Ion Conductance

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Patrick R. Unwin - One of the best experts on this subject based on the ideXlab platform.

  • scanning Ion Conductance microscopy reveals differences in the Ionic environments of gram positive and negative bacteria
    Analytical Chemistry, 2020
    Co-Authors: Kelsey Cremin, Gabriel N Meloni, David Perry, Bryn A Jones, James Teahan, Christian Zerfass, Munehiro Asally, Orkun S Soyer, Patrick R. Unwin
    Abstract:

    This paper reports on the use of scanning Ion Conductance microscopy (SICM) to locally map the Ionic properties and charge environment of two live bacterial strains: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. SICM results find heterogeneities across the bacterial surface and significant differences among the Gram-positive and Gram-negative bacteria. The bioelectrical environment of the B. subtilis was found to be considerably more negatively charged compared to E. coli. SICM measurements, fitted to a simplified finite element method (FEM) model, revealed surface charge values of -80 to -140 mC m-2 for the Gram-negative E. coli. The Gram-positive B. subtilis show a much higher conductivity around the cell wall, and surface charge values between -350 and -450 mC m-2 were found using the same simplified model. SICM was also able to detect regIons of high negative charge near B. subtilis, not detected in the topographical SICM response and attributed to the extracellular polymeric substance. To further explore how the B. subtilis cell wall structure can influence the SICM current response, a more comprehensive FEM model, accounting for the physical properties of the Gram-positive cell wall, was developed. The new model provides a more realistic descriptIon of the cell wall and allows investigatIon of the relatIon between its key properties and SICM currents, building foundatIons to further investigate and improve understanding of the Gram-positive cellular microenvironment.

  • Scanning Ion Conductance Microscopy: Quantitative Nanopipette Delivery–Substrate Electrode CollectIon Measurements and Mapping
    2019
    Co-Authors: Baoping Chen, David Perry, Minkyung Kang, Ashley Page, Patrick R. Unwin
    Abstract:

    Scanning Ion Conductance microscopy (SICM) is becoming a powerful multifunctIonal tool for probing and analyzing surfaces and interfaces. This work outlines methodology for the quantitative controlled delivery of Ionic redox-active molecules from a nanopipette to a substrate electrode, with a high degree of spatial and temporal precisIon. Through control of the SICM bias applied between a quasi-reference counter electrode (QRCE) in the SICM nanopipette probe and a similar electrode in bulk solutIon, it is shown that Ionic redox species can be held inside the nanopipette, and then pulse-delivered to a defined regIon of a substrate positIoned beneath the nanopipette. A self-referencing hopping mode imaging protocol is implemented, where reagent is released in bulk solutIon (reference measurement) and near the substrate surface at each pixel in an image, with the tip and substrate currents measured throughout. Analysis of the tip and substrate current data provides an improved understanding of mass transport and nanoscale delivery in SICM and a new means of synchronously mapping electrode reactivity, surface topography, and charge. Experiments on Ru­(NH3)63+ reductIon to Ru­(NH3)62+ and dopamine oxidatIon in aqueous solutIon at a carbon fiber ultramicroelectrode (UME), used as the substrate, illustrate these aspects. Finite element method (FEM) modeling provides quantitative understanding of molecular delivery in SICM. The approach outlined constitutes a new methodology for electrode mapping and provides improved insights on the use of SICM for controlled delivery to interfaces generally

  • differential concentratIon scanning Ion Conductance microscopy
    Analytical Chemistry, 2017
    Co-Authors: David Perry, Ashley M Page, Baoping Chen, Bruno G Frenguelli, Patrick R. Unwin
    Abstract:

    Scanning Ion Conductance microscopy (SICM) is a nanopipette-based scanning probe microscopy technique that utilizes the Ionic current flowing between an electrode inserted inside a nanopipette probe containing electrolyte solutIon and a second electrode placed in a bulk electrolyte bath, to provide informatIon on a substrate of interest. For most applicatIons to date, the compositIon and concentratIon of the electrolyte inside and outside the nanopipette is identical, but it is shown herein that it can be very beneficial to lift this restrictIon. In particular, an Ionic concentratIon gradient at the end of the nanopipette, generates an Ionic current with a greatly reduced electric field strength, with particular benefits for live cell imaging. This differential concentratIon mode of SICM (ΔC-SICM) also enhances surface charge measurements and provides a new way to carry out reactIon mapping measurements at surfaces using the tip for simultaneous delivery and sensing of the reactIon rate. Comprehensive fin...

  • multifunctIonal scanning Ion Conductance microscopy
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2017
    Co-Authors: Ashley M Page, David Perry, Patrick R. Unwin
    Abstract:

    Scanning Ion Conductance microscopy (SICM) is a nanopipette-based technique that has traditIonally been used to image topography or to deliver species to an interface, particularly in a biological setting. This article highlights the recent blossoming of SICM into a technique with a much greater diversity of applicatIons and capability that can be used either standalone, with advanced control (potential–time) functIons, or in tandem with other methods. SICM can be used to elucidate functIonal informatIon about interfaces, such as surface charge density or electrochemical activity (Ion fluxes). Using a multi-barrel probe format, SICM-related techniques can be employed to deposit nanoscale three-dimensIonal structures and further functIonality is realized when SICM is combined with scanning electrochemical microscopy (SECM), with simultaneous measurements from a single probe opening up considerable prospects for multifunctIonal imaging. SICM studies are greatly enhanced by finite-element method modelling for quantitative treatment of issues such as resolutIon, surface charge and (tip) geometry effects. SICM is particularly applicable to the study of living systems, notably single cells, although applicatIons extend to materials characterizatIon and to new methods of printing and nanofabricatIon. A more thorough understanding of the electrochemical principles and properties of SICM provides a foundatIon for significant applicatIons of SICM in electrochemistry and interfacial science.

  • quantitative visualizatIon of molecular delivery and uptake at living cells with self referencing scanning Ion Conductance microscopy scanning electrochemical microscopy
    Analytical Chemistry, 2017
    Co-Authors: Ashley M Page, David Perry, Minkyung Kang, Alexander Armitstead, Patrick R. Unwin
    Abstract:

    A multifunctIonal dual-channel scanning probe nanopipet that enables simultaneous scanning Ion Conductance microscopy (SICM) and scanning electrochemical microscopy (SECM) measurements is demonstrated to have powerful new capabilities for spatially mapping the uptake of molecules of interest at living cells. One barrel of the probe is filled with electrolyte and the molecules of interest and is open to the bulk solutIon for both topographical feedback and local delivery to a target interface, while a solid carbon electrode in the other barrel measures the local concentratIon and flux of the delivered molecules. This setup allows differentiatIon in molecular uptake rate across several regIons of single cells with individual measurements at nanoscale resolutIon. Further, operating in a “hopping mode”, where the probe is translated toward the interface (cell) at each point allows self-referencing to be employed, in which the carbon electrode response is calibrated at each and every pixel in bulk for comparis...

Tilman E. Schäffer - One of the best experts on this subject based on the ideXlab platform.

  • high speed scanning Ion Conductance microscopy for sub second topography imaging of live cells
    Nanoscale, 2019
    Co-Authors: Stefan Simeonov, Tilman E. Schäffer
    Abstract:

    Scanning Ion Conductance microscopy (SICM) is an emerging tool for non-invasive and high-resolutIon topography imaging of live cells. However, the imaging speed of conventIonal SICM setups is slow, requiring several seconds or even minutes per image, thereby making it difficult to study cellular dynamics. Here, we describe a high-speed SICM (HS-SICM) setup for topography imaging in the hopping mode with a pixel rate of 11.0 kHz, which is 15 times faster than what was reported before. In combinatIon with a “turn step” procedure for rapid pipette retractIon, we image the ultra-fast morphodynamics of live human platelets, A6 cells, and U2OS cells at a rate as fast as 0.6 s per frame. The results show that HS-SICM provides a useful platform for investigating the dynamics of cell morphology on a sub-second timescale.

  • thrombin induced cytoskeleton dynamics in spread human platelets observed with fast scanning Ion Conductance microscopy
    Scientific Reports, 2017
    Co-Authors: Jan Seifert, Johannes Rheinlaender, Florian Lang, Meinrad Gawaz, Tilman E. Schäffer
    Abstract:

    Platelets are small anucleate blood cells involved in haemostasis. Platelet activatIon, caused by agonists such as thrombin or by contact with the extracellular matrix, leads to platelet adhesIon, aggregatIon, and coagulatIon. Activated platelets undergo shape changes, adhere, and spread at the site of injury to form a blood clot. We investigated the morphology and morphological dynamics of human platelets after complete spreading using fast scanning Ion Conductance microscopy (SICM). In contrast to unstimulated platelets, thrombin-stimulated platelets showed increased morphological activity after spreading and exhibited dynamic morphological changes in the form of wave-like movements of the lamellipodium and dynamic protrusIons on the platelet body. The increase in morphological activity was dependent on thrombin concentratIon. No increase in activity was observed following exposure to other activatIon agonists or during contact-induced activatIon. InhibitIon of actin polymerizatIon and inhibitIon of dynein significantly decreased the activity of thrombin-stimulated platelets. Our data suggest that these morphological dynamics after spreading are thrombin-specific and might play a role in coagulatIon and blood clot formatIon.

  • comparative morphology analysis of live blood platelets using scanning Ion Conductance and robotic dark field microscopy
    Platelets, 2016
    Co-Authors: Maxjoseph Kraus, Tilman E. Schäffer, Jan Seifert, Meinrad Gawaz, Erwin F Strasser, Johannes Rheinlaender
    Abstract:

    AbstractMany conventIonal microscopy techniques for investigating platelet morphology such as electron or fluorescence microscopy require highly invasive treatment of the platelets such as fixatIon, drying and metal coating or staining. Here, we present two unique but entirely different microscopy techniques for direct morphology analysis of live, unstained platelets: scanning Ion Conductance microscopy (SICM) and robotic dark-field microscopy (RDM). We demonstrate that both techniques allow for a quantitative evaluatIon of the morphological features of live adherent platelets. We show that their morphology can be quantified by both techniques using the same geometric parameters and therefore can be directly compared. By imaging the same identical platelets subsequently with SICM and RDM, we found that area, perimeter and circularity of the platelets are directly correlated between SICM and dark-field microscopy (DM), while the fractal dimensIon (FD) differed between the two microscopy techniques. We show...

  • Lateral ResolutIon and Image FormatIon in Scanning Ion Conductance Microscopy.
    Analytical chemistry, 2015
    Co-Authors: Johannes Rheinlaender, Tilman E. Schäffer
    Abstract:

    The scanning Ion Conductance microscope (SICM) is a powerful tool for imaging the topography of soft samples in an aqueous environment. Despite the rising popularity of the SICM, the image formatIon process and the fundamental limit of the lateral resolutIon are still a matter of debate. Using microfabricated samples, we investigated the imaging of small cylindrical particles, elongated objects, and topography steps and present the first direct comparison of numerical and experimental data. For the lateral resolutIon we considered two alternative definitIons: the distance at which two small particles can clearly be resolved from each other in an image, and the apparent full width at half-maximum of small particles. For both definitIons, we found a lateral resolutIon of about 3 times the inner opening radius of the pipet. We further validated this resolutIon limit in measurements on supported lipid bilayers and a polycarbonate sample using pipets with opening radii down to 8 nm.

  • comparison of atomic force microscopy and scanning Ion Conductance microscopy for live cell imaging
    Langmuir, 2015
    Co-Authors: Jan Seifert, Pavel Novák, Johannes Rheinlaender, Yuri E. Korchev, Tilman E. Schäffer
    Abstract:

    Atomic force microscopy (AFM) and scanning Ion Conductance microscopy (SICM) are excellent and commonly used techniques for imaging the topography of living cells with high resolutIon. We present a direct comparison of AFM and SICM for imaging microvilli, which are small features on the surface of living cells, and for imaging the shape of whole cells. The imaging quality on microvilli increased significantly after cell fixatIon for AFM, whereas for SICM it remained constant. The apparent shape of whole cells in the case of AFM depended on the imaging force, which deformed the cell. In the case of SICM, cell deformatIons were avoided, owing to the contact-free imaging mechanism. We estimated that the lateral resolutIon on living cells is limited by the cell’s elastic modulus for AFM, while it is not for SICM. By long-term, time-lapse imaging of microvilli dynamics, we showed that the imaging quality decreased with time for AFM, while it remained constant for SICM.

Yuri E. Korchev - One of the best experts on this subject based on the ideXlab platform.

  • nanoscale imaging of primary cilia with scanning Ion Conductance microscopy
    Analytical Chemistry, 2018
    Co-Authors: Yuanshu Zhou, Pavel Novák, Yuri E. Korchev, Andrew Shevchuk, Masaki Saito, Takafumi Miyamoto, Takeshi Fukuma, Yasufumi Takahashi
    Abstract:

    Primary cilia are hair-like sensory organelles whose dimensIons and locatIon vary with cell type and culture conditIon. Herein, we employed scanning Ion Conductance microscopy (SICM) to visualize the topography of primary cilia from different cell types. By combining SICM with fluorescence imaging, we successfully distinguished between surface cilia that project outward from the cell surface and subsurface cilia that are trapped below it. The nanoscale structure of the ciliary pocket, which cannot be easily identified using a confocal fluorescence microscope, was observed in SICM images. Furthermore, we developed a topographic reconstructIon method using current-distance profiles to evaluate the relatIonship between set point and topographic image and found that a low set point is important for detecting the true topography of a primary cilium using hopping mode SICM.

  • adaptive hopping probe Ion Conductance microscopy of live cells at 5 10 nm resolutIon
    Biophysical Journal, 2016
    Co-Authors: Catalina A Velezortega, Pavel Novák, Yuri E. Korchev, Oleg Belov, Samir A Rawashdeh, Gregory I Frolenkov
    Abstract:

    The inherent low imaging speed of hopping probe Ion Conductance microscopy (HPICM) poses a constraint for the study of living cells at super resolutIon. The duratIon of each imaging frame further increases when the cell topography requires large approach/retractIon movements of the scanning pipette. We have modified our HPICM system to increase its imaging speed and sensitivity.We replaced the Z-scanner with a ∼18 kHz resonant frequency piezo assembly to allow for faster pipette movements. An external proportIonal-integral-derivative controller was used to decrease the delay in the Z-scanner. In our modified HPICM algorithm the approach speed adapts to the changes in the Ionic current flowing through the pipette. Altogether, our changes to the HPICM system allowed for approach speeds up to 4X faster with delays of only ∼50μs. Our “adaptive” approach curve effectively reduced the noise floor by half, which improved the vertical resolutIon of the system to ∼5nm. We also introduced adaptive filtering of the Ionic current, which decreased by half the minimum setpoint, thus improving the system's sensitivity.To test the performance of the improved HPICM setup, we imaged the vertically protruding stereocilia (∼0.5-3μm in height, ∼100-400nm in diameter) of the rat inner ear sensory cells. When we previously imaged these structures with HPICM, we used glutaraldehyde-fixed cells and each imaging frame took >44 min (Novak et al. Nat Methods, 2009). Now, the entire stereocilia bundle (∼9x9μm) in a live cell is imaged in ∼15 min and sub-regIons of interest (∼2x2μm) in ∼3-6 min, with ∼10-30nm XY resolutIon, even with the hop amplitudes of 3-5μm.Our improved HPICM system allows for the faster imaging of live cells at nanometer resolutIon, even in the cells with very convoluted topographies.Supported by NIDCD/NIH (R01DC008861, R01DC014658).

  • comparison of atomic force microscopy and scanning Ion Conductance microscopy for live cell imaging
    Langmuir, 2015
    Co-Authors: Jan Seifert, Pavel Novák, Johannes Rheinlaender, Yuri E. Korchev, Tilman E. Schäffer
    Abstract:

    Atomic force microscopy (AFM) and scanning Ion Conductance microscopy (SICM) are excellent and commonly used techniques for imaging the topography of living cells with high resolutIon. We present a direct comparison of AFM and SICM for imaging microvilli, which are small features on the surface of living cells, and for imaging the shape of whole cells. The imaging quality on microvilli increased significantly after cell fixatIon for AFM, whereas for SICM it remained constant. The apparent shape of whole cells in the case of AFM depended on the imaging force, which deformed the cell. In the case of SICM, cell deformatIons were avoided, owing to the contact-free imaging mechanism. We estimated that the lateral resolutIon on living cells is limited by the cell’s elastic modulus for AFM, while it is not for SICM. By long-term, time-lapse imaging of microvilli dynamics, we showed that the imaging quality decreased with time for AFM, while it remained constant for SICM.

  • imaging single nanoparticle interactIons with human lung cells using fast Ion Conductance microscopy
    Nano Letters, 2014
    Co-Authors: Pavel Novák, Max J. Lab, Julia Gorelik, Andrew Shevchuk, David Klenerman, Pakatip Ruenraroengsak, Michele Miragoli, Andrew J Thorley, Teresa D Tetley, Yuri E. Korchev
    Abstract:

    Experimental data on dynamic interactIons between individual nanoparticles and membrane processes at nanoscale, essential for biomedical applicatIons of nanoparticles, remain scarce due to limitatIons of imaging techniques. We were able to follow single 200 nm carboxyl-modified particles interacting with identified membrane structures at the rate of 15 s/frame using a scanning Ion Conductance microscope modified for simultaneous high-speed topographical and fluorescence imaging. The imaging approach demonstrated here opens a new window into the complexity of nanoparticle–cell interactIons.

  • Combined Ion Conductance and fluorescence confocal microscopy for biological cell membrane transport studies
    Journal of Optics, 2013
    Co-Authors: Andriy Shevchuk, Pavel Novák, Martin Nuñez Velazquez, Tom P. Fleming, Yuri E. Korchev
    Abstract:

    Optical visualizatIon of nanoscale morphological changes taking place in living biological cells during such important processes as endo- and exocytosis is challenging due to the low refractive index of lipid membranes. In this paper we summarize and discuss advances in the powerful combinatIon of two complementary live imaging techniques, Ion Conductance and fluorescence confocal microscopy, that allows cell membrane topography to be related with molecular-specific fluorescence at high spatial and temporal resolutIon. We demonstrate the feasibility of the use of Ion Conductance microscopy to image apical plasma membrane of mouse embryo trophoblast outgrowth cells at a resolutIon sufficient to depict single endocytic pits. This opens the possibility to study individual endocytic events in embryo trophoblast outgrowth cells where endocytosis plays a crucial role during early stages of embryo development.

Lane A Baker - One of the best experts on this subject based on the ideXlab platform.

  • scanning Ion Conductance microscopy
    Chemical Reviews, 2021
    Co-Authors: Cheng Zhu, Kaixiang Huang, Natasha P Siepser, Lane A Baker
    Abstract:

    Scanning Ion Conductance microscopy (SICM) has emerged as a versatile tool for studies of interfaces in biology and materials science with notable utility in biophysical and electrochemical measurements. The heart of the SICM is a nanometer-scale electrolyte filled glass pipette that serves as a scanning probe. In the initial conceptIon, manipulatIons of Ion currents through the tip of the pipette and appropriate positIoning hardware provided a route to recording micro- and nanoscopic mapping of the topography of surfaces. Subsequent advances in instrumentatIon, probe design, and methods significantly increased opportunities for SICM beyond recording topography. HybridizatIon of SICM with coincident characterizatIon techniques such as optical microscopy and faradaic electrodes have brought SICM to the forefront as a tool for nanoscale chemical measurement for a wide range of applicatIons. Modern approaches to SICM realize an important tool in analytical, bioanalytical, biophysical, and materials measurements, where significant opportunities remain for further exploratIon. In this review, we chronicle the development of SICM from the perspective of both the development of instrumentatIon and methods and the breadth of measurements performed.

  • characterizatIon of membrane patch Ion channel probes for scanning Ion Conductance microscopy
    Small, 2018
    Co-Authors: Yuhan Zeng, Yucheng Xiao, Theodore R Cummins, Lane A Baker
    Abstract:

    : IntegratIon of dual-barrel membrane patch-Ion channel probes (MP-ICPs) to scanning Ion Conductance microscopy (SICM) holds promise of providing a revolutIonized approach of spatially resolved chemical sensing. A series of experiments are performed to further the understanding of the system and to answer some fundamental questIons, in preparatIon for future developments of this approach. First, MP-ICPs are constructed that contain different types of Ion channels including transient receptor potential vanilloid 1 and large Conductance Ca2+ -activated K+ channels to establish the generalizability of the methods. Next, the capability of the MP-ICP platforms in single Ion channel activity measurements is proved. In additIon, the interplay between the SICM barrel and the ICP barrel is studied. For Ion channels gated by uncharged ligands, channel activity at the ICP barrel is unaffected by the SICM barrel potential; whereas for Ion channels that are gated by charged ligands, enhanced channel activity can be obtained by biasing the SICM barrel at potentials with opposite polarity to the charge of the ligand molecules. Finally, a proof-of-principle experiment is performed and site-specific molecular/Ionic flux sensing is demonstrated at single-Ion-channel level, which show that the MP-ICP platform can be used to quantify local molecular/Ionic concentratIons.

  • membrane patches as Ion channel probes for scanning Ion Conductance microscopy
    Faraday Discussions, 2016
    Co-Authors: Wenqing Shi, Yuhan Zeng, Yucheng Xiao, Theodore R Cummins, Lushan Zhou, Lane A Baker
    Abstract:

    We describe dual-barrel Ion channel probes (ICPs), which consist of an open barrel and a barrel with a membrane patch directly excised from a donor cell. When incorporated with scanning Ion Conductance microscopy (SICM), the open barrel (SICM barrel) serves to measure the distance-dependent Ion current for non-invasive imaging and positIoning of the probe in the same fashIon of traditIonal SICM. The second barrel with the membrane patch supports Ion channels of interest and was used to investigate Ion channel activities. To demonstrate robust probe control with the dual-barrel ICP-SICM probe and verify that the two barrels are independently addressable, current–distance characteristics (approach curves) were obtained with the SICM barrel and simultaneous, current–time (I–T) traces were recorded with the ICP barrel. To study the influence that the distance between ligand-gated Ion channels (i.e., large Conductance Ca2+-activated K+ channels/BK channels) and the ligand source (i.e., Ca2+ source) has on channel activatIons, Ion channel activities were recorded at two fixed probe–substrate distances (Dps) with the ICP barrel. The two fixed positIons were determined from approach curves acquired with the SICM barrel. One positIon was defined as the “In-control” positIon, where the probe was in close proximity to the ligand source; the second positIon was defined as the “Far” positIon, where the probe was retracted far away from the ligand source. Our results confirm that channel activities increased dramatically with respect to both open channel probability and single channel current when the probe was near the ligand source, as opposed to when the probe was far away from the ligand source.

  • Capturing Rare Conductance in Epithelia with Potentiometric-Scanning Ion Conductance Microscopy.
    Analytical chemistry, 2016
    Co-Authors: Lushan Zhou, Jianghui Hou, Yongfeng Gong, Abby Sunq, Lane A Baker
    Abstract:

    Tight junctIons (TJs) are barrier forming structures of epithelia and can be described as tightly sealed intercellular spaces. Transport properties have been extensively studied for bicellular TJs (bTJs). Knowledge of the barrier functIons of tricellular junctIons (tTJs) are less well understood, due largely to a lack of proper techniques to locally measure discrete tTJ properties within a much larger area of epithelium. In this study, we use a nanoscale pipet to precisely locate tTJs within epithelia and measure the apparent local Conductance of tTJs with a technique termed potentiometric scanning Ion Conductance microscopy (P-SICM). P-SICM shows the ability to differentiate transport through tTJs and bTJs, which was not possible with previous techniques and assays. We describe P-SICM investigatIons of both wild type and tricellulin overexpressIon Madin-Darby Canine Kidney (strain II, MDCKII) cells.

  • Capturing Rare Conductance in Epithelia with Potentiometric-Scanning Ion Conductance Microscopy
    2016
    Co-Authors: Lushan Zhou, Jianghui Hou, Yongfeng Gong, Abby Sunq, Lane A Baker
    Abstract:

    Tight junctIons (TJs) are barrier forming structures of epithelia and can be described as tightly sealed intercellular spaces. Transport properties have been extensively studied for bicellular TJs (bTJs). Knowledge of the barrier functIons of tricellular junctIons (tTJs) are less well understood, due largely to a lack of proper techniques to locally measure discrete tTJ properties within a much larger area of epithelium. In this study, we use a nanoscale pipet to precisely locate tTJs within epithelia and measure the apparent local Conductance of tTJs with a technique termed potentiometric scanning Ion Conductance microscopy (P-SICM). P-SICM shows the ability to differentiate transport through tTJs and bTJs, which was not possible with previous techniques and assays. We describe P-SICM investigatIons of both wild type and tricellulin overexpressIon Madin-Darby Canine Kidney (strain II, MDCKII) cells

Kim Mckelvey - One of the best experts on this subject based on the ideXlab platform.

  • simultaneous interfacial reactivity and topography mapping with scanning Ion Conductance microscopy
    Analytical Chemistry, 2016
    Co-Authors: Dmitry Momotenko, Kim Mckelvey, Minkyung Kang, Gabriel N Meloni, Patrick R. Unwin
    Abstract:

    Scanning Ion Conductance microscopy (SICM) is a powerful technique for imaging the topography of a wide range of materials and interfaces. In this report, we develop the use and scope of SICM, showing how it can be used for mapping spatial distributIons of Ionic fluxes due to (electro)chemical reactIons occurring at interfaces. The basic idea is that there is a change of Ion Conductance inside a nanopipet probe when it approaches an active site, where the Ionic compositIon is different to that in bulk solutIon, and this can be sensed via the current flow in the nanopipet with an applied bias. Careful tuning of the tip potential allows the current response to be sensitive to either topography or activity, if desired. Furthermore, the use of a distance modulatIon SICM scheme allows reasonably faithful probe positIoning using the resulting ac response, irrespective of whether there is a reactIon at the interface that changes the local Ionic compositIon. Both strategies (distance modulatIon or tuned bias) all...

  • quad barrel multifunctIonal electrochemical and Ion Conductance probe for voltammetric analysis and imaging
    Analytical Chemistry, 2015
    Co-Authors: Binoy Paulose Nadappuram, Aleix G. Güell, Kim Mckelvey, Joshua C Byers, Alex W Colburn, Robert A Lazenby, Patrick R. Unwin
    Abstract:

    The fabricatIon and use of a multifunctIonal electrochemical probe incorporating two independent carbon working electrodes and two electrolyte-filled barrels, equipped with quasi-reference counter electrodes (QRCEs), in the end of a tapered micrometer-scale pipet is described. This “quad-probe” (4-channel probe) was fabricated by depositing carbon pyrolytically into two diagonally opposite barrels of a laser-pulled quartz quadruple-barrelled pipet. After filling the open channels with electrolyte solutIon, a meniscus forms at the end of the probe and covers the two working electrodes. The two carbon electrodes can be used to drive local electrochemical reactIons within the meniscus while a bias between the QRCEs in the electrolyte channels provides an Ion Conductance signal that is used to control and positIon the meniscus on a surface of interest. When brought into contact with a surface, localized high resolutIon amperometric imaging can be achieved with the two carbon working electrodes with a spatial ...

  • bias modulated scanning Ion Conductance microscopy
    Analytical Chemistry, 2014
    Co-Authors: Kim Mckelvey, David Perry, Joshua C Byers, Alex W Colburn, Patrick R. Unwin
    Abstract:

    Nanopipets are versatile tools for nanoscience, particularly when used in scanning Ion Conductance microscopy (SICM) to determine, in a noncontact manner, the topography of a sample. We present a new method, applying an oscillating bias between a quasi-reference counter electrode (QRCE) in the SICM nanopipet probe and a second QRCE in the bulk solutIon, to generate a feedback signal to control the distance between the end of a nanopipet and a surface. Both the amplitude and phase of the oscillating Ion current, induced by the oscillating bias and extracted using a phase-sensitive detector, are shown to be sensitive to the probe–surface distance and are used to provide stable feedback signals. The phase signal is particularly sensitive at high frequencies of the oscillating bias (up to 30 kHz herein). This development eliminates the need to physically oscillate the probe to generate an oscillating Ion current feedback signal, as needed for conventIonal SICM modes. Moreover, bias modulatIon allows a feedbac...

  • fabricatIon and characterizatIon of dual functIon nanoscale ph scanning Ion Conductance microscopy sicm probes for high resolutIon ph mapping
    Analytical Chemistry, 2013
    Co-Authors: Binoy Paulose Nadappuram, Kim Mckelvey, Alex W Colburn, Rehab Al Botros, Patrick R. Unwin
    Abstract:

    The easy fabricatIon and use of nanoscale dual functIon pH-scanning Ion Conductance microscopy (SICM) probes is reported. These probes incorporate an iridium oxide coated carbon electrode for pH measurement and an SICM barrel for distance control, enabling simultaneous pH and topography mapping. These pH-SICM probes were fabricated rapidly from laser pulled theta quartz pipets, with the pH electrode prepared by in situ carbon filling of one of the barrels by the pyrolytic decompositIon of butane, followed by electrodepositIon of a thin layer of hydrous iridium oxide. The other barrel was filled with an electrolyte solutIon and Ag/AgCl electrode as part of a Conductance cell for SICM. The fabricated probes, with pH and SICM sensing elements typically on the 100 nm scale, were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and various electrochemical measurements. They showed a linear super-Nernstian pH response over a range of pH (pH 2–10). The capability of the pH-SIC...

  • scanning electrochemical cell microscopy theory and experiment for quantitative high resolutIon spatially resolved voltammetry and simultaneous Ion Conductance measurements
    Analytical Chemistry, 2012
    Co-Authors: Michael E. Snowden, Neil Ebejer, Aleix G. Güell, Michael A. Oconnell, Kim Mckelvey, Alexander W. Colburn, Patrick R. Unwin
    Abstract:

    Scanning electrochemical cell microscopy (SECCM) is a high resolutIon electrochemical scanning probe technique that employs a dual-barrel theta pipet probe containing electrolyte solutIon and quasi-reference counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochemical cell. The substrate can be an electrical conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both Ion-Conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillatIon of the probe with respect to the substrate is employed, so that an alternating Conductance current (ac) develops, due to the change in the dimensIons of the electrolyte contact (and hence ...

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