent contrast increased four to eight fold higher in clinically abnormal tissues as compared to paired clinically normal biopsies. Furthermore, the imaging approach showed significant differences in fluorescence contrast between the cancer and the normal biopsies across diverse patients and different anatomical sites (unpaired comparison). The fluorescence contrast differences between clinically abnormal and normal tissues were in agreement with the pathologic evaluation. Topical application of fluorescently labeled pHLIP can detect and differentiate normal from cancerous tissues using both widefield and high resolution imaging. This technology will provide an effective tool to assess tumor margins during surgery and improve detection and prognosis of head and neck cancer.

M153R Mutation in a pH-Sensitive Green Fluorescent Protein Stabilizes Its Fusion Proteins

BackgroundGreen fluorescent protein (GFP) and its fusion proteins have been used extensively to monitor and analyze a wide range of biological processes. However, proteolytic cleavage often removes GFP from its fusion proteins, not only causing a poor signal-to-noise ratio of the fluorescent images but also leading to wrong interpretations.Methodology/Principal FindingsHere, we report that the M153R mutation in a ratiometric pH-sensitive GFP, pHluorin, significantly stabilizes its fusion products while the mutant protein still retaining a marked pH dependence of 410/470 nm excitation ratio of fluorescence intensity. The M153R mutation increases the brightness in vivo but does not affect the 410/470-nm excitation ratios at various pH values.Conclusions/SignificanceSince the pHluorin(M153R) probe can be directly fused to the target proteins, we suggest that it will be a potentially powerful tool for the measurement of local pH in living cells as well as for the analysis of subcellular localization of target proteins.

1K1324 細菌べん毛タンパク質輸送装置近傍の局所pHの測定(細胞生物的課題1,第49回日本生物物理学会年会)

1K1324 細菌べん毛タンパク質輸送装置近傍の局所pHの測定(細胞生物的課題1,第49回日本生物物理学会年会)

One-pot electrosynthesis of polyglycine-like thin film on platinum electrodes as transducer for solid state pH measurements

The anodic oxidation of concentrated glycine based aqueous electrolyte on smooth platinum electrode leads to a strongly grafted polyglycine-like coating on the surface in an irreversible way. Due to the proton affinity towards amino groups of polyglycine (PG), the electrodeposited thin film was used as receptor for solid potentiometric pH sensor. In order to reach local pH measurement, we developed miniaturized microelectrodes on glass substrate thanks to photolithography process. We used silver chloride on silver as the reference electrode. The couple (silver chloride, PG based platinum electrode) of microelectrodes gives linear potentiometric response vs. pH in the range [2–12], reversibly and with a sensitivity of 52.4 mV/pH (for 1 mm electrode size). PG based pH electrode is compared to other organic polymer based pH receptor such as linear polyethylenimine (L-PEI), polyaniline (PANI) and glass membrane.

On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers

This paper demonstrates local pH measurement in a microchip using a pH-sensing gel-microbead. To achieve this, the gel-microbead made of a hydrophilic photo-crosslinkable resin was functionalized with the pH indicator bromothymol blue (BTB). The primary constituent of this photo-crosslinkable resin is poly(ethylene glycol). Gel-microbeads impregnated with BTB were obtained by stirring the mixture solution, which was composed of the resin, BTB, and an electrolyte solution. The gel-microbead is polymerized by UV illumination. The polymerized gel-microbead can be manipulated by optical tweezers and made to adhere to a glass surface. The local pH was measured from the color of the gel-microbead impregnated with BTB by calibrated color information in the YCrCb color space. We succeeded in measuring the local pH value using the pH-sensing gel-microbead by manipulating and positioning it at the desired point in the microchip.

1P-164 高感度pHイメージングシステムを用いた細菌の細胞内局所pHの測定(分子モーター(1),第46回日本生物物理学会年会)

1P-164 高感度pHイメージングシステムを用いた細菌の細胞内局所pHの測定(分子モーター(1),第46回日本生物物理学会年会)

Reactant Concentrations from Fluorescence Correlation Spectroscopy with Tailored Fluorescent Probes. An Example of Local Calibration-Free pH Measurement

The present account is concerned with the measurement of local reactant concentrations by observing specific fluorescent probes in fluorescence correlation spectroscopy (FCS). The Theoretical Analysis section revisits the photophysical, thermodynamic, and kinetic information that is contained in the corresponding FCS correlation curves. In particular, we examine the conditions under which FCS is revealed as a superior tool to measure concentrations of reactive species. Careful molecular engineering of the specific fluorescent probes that simultaneously integrates photophysical, thermodynamic, and kinetic constraints will be required to benefit most from FCS. We illustrate the FCS titration approach with a series of fluorescent probes that we tailored to measure pH at around 4-6 by FCS after two-photon excitation. We show that an optimal design allows one to access pH without any preliminary calibrations such as the determination of the protonation constant or the photophysical properties of the fluorescent probe.

Study of conversion coatings obtained from tungstate-phosphoric acid solutions

Conversion coatings on zinc surfaces (Zn and electrogalvanized steel) were obtained with tungstate baths acidified by phosphoric acid under different experimental conditions. Open circuit potential and local pHs were monitored during the conversion processes. The conversion layers were submitted to immersion tests monitored by open circuit potential and electrochemical impedance spectroscopy. Scanning electron microscopy and energy dispersive X-ray complemented the electrochemical measures. The local pH measurements have evidenced that the conversing process occurs at a specific value of pH. Electrochemical impedance has detected similarities between the deterioration process of tungstate and chromate conversed zinc surfaces.

Investigation of concentration profiles inside operating biocatalytic sensors with scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) with amperometric or potentiometric measuring tips was used to investigate biocatalytic reactions inside the enzyme layer of a biosensor during its operation. The well known glucose oxidase catalyzed oxidation of glucose has been selected for the studies. Local, instantaneous concentration of dissolved oxygen and hydrogen peroxide was studied observing the amperometric current while miniaturized potentiometric tip served for local pH measurements. Liquid enzyme layer immobilized with Cellophane membrane or cross linked polyacrilamide gel membrane containing entrapped enzyme served for biocatalytic media in the SECM imaging. Local maximum of H 2O 2 and minimum of O 2 profiles were found at approximately 200 μm far from the substrate/enzyme layer boundary. From the experimental findings guidelines to design well functioning biocatalytic sensors could be concluded. The concentration profiles obtained with SECM techniques were compared with the results of simple model calculations carried out with the method of finite changes. Most of earlier made SECM studies dealing with enzyme reactions imaged the electrolyte being in contact with the immobilized enzyme. The data in our investigation, however, were collected inside the working catalytic layer.

Local pH Measurements during Pitting Corrosion at MnS Inclusions on Stainless Steel

microsensors were incorporated into a microcapillary cell to monitor changes simultaneously with electrochemical measurements. The microsensors were positioned at the center of the microcapillary cell tip opening and above the surface of the sample. During the dissolution of inclusions on AISI 304 stainless steel the of the nearby electrolyte decreased to a value close to 4 in . In , pitting corrosion occurred at inclusions, and the metastable and stable pitting events acidified the local environment. The metastable pits decreased the of the electrolyte to values between 2 and 4. The stable pits caused the of the electrolyte to decrease to ~2. ©2000 The Electrochemical Society

A sol–gel based fiber optic sensor for local blood pH measurements

This paper describes a fiber optic pH sensor based upon sol–gel encapsulation of a self-referencing dye, seminaphthorhodamine-1 carboxylate (SNARF-1C). The simple sol–gel fabrication procedure is ideal for encapsulation and immobilization of dye molecules onto the end of an optical fiber. A miniature bench-top fluorimeter system was developed for use with the optical fiber to obtain pH measurements. Linear and reproducible responses were obtained in human blood in the pH range 6.8–8.0, which encompasses the clinically-relevant range. The sensor was also shown to have low coating leachability. This sensor will be used as part of an array of sensors being developed to monitor stroke patients.