Lateral Resolution and Image Formation in Scanning Ion Conductance Microscopy

Measuring the Shape, Stiffness, and Interface Tension of Droplets with the Scanning Ion Conductance Microscope

Imaging and probing liquid-liquid interfaces at the micro- and nanoscale are of high relevance, for example, in materials science, surface chemistry, and microfluidics. However, existing imaging techniques are limited in resolution, average over large sample areas, or interact with the sample. Here, we present a method to quantify the shape, stiffness, and interface tension of liquid droplets with the scanning ion conductance microscope (SICM), providing submicrometer resolution and the ability to perform noncontact mechanical measurements. We show that we can accurately image the three-dimensional shape of micrometer-sized liquid droplets made of, for example, decane, hexane, or different oils. We then introduce numerical models to quantitatively obtain their stiffness and interface tension from SICM data. We verified our method by measuring the interface tension of decane droplets changing under the influence of surfactants at different concentrations. Finally, we use SICM to resolve the dissolution dynamics of decane droplets, showing that droplet shape exhibits different dissolution modes and stiffness continuously increases while the interface tension remains constant. We thereby demonstrate that SICM is a useful method to investigate liquid-liquid interfaces on the microscale with applications in materials or life sciences.

Membrane fluctuations of human red blood cells investigated by the current signal noise in scanning ion conductance microscopy

Human red blood cells show submicron membrane fluctuations (CMFs) that have been mainly studied with optical microscopies. Although the functional role of this phenomenon is still uncertain, the amplitude of membrane fluctuations is considered as an indicator of mechanical resilience to the stress encountered in the capillary beds. We investigate here the membrane fluctuations in red blood cells using the scanning ion conductance microscopy (SICM), a scanning probe technique that avoids the probe-sample contact. The ion current noise was recorded at a fixed distance from the cell and converted in terms of membrane fluctuation amplitude using as a converting factor the slope of the current-distance curve. We found that CMF amplitude was irreversibly reduced by membrane cross-link. Both whole cell and local increase of membrane tension induced a reduction of CMF amplitude. As for the biochemical regulation of membrane dynamics, we observed that the activation of the noradrenergic transduction pathway, via β-receptors, increased the CMF amplitude. We conclude that the CMFs recorded by SICM and those optically recorded on red blood cells share the main features. In addition SICM provides high spatial and temporal resolution as well as the possibility to apply through the glass pipette acting as probe chemical or physical stimuli to the membrane area where the CMFs are recorded.

The target region focused imaging method for scanning ion conductance microscopy

Scanning ion conductance microscopy (SICM) has developed rapidly and has wide applications in biomedicine, single-cell science and other fields. SICM scanning speed is limited by the conventional raster-type scanning method, which spends most of time on imaging the substrate and does not focus enough on the target area. In order to solve this problem, a target region focused (TRF) method is proposed, which can effectively avoid the scanning of unnecessary substrate areas and enables SICM to image the target area only to achieve high-speed and effective local scanning. TRF method and conventional hopping mode scanning method are compared in the experiments using breast cancer cells and rat basophilic leukemia cells as experimental materials. It was demonstrated that our method can reduce the scanning time for a single sample image significantly without losing scanning information or compromising the quality of imaging. The TRF method developed in this paper can provide an efficient and fast scanning strategy for improving the imaging performance of SICM systems, which can be applied to the dynamic features of cell samples in the fields of biology and pharmacology analysis.

Visualization of the membrane surface and cytoskeleton of oligodendrocyte progenitor cell growth cones using a combination of scanning ion conductance and four times expansion microscopy

Growth cones of oligodendrocyte progenitor cells (OPCs) are challenging to investigate with conventional light microscopy due to their small size. Especially substructures such as filopodia, lamellipodia and their underlying cytoskeleton are difficult to resolve with diffraction limited microscopy. Light microscopy techniques, which surpass the diffraction limit such as stimulated emission depletion microscopy, often require expensive setups and specially trained personnel rendering them inaccessible to smaller research groups. Lately, the invention of expansion microscopy (ExM) has enabled super-resolution imaging with any light microscope without the need for additional equipment. Apart from the necessary resolution, investigating OPC growth cones comes with another challenge: Imaging the topography of membranes, especially label- and contact-free, is only possible with very few microscopy techniques one of them being scanning ion conductance microscopy (SICM). We here present a new imaging workflow combining SICM and ExM, which enables the visualization of OPC growth cone nanostructures. We correlated SICM recordings and ExM images of OPC growth cones captured with a conventional widefield microscope. This enabled the visualization of the growth cones' membrane topography as well as their underlying actin and tubulin cytoskeleton.

Scanning ion conductance microscopy revealed cisplatin-induced morphological changes related to apoptosis in single adenocarcinoma cells

The studies of drug-induced apoptosis play a vital role in the identification of potential drugs that could treat diseases such as cancer. Alterations in the native morphology of cancer cells following treatment with anticancer drugs serve as one of the indicators that reveal drug efficacy. Various techniques such as optical microscopy, electron microscopy (EM), and atomic force microscopy (AFM) have been used to map the three dimensional (3D) morphological changes in cells induced with drugs. However, caution should be exercised when interpreting morphological data from techniques that might alter the native morphology of cells, caused by phototoxicity, electron beam invasiveness, intrusive sample preparation, and cell membrane deformation. Herein, we have used scanning ion conductance microscopy (SICM) to study the 3D morphology and roughness of A549 adenocarcinoma cells under physiological conditions before and after cisplatin induced apoptosis, where we observed an increase in height, overall shrinkage of the cells, and irregular features form on the cell membrane. Tracking the morphology of the same single A549 cells exposed to cisplatin unveiled heterogeneity in response to the drug, formation of membrane blebs, and an increase in membrane roughness. We have also demonstrated the use of SICM for studying the effect of cisplatin on the dynamic changes in the volume of A549 cells over days. SICM is demonstrated as a technique for studying the effect of drug induced apoptosis in the same cells over time, and for multiple different single cells.

Opto-SICM framework combines optogenetics with scanning ion conductance microscopy for probing cell-to-cell contacts

We present a novel framework, Opto-SICM, for studies of cellular interactions in live cells with high spatiotemporal resolution. The approach combines scanning ion conductance microscopy, SICM, and cell-type-specific optogenetic interrogation. Light-excitable cardiac fibroblasts (FB) and myofibroblasts (myoFB) were plated together with non-modified cardiomyocytes (CM) and then paced with periodic illumination. Opto-SICM reveals the extent of FB/myoFB-CM cell-cell contacts and the dynamic changes over time not visible by optical microscopy. FB-CM pairs have lower gap junctional expression of connexin-43 and higher contact dynamism compared to myoFB-CM pairs. The responsiveness of CM to pacing via FB/myoFB depends on the dynamics of the contact but not on the area. The non-responding pairs have higher net cell-cell movement at the contact. These findings are relevant to cardiac disease states, where adverse remodeling leads to abnormal electrical excitation of CM. The Opto-SICM framework can be deployed to offer new insights on cellular and subcellular interactions in various cell types, in real-time.

Scanning ion conductance microscope with a capacitance-compensated current source amplifier

A high-speed imaging method for a scanning ion conductance microscope (SICM) based on a current source amplifier that compensates for unavoidable capacitance is proposed. The capacitance is generated on a side wall of a nanopipette in the principle of the SICM. The electrical response time is deteriorated due to the capacitance, and the probe overshoots the setpoint of the detection of the sample surface. A capacitance compensation circuit was installed in a feedback circuit of the current source amplifier. The proposed capacitance compensation method is useful because it can shorten the imaging time by only installing the compensation circuit in the ion current detection circuit of an existing SICM. The maximum approaching speeds with and without capacitance compensation were found to be 1050 and 450 µm/s, respectively. The approaching speed with capacitance compensation was 2.3 times faster than that without capacitance compensation. A topographic image of the test sample was successfully obtained at an approaching speed of 1050 µm/s. The images of microvillus dynamics of COS-7 cells were obtained at ∼23.4 s/frame as an application of the developed technology.

The Modification and Applications of Nanopipettes in Electrochemical Analysis

Nanopipette, which is fabricated by glasses and possesses a nanoscale pore in the tip, has been proven to be immensely useful in electrochemical analysis. Numerous nanopipette-based sensors have emerged with improved sensitivity, selectivity, ease of use, and miniaturization. In this minireview, we provide an overview of the recent developments of nanopipette-based electrochemical sensors based on different types of nanopipettes, including single-nanopipettes, self-referenced nanopipettes, dual-nanopipettes, and double-barrel nanopipettes. Several important modification materials for nanopipette functionalization are highlighted, such as conductive materials, macromolecular materials, and functional molecules. These materials can improve the sensing performance and targeting specificities of nanopipettes. We also discuss examples of related applications and the future development of nanopipette-based strategies.

Response of Osteoblasts to Electric Field Line Patterns Emerging from Molecule Stripe Landscapes

Molecular surface gradients can constitute electric field landscapes and serve to control local cell adhesion and migration. Cellular responses to electric field landscapes may allow the discovery of routes to improve osseointegration of implants. Flat molecule aggregate landscapes of amine- or carboxyl-teminated dendrimers, amine-containing protein and polyelectrolytes were prepared on glass to provide lateral electric field gradients through their differing zeta potentials compared to the glass substrate. The local as well as the mesoscopic morphological responses of adhered osteoblasts (MG-63) with respect to the stripes were studied by means of Scanning Ion Conductance Microscopy (SICM) and Fluorescence Microscopy, in situ. A distinct spindle shape oriented parallel to the surface pattern as well as a preferential adhesion of the cells on the glass site have been observed at a stripe and spacing width of 20 μm. Excessive ruffling is observed at the spindle poles, where the cells extend. To explain this effect of material preference and electro-deformation, we put forward a retraction mechanism, a localized form of double-sided cathodic taxis.

Time-Resolved Scanning Ion Conductance Microscopy for Three-Dimensional Tracking of Nanoscale Cell Surface Dynamics

Nanocharacterization plays a vital role in understanding the complex nanoscale organization of cells and organelles. Understanding cellular function requires high-resolution information about how the cellular structures evolve over time. A number of techniques exist to resolve static nanoscale structure of cells in great detail (super-resolution optical microscopy, EM, AFM). However, time-resolved imaging techniques tend to either have a lower resolution, are limited to small areas, or cause damage to the cells, thereby preventing long-term time-lapse studies. Scanning probe microscopy methods such as atomic force microscopy (AFM) combine high-resolution imaging with the ability to image living cells in physiological conditions. The mechanical contact between the tip and the sample, however, deforms the cell surface, disturbs the native state, and prohibits long-term time-lapse imaging. Here, we develop a scanning ion conductance microscope (SICM) for high-speed and long-term nanoscale imaging of eukaryotic cells. By utilizing advances in nanopositioning, nanopore fabrication, microelectronics, and controls engineering, we developed a microscopy method that can resolve spatiotemporally diverse three-dimensional (3D) processes on the cell membrane at sub-5-nm axial resolution. We tracked dynamic changes in live cell morphology with nanometer details and temporal ranges of subsecond to days, imaging diverse processes ranging from endocytosis, micropinocytosis, and mitosis to bacterial infection and cell differentiation in cancer cells. This technique enables a detailed look at membrane events and may offer insights into cell-cell interactions for infection, immunology, and cancer research.

Scanning Ion Conductance Microscopy

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.

Correlative 3D microscopy of single cells using super-resolution and scanning ion-conductance microscopy

High-resolution live-cell imaging is necessary to study complex biological phenomena. Modern fluorescence microscopy methods are increasingly combined with complementary, label-free techniques to put the fluorescence information into the cellular context. The most common high-resolution imaging approaches used in combination with fluorescence imaging are electron microscopy and atomic-force microscopy (AFM), originally developed for solid-state material characterization. AFM routinely resolves atomic steps, however on soft biological samples, the forces between the tip and the sample deform the fragile membrane, thereby distorting the otherwise high axial resolution of the technique. Here we present scanning ion-conductance microscopy (SICM) as an alternative approach for topographical imaging of soft biological samples, preserving high axial resolution on cells. SICM is complemented with live-cell compatible super-resolution optical fluctuation imaging (SOFI). To demonstrate the capabilities of our method we show correlative 3D cellular maps with SOFI implementation in both 2D and 3D with self-blinking dyes for two-color high-order SOFI imaging. Finally, we employ correlative SICM/SOFI microscopy for visualizing actin dynamics in live COS-7 cells with subdiffraction-resolution.

Geometrical Characterization of Glass Nanopipettes with Sub-10 nm Pore Diameter by Transmission Electron Microscopy

Glass nanopipettes are widely used for various applications in nanosciences. In most of the applications, it is important to characterize their geometrical parameters, such as the aperture size and the inner cone angle at the tip region. For nanopipettes with sub-10 nm aperture and thin wall thickness, transmission electron microscopy (TEM) must be most instrumental in their precise geometrical measurement. However, this measurement has remained a challenge because heat generated by electron beam irradiation would largely deform sub-10 nm nanopipettes. Here, we provide methods for preparing TEM specimens that do not cause deformation of such tiny nanopipettes.

A High Accuracy Ion Conductance Imaging Method Based on the Approach Curve Spectrum

Scanning ion conductance microscopy (SICM), as an emerging non-contact in situ topography measurement tool with nano resolution, has been increasingly used in recent years in biomedicine, electrochemistry and materials science. In the conventional measurement method of SICM, the sample topography is constructed according to the position of the probe at the feedback threshold of the ion current. Nevertheless, for different structures, a constant threshold cannot maintain a constant probe-sample distance. This phenomenon makes the measurement topography inconsistent with the real sample surface. In order to solve this problem and improve the measurement accuracy of SICM, a new ion conductance imaging method based on the approach curve spectrum is proposed in this work. In the new method, the local feature around the measurement point is firstly evaluated according to the change rate of ion current. Secondly, based on the local feature, the corresponding approach curve is searched from the prior approach curve spectrum to accurately evaluate the distance between the probe and the sample. Finally, the sample topography is constructed by the probe position subtracting the probe-sample distance. In this paper, we verify the feasibility of the new imaging method by combining finite element theory and experiments. To examine the measurement accuracy, the standard strip silicon and cylindrical polydimethylsiloxane (PDMS) samples are tested, and the improved imaging method can obtain the topography closer to the real samples and reduce the volumetric measurement error by 5.4%. The implementation of the new imaging method will further promote SICM application in related research fields.

Quantifying single-platelet biomechanics: An outsider's guide to biophysical methods and recent advances

Platelets are the key cellular components of blood primarily contributing to formation of stable hemostatic plugs at the site of vascular injury, thus preventing excessive blood loss. On the other hand, excessive platelet activation can contribute to thrombosis. Platelets respond to many stimuli that can be of biochemical, cellular, or physical origin. This drives platelet activation kinetics and plays a vital role in physiological and pathological situations. Currently used bulk assays are inadequate for comprehensive biomechanical assessment of single platelets. Individual platelets interact and respond differentially while modulating their biomechanical behavior depending on dynamic changes that occur in surrounding microenvironments. Quantitative description of such a phenomenon at single-platelet regime and up to nanometer resolution requires methodological approaches that can manipulate individual platelets at submicron scales. This review focusses on principles, specific examples, and limitations of several relevant biophysical methods applied to single-platelet analysis such as micropipette aspiration, atomic force microscopy, scanning ion conductance microscopy and traction force microscopy. Additionally, we are introducing a promising single-cell approach, real-time deformability cytometry, as an emerging biophysical method for high-throughput biomechanical characterization of single platelets. This review serves as an introductory guide for clinician scientists and beginners interested in exploring one or more of the above-mentioned biophysical methods to address outstanding questions in single-platelet biomechanics.

Development of high-speed ion conductance microscopy

Scanning ion conductance microscopy (SICM) can image the surface topography of specimens in ionic solutions without mechanical probe-sample contact. This unique capability is advantageous for imaging fragile biological samples but its highest possible imaging rate is far lower than the level desired in biological studies. Here, we present the development of high-speed SICM. The fast imaging capability is attained by a fast Z-scanner with active vibration control and pipette probes with enhanced ion conductance. By the former, the delay of probe Z-positioning is minimized to sub-10 µs, while its maximum stroke is secured at 6 μm. The enhanced ion conductance lowers a noise floor in ion current detection, increasing the detection bandwidth up to 100 kHz. Thus, temporal resolution 100-fold higher than that of conventional systems is achieved, together with spatial resolution around 20 nm.

Thermally Driven Approach To Fill Sub-10-nm Pipettes with Batch Production

Typically, utilization of small nanopipettes results in either high sensitivity or spatial resolution in modern nanoscience and nanotechnology. However, filling a nanopipette with a sub-10-nm pore diameter remains a significant challenge. Here, we introduce a thermally driven approach to filling sub-10-nm pipettes with batch production, regardless of their shape. A temperature gradient is applied to transport water vapor from the backside of nanopipettes to the tip region until bubbles are completely removed from this region. The electrical contact and pore size for filling nanopipettes are confirmed by current-voltage and transmission electron microscopy (TEM) measurements, respectively. In addition, we quantitatively compare the pore size between the TEM characterization and estimation on the basis of pore radius and conductance. The validity of this method provides a foundation for highly sensitive detection of single molecules and high spatial resolution imaging of nanostructures.

Ultrafast Imaging of Cardiomyocyte Contractions by Combining Scanning Ion Conductance Microscopy with a Microelectrode Array

Beating cardiomyocytes undergo fast morphodynamics during the contraction-relaxation cycle. However, imaging these morphodynamics with a high spatial and temporal resolution is difficult, owing to a lack of suitable techniques. Here, we combine scanning ion conductance microscopy (SICM) with a microelectrode array (MEA) to image the three-dimensional (3D) topography of cardiomyocytes during a contraction-relaxation cycle with 1 μm spatial and 1 ms time resolution. We record the vertical motion of cardiomyocytes at many locations across a cell by SICM and synchronize these data using the simultaneously recorded action potential by the MEA as a time reference. This allows us to reconstruct the time-resolved 3D morphology of cardiomyocytes during a full contraction-relaxation cycle with a raw data rate of 200 μs/frame and to generate spatially resolved images of contractile parameters (maximum displacement, time delay, asymmetry factor). We use the MEA-SICM setup to visualize the effect of blebbistatin, a myosin II inhibitor, on the morphodynamics of contractions. Further, we find an upper limit of 0.02% for cell volume changes during an action potential. The results show that MEA-SICM provides an ultrafast imaging platform for investigating the functional interplay of cardiomyocyte electrophysiology and mechanics.

High-speed scanning ion conductance microscopy for sub-second topography imaging of live cells

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.

A fast scanning ion conductance microscopy imaging method using compressive sensing and low-discrepancy sequences

A scanning ion conductance microscope (SICM) is a multifunctional, high-resolution imaging technique whose non-contact nature makes it very suitable for imaging of biological samples such as living cells in a physiological environment. However, a drawback of hopping/backstep mode of SICM is its relatively slow imaging speed, which seriously restricts the study on the dynamic process of biological samples. This paper presents a new undersampled scanning method based on Compressed Sensing (CS-based scanning mode) theory to solve extended acquisition time issues in the hopping/backstep mode. Compressive sensing can break through the limit of the Nyquist sampling theorem and sample the original sparse/compressible signal at a rate lower than the Nyquist frequency. In the CS-based scanning mode, three sampling patterns, including the random sampling pattern and two kinds of sampling patterns produced by low-discrepancy sequences, were employed as the measurement locations to obtain the undersampled data with different undersampling ratios. Also TVAL3 (Total Variation Augmented Lagrangian ALternating-direction ALgorithm) was then utilized as a reconstruction algorithm to reconstruct the undersampled data. Compared with the nonuniform sampling points of random patterns at a low undersampling ratio, low-discrepancy sequences can produce a more uniform distribution point. Three types of samples with different complexity of topography were scanned by SICM using the conventional hopping/backstep mode and CS-based undersampled scanning mode. The comparisons of the imaging speed and quality with two scanning modes illustrate that the CS-based scanning mode can effectively speed up SICM imaging speed while not sacrificing the image quality. Also low-discrepancy sampling patterns can achieve a better reconstruction performance than that of the random sampling pattern under the same undersampling ratio.

Correlative Stimulated Emission Depletion and Scanning Ion Conductance Microscopy

Correlation microscopy combining fluorescence and scanning probe or electron microscopy is limited to fixed samples due to the sample preparation and nonphysiological imaging conditions required by most probe or electron microscopy techniques. Among the few scanning probe techniques that allow imaging of living cells under physiological conditions, scanning ion conductance microscopy (SICM) has been shown to be the technique that minimizes the impact on the investigated sample. However, combinations of SICM and fluorescence microscopy suffered from the mismatch in resolution due to the limited resolution of conventional light microscopy. In the last years, the diffraction limit of light microscopy has been circumvented by various techniques, one of which is stimulated emission depletion (STED) microscopy. Here, we aimed at demonstrating the combination of STED and SICM. We show that both methods allow recording a living cellular specimen and provide a SICM and STED image of the same sample, which allowed us to correlate the membrane surface topography and the distribution of the cytoskeletal protein actin. Our proof-of-concept study exemplifies the benefit of correlating SICM with a subdiffraction fluorescence method and might form the basis for the development of a combined instrument that would allow the simultaneous recording of subdiffraction fluorescence and topography information.

Smart Scanning Ion-Conductance Microscopy Imaging Technique Using Horizontal Fast Scanning Method

To solve extended acquisition time issues inherent in the conventional hopping-scanning mode of scanning ion-conductance microscopy (SICM), a new transverse-fast scanning mode (TFSM) is proposed. Because the transverse motion in SICM is not the detection direction and therefore presents no collision problem, it has the ability to move at high speed. In TSFM, the SICM probe gradually descends in the vertical/detection direction and rapidly scans in the transverse/nondetection direction. Further, the highest point that decides the hopping height of each scanning line can be quickly obtained. In conventional hopping mode, however, the hopping height is artificially set without a priori knowledge and is typically very large. Consequently, TFSM greatly improves the scanning speed of the SICM imaging system by effectively reducing the hopping height of each pixel. This study verifies the feasibility of this novel scanning method via theoretical analysis and experimental study, and compares the speed and quality of the scanning images obtained in the TFSM with that of the conventional hopping mode. The experimental results indicate that the TFSM method has a faster scanning speed than other SICM scanning methods while maintaining the quality of the images. Therefore, TFSM provides the possibility to quickly obtain high-resolution three-dimensional topographical images of extremely complex samples.

Macro-SICM: A Scanning Ion Conductance Microscope for Large-Range Imaging

The scanning ion conductance microscope (SICM) is a versatile, high-resolution imaging technique that uses an electrolyte-filled nanopipet as a probe. Its noncontact imaging principle makes the SICM uniquely suited for the investigation of soft and delicate surface structures in a liquid environment. The SICM has found an ever-increasing number of applications in chemistry, physics, and biology. However, a drawback of conventional SICMs is their relatively small scan range (typically 100 μm × 100 μm in the lateral and 10 μm in the vertical direction). We have developed a Macro-SICM with an exceedingly large scan range of 25 mm × 25 mm in the lateral and 0.25 mm in the vertical direction. We demonstrate the high versatility of the Macro-SICM by imaging at different length scales: from centimeters (fingerprint, coin) to millimeters (bovine tongue tissue, insect wing) to micrometers (cellular extensions). We applied the Macro-SICM to the study of collective cell migration in epithelial wound healing.

A low-cost, large field-of-view scanning ion conductance microscope for studying nanoparticle-cell membrane interactions

Nanoparticles have the potential to become versatile tools in the medical and life sciences. One potential application is delivering drugs or other compounds to the cell cytoplasm, which requires the nanoparticles to bind to or cross the cell membrane. However, there are only a few tools available which allow studying the interaction of nanoparticles and the cell membrane of living cells in a physiological environment. Currently, the tool which least biases living cells is Scanning Ion Conductance Microscopy (SICM). Specialized SICMs allow imaging at high resolution, however, they are cost intensive, particularly when providing a large field-of-view. In contrast, less cost intensive SICMs which provide a large field-of-view do not allow imaging at high resolutions. We have developed a SICM setup consisting of a compact three-axis piezo system and an additional fast shear-force piezo actor. This combination allows imaging fields-of-view of up to 80 μm × 80 μm, recording sections of living cells with a temporal resolution in the range of minutes as well as imaging with a spatial resolution of below 70 nm. Using our SICM we found that the cell membrane of HeLa cells treated with carboxylated latex nanoparticles was significantly more convoluted compared to control cells. The SICM setup we introduce here combines high resolution imaging with a large field-of-view at low costs. Our setup only requires a mounting adapter to extend existing inverted light microscopes, thus it could be a valuable and cost effective tool for researchers in all fields of the medical and life sciences performing investigations at the nanometer scale.

Thrombin-induced cytoskeleton dynamics in spread human platelets observed with fast scanning ion conductance microscopy

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.

Double micropipettes configuration method of scanning ion conductance microscopy

In this paper, a new double micropipettes configuration mode of scanning ion conductance microscopy (SICM) is presented to better overcome ionic current drift and further improve the performance of SICM, which is based on a balance bridge circuit. The article verifies the feasibility of this new configuration mode from theoretical and experimental analyses, respectively, and compares the quality of scanning images in the conventional single micropipette configuration mode and the new double micropipettes configuration mode. The experimental results show that the double micropipettes configuration mode of SICM has better effect on restraining ionic current drift and better performance of imaging. Therefore, this article not only proposes a new direction of overcoming the ionic current drift but also develops a new method of SICM stable imaging.

Angular Approach Scanning Ion Conductance Microscopy

Scanning ion conductance microscopy (SICM) is a super-resolution live imaging technique that uses a glass nanopipette as an imaging probe to produce three-dimensional (3D) images of cell surface. SICM can be used to analyze cell morphology at nanoscale, follow membrane dynamics, precisely position an imaging nanopipette close to a structure of interest, and use it to obtain ion channel recordings or locally apply stimuli or drugs. Practical implementations of these SICM advantages, however, are often complicated due to the limitations of currently available SICM systems that inherited their design from other scanning probe microscopes in which the scan assembly is placed right above the specimen. Such arrangement makes the setting of optimal illumination necessary for phase contrast or the use of high magnification upright optics difficult. Here, we describe the designs that allow mounting SICM scan head on a standard patch-clamp micromanipulator and imaging the sample at an adjustable approach angle. This angle could be as shallow as the approach angle of a patch-clamp pipette between a water immersion objective and the specimen. Using this angular approach SICM, we obtained topographical images of cells grown on nontransparent nanoneedle arrays, of islets of Langerhans, and of hippocampal neurons under upright optical microscope. We also imaged previously inaccessible areas of cells such as the side surfaces of the hair cell stereocilia and the intercalated disks of isolated cardiac myocytes, and performed targeted patch-clamp recordings from the latter. Thus, our new, to our knowledge, angular approach SICM allows imaging of living cells on nontransparent substrates and a seamless integration with most patch-clamp setups on either inverted or upright microscopes, which would facilitate research in cell biophysics and physiology.

Comparative morphology analysis of live blood platelets using scanning ion conductance and robotic dark-field microscopy

Many 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 that SICM and RDM are both valuable tools for the ex vivo investigation of the morphology of live platelets, which might contribute to new insights into the physiological and pathophysiological role of platelet spreading.

Simultaneous Scanning Ion Conductance Microscopy and Atomic Force Microscopy with Microchanneled Cantilevers

We combined scanning ion conductance microscopy (SICM) and atomic force microscopy (AFM) into a single tool using AFM cantilevers with an embedded microchannel flowing into the nanosized aperture at the apex of the hollow pyramid. An electrode was positioned in the AFM fluidic circuit connected to a second electrode in the bath. We could thus simultaneously measure the ionic current and the cantilever bending (in optical beam deflection mode). First, we quantitatively compared the SICM and AFM contact points on the approach curves. Second, we estimated where the probe in SICM mode touches the sample during scanning on a calibration grid and applied the finding to image a network of neurites on a Petri dish. Finally, we assessed the feasibility of a double controller using both the ionic current and the deflection as input signals of the piezofeedback. The experimental data were rationalized in the framework of finite elements simulations.