Chemically imaging living cells by scanning electrochemical microscopy

Exploring the Living Cell: Applications and Advances of Scanning Electrochemical Microscopy

A living cell is a complex network of molecular, biochemical and physiological processes. Cellular activities, such as ion transport, metabolic processes, and cell-cell interactions can be determined electrochemically by detecting the electrons or ions exchanged in these processes. Electrochemical methods often are noninvasive, and they can enable the real-time monitoring of cellular processes. Scanning electrochemical microscopy (SECM) is an advanced scanning probe electroanalysis technique that can map the surface topography and local reactivity of a substrate with high precision at the micro- or nanoscale. By measuring electrochemical signals, such as redox reactions, ion fluxes, and pH changes, SECM can provide valuable insights into cellular activity. As a result of its compatibility with liquid medium measurements and its nondestructive nature, SECM has gained popularity in living cell research. This review aims to furnish an overview of SECM, elucidating its principles, applications, and its potential to contribute significantly to advancements in cell biology, electroporation, and biosensors. As a multidisciplinary tool, SECM is distinguished by its ability to unravel the intricacies of living cells and offers promising avenues for breakthroughs in our understanding of cellular complexity.

A review of innovative electrochemical strategies for bioactive molecule detection and cell imaging: Current advances and challenges

Cellular heterogeneity poses a major challenge for tumor theranostics, requiring high-resolution intercellular bioanalysis strategies. Over the past decades, the advantages of electrochemical analysis, such as high sensitivity, good spatio-temporal resolution, and ease of use, have made it the preferred method to uncover cellular differences. To inspire more creative research, herein, we highlight seminal works in electrochemical techniques for biomolecule analysis and bioimaging. Specifically, micro/nano-electrode-based electrochemical techniques enable real-time quantitative analysis of electroactive substances relevant to life processes in the micro-nanostructure of cells and tissues. Nanopore-based technique plays a vital role in biosensing by utilizing nanoscale pores to achieve high-precision detection and analysis of biomolecules with exceptional sensitivity and single-molecule resolution. Electrochemiluminescence (ECL) technology is utilized for real-time monitoring of the behavior and features of individual cancer cells, enabling observation of their dynamic processes due to its capability of providing high-resolution and highly sensitive bioimaging of cells. Particularly, scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) which are widely used in real-time observation of cell surface biological processes and three-dimensional imaging of micro-nano structures, such as metabolic activity, ion channel activity, and cell morphology are introduced in this review. Furthermore, the expansion of the scope of cellular electrochemistry research by innovative functionalized electrodes and electrochemical imaging models and strategies to address future challenges and potential applications is also discussed in this review.

Can Single Cell Respiration be Measured by Scanning Electrochemical Microscopy (SECM)?

Ultramicroelectrode (UME), or, equivalently, microelectrode, probes are increasingly used for single-cell measurements of cellular properties and processes, including physiological activity, such as metabolic fluxes and respiration rates. Major challenges for the sensitivity of such measurements include: (i) the relative magnitude of cellular and UME fluxes (manifested in the current); and (ii) issues around the stability of the UME response over time. To explore the extent to which these factors impact the precision of electrochemical cellular measurements, we undertake a systematic analysis of measurement conditions and experimental parameters for determining single cell respiration rates via the oxygen consumption rate (OCR) in single HeLa cells. Using scanning electrochemical microscopy (SECM), with a platinum UME as the probe, we employ a self-referencing measurement protocol, rarely employed in SECM, whereby the UME is repeatedly approached from bulk solution to a cell, and a short pulse to oxygen reduction reaction (ORR) potential is performed near the cell and in bulk solution. This approach enables the periodic tracking of the bulk UME response to which the near-cell response is repeatedly compared (referenced) and also ensures that the ORR near the cell is performed only briefly, minimizing the effect of the electrochemical process on the cell. SECM experiments are combined with a finite element method (FEM) modeling framework to simulate oxygen diffusion and the UME response. Taking a realistic range of single cell OCR to be 1 × 10-18 to 1 × 10-16 mol s-1, results from the combination of FEM simulations and self-referencing SECM measurements show that these OCR values are at, or below, the present detection sensitivity of the technique. We provide a set of model-based suggestions for improving these measurements in the future but highlight that extraordinary improvements in the stability and precision of SECM measurements will be required if single cell OCR measurements are to be realized.

Deconvoluting Kinetic Rate Constants of Catalytic Substrates from Scanning Electrochemical Approach Curves with Artificial Neural Networks

Extracting information from experimental measurements in the chemical sciences typically requires curve fitting, deconvolution, and/or solving the governing partial differential equations via numerical (e.g., finite element analysis) or analytical methods. However, using numerical or analytical methods for high-throughput data analysis typically requires significant postprocessing efforts. Here, we show that deep learning artificial neural networks can be a very effective tool for extracting information from experimental data. As an example, reactivity and topography information from scanning electrochemical microscopy (SECM) approach curves are highly convoluted. This study utilized multilayer perceptrons and convolutional neural networks trained on simulated SECM data to extract kinetic rate constants of catalytic substrates. Our key findings were that multilayer perceptron models performed very well when the experimental data were close to the ideal conditions with which the model was trained. However, convolutional neural networks, which analyze images as opposed to direct data, were able to accurately predict the kinetic rate constant of Fe-doped nickel (oxy)hydroxide catalyst at different applied potentials even though the experimental approach curves were not ideal. Due to the speed at which machine learning models can analyze data, we believe this study shows that artificial neural networks could become powerful tools in high-throughput data analysis.

An anticancer Ti(IV) complex increases mitochondrial reactive oxygen species levels in relation with hypoxia and endoplasmic-reticulum stress: A distinct non DNA-related mechanism

PhenolaTi is a promising Ti(IV) anticancer complex, with high stability and cytotoxicity, without notable toxic side-effects. Its cellular mechanism was proposed to relate to ER stress. Herein, we investigated the downstream effects of this mode of action in two cancer cell lines: ovarian carcinoma A2780 and cervical adenocarcinoma HeLa. First, although Ti(IV) is a non-redox metal, the formation of mitochondrial reactive oxygen species (ROS) was detected with live-cell imaging. Then, we inspected the effect of the mitochondrial ROS on cytotoxicity, using two methods: (a) addition of compounds that either elevate or reduce the mitochondrial glutathione concentration, thus affecting the oxidative state of the cells; and (b) scavenging mitochondrial ROS. Unlike the results observed for cisplatin, neither method influenced the cytotoxicity of phenolaTi, implying that ROS formation was a mere side effect of its activity. Additionally, live cell imaging displayed the hypoxia induced by phenolaTi, which can be associated with ROS formation. Overall, the results support the notion that ER-stress is the main cellular mechanism of phenolaTi, leading to hypoxia and mitochondrial ROS. The distinct mechanism of phenolaTi, which is different from that of cisplatin, combined with its stability and favorable anticancer properties, altogether make it a strong chemotherapeutic drug candidate.

In Situ and Quantitatively Monitoring the Dynamic Process of Ferroptosis in Single Cancer Cells by Scanning Electrochemical Microscopy

Ferroptosis, as a promising therapeutic strategy for cancers, has aroused great interest. Quantifying the quick dynamic changes in key parameters during the early course of ferroptosis can provide insights for understanding the underlying mechanisms of ferroptosis and help the development of therapies targeting ferroptosis. However, in situ and quantitatively monitoring the quick responses of living cancer cells to ferroptosis at the single-cell level remains technically challenging. In this work, we selected HuH7 cells (hepatocellular carcinoma (HCC) cells) as a cell model and Erastin as a typical ferroptosis inducer. We utilized scanning electrochemical microscopy (SECM) to quantitatively and in situ monitor the early course of ferroptosis in HuH7 cells by characterizing the three key parameters of cell ferroptosis (i.e., cell membrane permeability, respiratory activity, and the redox state). The SECM results show that the membrane permeability of ferroptotic HuH7 cells continuously increased from 0 to 8.1 × 10-5 m s-1, the cellular oxygen consumption was continuously reduced by half, and H2O2 released from the cells exhibited periodic bursts during the early course of ferroptosis, indicating the gradually destroyed cell membrane structure and intensified oxidative stress. Our work realizes, for the first time, the in situ and quantitative monitoring of the cell membrane permeability, respiratory activity, and H2O2 level of the early ferroptosis process of a single living cancer cell with SECM, which can contribute to the understanding of the physiological process and underlying mechanisms of ferroptosis.

Enzymatic and Microbial Electrochemistry: Approaches and Methods

The coupling of enzymes and/or intact bacteria with electrodes has been vastly investigated due to the wide range of existing applications. These span from biomedical and biosensing to energy production purposes and bioelectrosynthesis, whether for theoretical research or pure applied industrial processes. Both enzymes and bacteria offer a potential biotechnological alternative to noble/rare metal-dependent catalytic processes. However, when developing these biohybrid electrochemical systems, it is of the utmost importance to investigate how the approaches utilized to couple biocatalysts and electrodes influence the resulting bioelectrocatalytic response. Accordingly, this tutorial review starts by recalling some basic principles and applications of bioelectrochemistry, presenting the electrode and/or biocatalyst modifications that facilitate the interaction between the biotic and abiotic components of bioelectrochemical systems. Focus is then directed toward the methods used to evaluate the effectiveness of enzyme/bacteria-electrode interaction and the insights that they provide. The basic concepts of electrochemical methods widely employed in enzymatic and microbial electrochemistry, such as amperometry and voltammetry, are initially presented to later focus on various complementary methods such as spectroelectrochemistry, fluorescence spectroscopy and microscopy, and surface analytical/characterization techniques such as quartz crystal microbalance and atomic force microscopy. The tutorial review is thus aimed at students and graduate students approaching the field of enzymatic and microbial electrochemistry, while also providing a critical and up-to-date reference for senior researchers working in the field.

Electrochemical sensors for oral biofilm-biomaterials interface characterization: A review

Important processes related to the interaction of the oral microbiome with the tooth surface happen directly at the interface. For example, the chemical microenvironment that exists at the interface of microbial biofilms and the native tooth structure is directly involved in caries development. Consequentially, a critical understanding of this interface and its chemical microenvironment would provide novel avenues in caries prevention, including secondary caries that often occurs at the interface of the dental biofilm, tooth structure, and dental material. Electrochemical sensors are a unique quantitative tool and have the inherent advantages of miniaturization, stability, and selectivity. That makes the electrochemical sensors ideal tools for studying these critical biofilm microenvironments with high precision. This review highlights the development and applications of several novel electrochemical sensors such as pH, Ca2+ , and hydrogen peroxide sensors as scanning electrochemical microscope probes in addition to flexible pH wire sensors for real-time bacterial biofilm-dental surface and dental materials interface studies.

In situ monitoring of the effect of Cu2+ on the membrane permeability of a single living cell with a dual-electrode tip of a scanning electrochemical microscope

Here, an Au-Cu dual-electrode tip was designed to monitor the effect of Cu²⁺ on the membrane permeability of a single living cell in situ using scanning electrochemical microscopy. The probe approach curves (PACs) were obtained using potassium ferricyanide as a redox mediator. Meanwhile, according to the simulation, theoretical PACs could be acquired. Thus, the cell membrane permeability coefficient (P_m) values were obtained by overlapping the experimental PACs with the theoretical values. Cu²⁺ was directly generated by electrolyzing the Cu electrode of the dual-electrode tip to investigate its effect on the cell membrane permeability in situ. This work has potential value to improve the understanding of the mechanism of acute heavy metal damage on the cell membrane and will also help clarify the role of heavy metal ions in physiological or pathological processes.

Real-time effects of Cd(II) on the cellular membrane permeability

Cell membrane permeability is one of the main indicators of cytotoxicity and related to many critical biological pathways. Here, we determined the Cd²⁺-induced membrane permeability of human MCF-7 cells using ferrocene methanol molecular probes based on scanning electrochemical microscopy (SECM). The cell height and topography were examined with an impermeable Ru(NH₃)₆Cl₃ probe. The membrane permeability exhibited no significant changes when the Cd²⁺ incubation time was less than 2 h and its concentration was less than 40 μM. The permeability increased when the Cd²⁺ concentration was greater than 60 μM, or when the incubation time was longer than 3 h. From the combined 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and cytoskeleton imaging experiments, it was found that the changes occurred because the cells exhibited a defensive mode and their membranes contracted when treated with a low concentration of Cd²⁺ for a short time. However, the cell membranes were irreversibly damaged when the cytoskeleton structures were destroyed, and the cell activities decreased at high concentrations over long periods. Interestingly, through the comparison with an x-scan study, it was found that DPV technology shows a higher performance in the detection of changes in the membrane permeability. Using a combination of cytoskeleton fluorescence imaging and cell-viability tests, the effect of the cadmium metal on the cell membrane permeability can be explored deeper and more comprehensively. This study provides a new idea for exploring the changes in the cell membrane permeability and may be helpful for rapid evaluation of cytotoxicity.

Theoretical and experimental verification of imaging resolution factors in scanning electrochemical microscopy

The imaging resolution of scanning electrochemical microscopy (SECM) depends strongly on the tip electrode size and the tip-substrate distance. Herein, etched glass encapsulation was applied to fabricate a gold disk electrode, and the size of the tip electrode was accurately determined from the steady-state limiting current. Referring to the theoretical research carried out by our predecessors, the formula for the imaging resolution was derived, followed by the imaging of gold spots and cells with the prepared microelectrodes of different sizes and with different tip-substrate distances. A depth scan was performed to generate 2D current maps of the gold spot relative to the position of the microelectrode in the x-z plane. Probe approach curves and horizontal sweeps were obtained from one depth scan image by simply extracting vertical and horizontal cross-sectional lines, and further characterized by comparison with simulated curves through modeling of the experimental system. The experimental results were basically consistent with the theory, revealing that the highest imaging resolution can be obtained with the smallest tip electrode when d/a = 1, and when the size of the tip electrode is fixed the smallest tip-substrate distance can give the highest imaging resolution.

Identification of Cell Status via Simultaneous Multitarget Imaging Using Programmable Scanning Electrochemical Microscopy

A programmable multitarget-response electrochemical imaging technique was presented using scanning electrochemical microscopy (SECM) combined with a self-designed waveform. The potential waveform applied to the tip decreased the charging current caused by the potential switch, enhancing the signal-to-noise ratio. This programmable SECM (P-SECM) method was used to scan a metal strip for verifying its feasibility in feedback mode. Since it could achieve simultaneous multitarget imaging during one single imaging process, PC12 cells status was imaged and identified through three different molecules (FcMeOH, Ru(NH₃)₆³⁺, and oxygen). The FcMeOH image eliminated the error from cell height, and the Ru(NH₃)₆³⁺ image verified the change of membrane permeability. Moreover, the oxygen image demonstrated the bioactivity of the cell via its intensity of respiration. Combining information from these three molecules, the cell status could be determined accurately and also the error caused by time consumption with multiple scans in traditional SECM was eliminated.

Enhanced resolution of generator-collector studies of enzymatic structures by means of hydrodynamic scanning electrochemical microscopy

In this report, the effects of forced convection on scanning electrochemical microscopy (SECM) studies of enzymes in the context of the generator-collector mode (G/C mode) were investigated. Forced convection was generated via an electrical high precision stirrer integrated into the electrochemical cell. Circular spots of glucose oxidase were immobilized on a gold support serving as model substrate. The diffusion layer of enzymatically generated H₂O₂ was characterized recording probe scan curves (PSCs) in z-direction. Furthermore, the enzyme-modified surfaces were investigated via constant-height SECM imaging in feedback mode and in G/C mode. For methodical comparison all sets of experiments were performed in quiescent solution (conventional approach) and with forced convection, respectively. In contrast to a growing diffusion layer without forced convection by applying forced convection, a constant diffusion layer of produced H₂O₂ was observed. Hence, via hydrodynamic SECM time-independent images within a reasonable time scale of SECM measurements in G/C mode were enabled and their resolution was enhanced.

Correlating Live Cell Viability with Membrane Permeability Disruption Induced by Trivalent Chromium

Cr(III) is often regarded as a trace essential micronutrient that can be found in many dietary supplements due to its participation in blood glucose regulation. However, increased levels of exposure have been linked to adverse health effects in living organisms. Herein, scanning electrochemical microscopy (SECM) was used to detect variation in membrane permeability of single cells (T24) resulting from exposure to a trivalent Cr-salt, CrCl₃. By employing electrochemical mediators, ferrocenemethanol (FcMeOH) and ferrocenecarboxylic acid (FcCOO^-), initially semipermeable and impermeable, respectively, complementary information was obtained. Three-dimensional COMSOL finite element analysis simulations were successfully used to quantify the permeability coefficients of each mediator by matching experimental and simulated results. Depending on the concentration of Cr(III) administered, three regions of membrane response were detected. Following exposure to low concentrations (up to 500 μM Cr(III)), their permeability coefficients were comparable to that of control cells, 80 μm/s for FcMeOH and 0 μm/s for FcCOO^-. This was confirmed for both mediators. As the incubation concentrations were increased, the ability of FcMeOH to permeate the membrane decreased to a minimum of 17 μm/s at 7500 μM Cr(III), while FcCOO^- remained impermeable. At the highest examined concentrations, both mediators were found to demonstrate increased membrane permeability. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability studies were also conducted on Cr(III)-treated T24 cells to correlate the SECM findings with the toxicity effects of the metal. The viability experiments revealed a similar concentration-dependent trend to the SECM cell membrane permeability study.

Analysing single live cells by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) offers single live cell activities along its topography toward cellular physiology and pathology.

Quantifying microbial chatter: scanning electrochemical microscopy as a tool to study interactions in biofilms

Bacteria are often found in their natural habitats as spatially organized biofilm communities. While it is clear from recent work that the ability to organize into precise spatial structures is important for fitness of microbial communities, a significant gap exists in our understanding regarding the mechanisms bacteria use to adopt such physical distributions. Bacteria are highly social organisms that interact, and it is these interactions that have been proposed to be critical for establishing spatially structured communities. A primary means by which bacteria interact is via small, diffusible molecules including dedicated signals and metabolic by-products; however, quantitatively monitoring the production of these molecules in time and space with the micron-scale resolution required has been challenging. In this perspective, scanning electrochemical microscopy (SECM) is discussed as a powerful tool to study microbe-microbe interactions through the detection of small redox-active molecules. We highlight SECM as a means to quantify and spatially resolve the chemical mediators of bacterial interactions and begin to elucidate the mechanisms used by bacteria to regulate the emergent properties of biofilms.

Biological imaging with scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a powerful and versatile technique for visualizing the local electrochemical activity of a surface as an ultramicroelectrode tip is moved towards or over a sample of interest using precise positioning systems. In comparison with other scanning probe techniques, SECM not only enables topographical surface mapping but also gathers chemical information with high spatial resolution. Considerable progress has been made in the analysis of biological samples, including living cells and immobilized biomacromolecules such as enzymes, antibodies and DNA fragments. Moreover, combinations of SECM with comple-mentary analytical tools broadened its applicability and facilitated multi-functional analysis with extended life science capabilities. The aim of this review is to present a brief topical overview on recent applications of biological SECM, with particular emphasis on important technical improvements of this surface imaging technique, recommended applications and future trends.

Recent Advances in Scanning Electrochemical Microscopy for Biological Applications

Scanning electrochemical microscopy (SECM) is a chemical microscopy technique with high spatial resolution for imaging sample topography and mapping specific chemical species in liquid environments. With the development of smaller, more sensitive ultramicroelectrodes (UMEs) and more precise computer-controlled measurements, SECM has been widely used to study biological systems over the past three decades. Recent methodological breakthroughs have popularized SECM as a tool for investigating molecular-level chemical reactions. The most common applications include monitoring and analyzing the biological processes associated with enzymatic activity and DNA, and the physiological activity of living cells and other microorganisms. The present article first introduces the basic principles of SECM, followed by an updated review of the applications of SECM in biological studies on enzymes, DNA, proteins, and living cells. Particularly, the potential of SECM for investigating bacterial and biofilm activities is discussed.

Submicron probes for scanning electrochemical microscopy

To improve the spatial resolutions of scanning electrochemical microscopy (SECM) imaging, the laser-pulled submicron electrode fabrication method was explored in this work. Manual polishing of a laser-pulled Pt nanoelectrode exposed a Pt tip diameter of 250 nm with a ratio of the tip glass to exposed Pt disc (RG) of 30. This fabricated submicron probe was then utilized to study the electrochemical functionality of an independently addressable microband electrodes (IAME) sample using SECM. In the constant imaging mode of SECM, where the probe is scanned linearly across the sample at a fixed z position, SECM demonstrated higher resolution than that of the conventional micrometer electrodes when the feedback currents from the Pt and glass microbands were characterized. In addition, the depth scan imaging mode of SECM was also used to extract experimental horizontal line scans and probe approach curves for analysis. Three-dimensional (3D) simulations of the IAME–SECM probe experiments were explored for the first time to quantify the tip-to-sample distances, tilt angle of the sample (or electrode), and height of the Pt microbands. The experimentally characterized height was found to be similar to manufacturer specification (125 nm vs 110 nm). Furthermore, the more computationally demanding 3D simulation of the true IAME sample geometry (110 nm height of the Pt microbands) revealed minimal difference in feedback behaviours in comparison with the idealized flat geometry. The removal of this simulation complexity was proved to be sufficient for SECM analysis of the IAME sample by a 250 nm Pt probe, which greatly saves computation resources.

Nanostructured surfaces for analysis of anticancer drug and cell diagnosis based on electrochemical and SERS tools

Discovering new anticancer drugs and screening their efficacy requires a huge amount of resources and time-consuming processes. The development of fast, sensitive, and nondestructive methods for the in vitro and in vivo detection of anticancer drugs' effects and action mechanisms have been done to reduce the time and resources required to discover new anticancer drugs. For the in vitro and in vivo detection of the efficiency, distribution, and action mechanism of anticancer drugs, the applications of electrochemical techniques such as electrochemical cell chips and optical techniques such as surface-enhanced Raman spectroscopy (SERS) have been developed based on the nanostructured surface. Research focused on electrochemical cell chips and the SERS technique have been reviewed here; electrochemical cell chips based on nanostructured surfaces have been developed for the in vitro detection of cell viability and the evaluation of the effects of anticancer drugs, which showed the high capability to evaluate the cytotoxic effects of several chemicals at low concentrations. SERS technique based on the nanostructured surface have been used as label-free, simple, and nondestructive techniques for the in vitro and in vivo monitoring of the distribution, mechanism, and metabolism of different anticancer drugs at the cellular level. The use of electrochemical cell chips and the SERS technique based on the nanostructured surface should be good tools to detect the effects and action mechanisms of anticancer drugs.

Electrochemical recognition and quantification of cytochrome c expression in Bacillus subtilis and aerobe/anaerobe Escherichia coli using N,N,N',N'-tetramethyl-para-phenylene-diamine (TMPD)

Transferring the colorimetric oxidase test to electrochemistry: quantitative detection of bacteria by means of cytochrome c oxidase.

The colorimetric identification of pathogenic and non-pathogenic bacteria in cell culture is commonly performed using the redox mediator N,N,N′,N′-tetramethyl-para-phenylene-diamine (TMPD) in the so-called oxidase test, which indicates the presence of bacterial cytochrome c oxidases. The presented study demonstrates the ability of electrochemistry to employ TMPD to detect bacteria and quantify the activity of bacterial cytochrome c oxidases. Cyclic voltammetry studies and chronoamperometry measurements performed on the model organism Bacillus subtilis result in a turnover number, calculated for single bacteria. Furthermore, trace amounts of cytochrome c oxidases were revealed in aerobically cultured Escherichia coli, which to our knowledge no other technique is currently able to quantify in molecular biology. The reported technique could be applied to a variety of pathogenic bacteria and has the potential to be employed in future biosensing technology.

Sensing cisplatin-induced permeation of single live human bladder cancer cells by scanning electrochemical microscopy

Cisplatin is a widely used anti-cancer agent, which was believed to trigger apoptosis of cancer cells by forming DNA adducts. However, recent studies evidenced a cisplatin-induced extrinsic apoptotic pathway through interaction with plasma membranes. We present quantitative time-course imaging of cisplatin-induced permeation of ferrocenemethanol to single live human bladder cancer cells (T24) using scanning electrochemical microscopy (SECM). Simultaneous quantification of cellular topography and membrane permeability was realized by running SECM in the depth scan mode. It was demonstrated that the acute addition of cisplatin to the outer environment of T24 cells immediately induced membrane permeability change in 5 min, which indicated a loosened structure of the cellular membrane upon cisplatin dosage. The cisplatin-induced permeation of T24 cells might be a one-step action, an extrinsic mechanism, since the cell response was quick, and no continuous increase in the membrane permeability was observed. The time-lapse SECM depth scan method provided a simple and facile way of monitoring cisplatin-induced membrane permeability changes. Our study is anticipated to lead to a methodology of screening anti-cancer drugs through their interactions with live cells.

Electrochemical and photophysical behavior of 1-naphthol in benzyl-n-hexadecyldimethylammonium 1,4-bis(2-ethylhexyl)sulfosuccinate large unilamellar vesicles

The behavior of 1-naphthol and its partition process in LUVs formed from a new catanionic surfactant were studied by electrochemical and spectroscopic techniques.

Single-Cell Migration as Studied by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) was used to study the migration of single live head and neck cancer cells (SCC25). The newly developed graphite paste ultramicroelectrode (UME) showed significantly less fouling in comparison to a 10 μm Pt-UME and thus could be used to monitor and track the migration pattern of a single cell. We also used SECM probe scan curves to measure the morphology (height and diameter) of a single live cancer cell during cellular migration and determined these dimensions to be 11 ± 4 μm and 40 ± 10 μm, respectively. The migration study revealed that cells within the same cell line had a heterogeneous migration pattern (migration and stationary) with an estimated migration speed of 8 ± 3 μm/h. However, serum-starved synchronized cells of the same line were found to have a non-heterogeneous cellular migration pattern with a speed of 9 ± 3 μm/h. Thus, this non-invasive SECM-based technique could potentially be expanded to other cell lines to study cellular biomechanics for improved understanding of the structure-function relationship at the level of a single cell.

Advances in studies of nanoparticle–biomembrane interactions

Nanoparticles (NPs) are widely applied in nanomedicine and diagnostics based on the interactions between NPs and the basic barrier (biomembrane). Understanding the underlying mechanism of these interactions is important for enhancing their beneficial effects and avoiding potential nanotoxicity. Experimental, mathematical and numerical modeling techniques are involved in this field. This article reviews the state-of-the-art techniques in studies of NP–biomembrane interactions with a focus on each technology's advantages and disadvantages. The aim is to better understand the mechanism of NP–biomembrane interactions and provide significant guidance for various fields, such as nanomedicine and diagnosis.

A time course study of cadmium effect on membrane permeability of single human bladder cancer cells using scanning electrochemical microscopy

Cd(2+) is carcinogenic to both humans and experimental animals. We present quantitative time-course imaging of Cd(2+)-induced variation in the membrane permeability of single live human bladder cancer cells (T24) to ferrocenemethanol using scanning electrochemical microscopy (SECM). High temporal resolution combined with non-invasive nature renders a time-lapse SECM depth scan, a promising method to quantitatively investigate the effectiveness, kinetics, and mechanism of metal ions based on the responses of single live cells in real time. Under unstimulated conditions, T24 cells have constant membrane permeability to ferrocenemethanol of approximately 5.0×10(-5) m/s. When cadmium is added in-situ to T24 cells, the membrane permeability increases up to 3.5×10(-4) m/s, allowing more flux of ferrocenemethanol to the ultramicroelectrode tip. This suggests an increased spreading between the phospholipid heads in the cytoplasmic membrane. Membrane permeability might be used as a measure to probe cell status in practical intoxication cases. The methodology reported here can be applied to many other metals and their interactions with extracellular biomolecules, leading insights into cell physiology and pathobiology.

Redox competition and generation-collection modes based scanning electrochemical microscopy for the evaluation of immobilised glucose oxidase-catalysed reactions

Redox competition (RC-SECM) and generation-collection (GC-SECM) modes of scanning electrochemical microscopy were applied for the evaluation of a glucose oxidase (GOx)-modified non-conducting poly(methyl methacrylate) surface.

An electrochemical surface plasmon resonance imaging system targeting cell analysis

This paper presents an electrochemical-surface plasmon resonance imaging (EC-SPRI) system, enabling the characterization of optical and electrical properties of cells, simultaneously. The developed surface plasmon resonance (SPR) imaging system was capable of imaging micro cavities with a dimension of 10 μm × 10 μm and differentiated glycerol solutions with a group of refractive indices (RIs). Furthermore, the EC-SPRI system was used to image A549 cells, suggesting corresponding RI and morphology changes during the cell death process. In the end, electrochemical and SPR methods were used in combination, recording oxidation peaks of A549 cells in the cyclic voltage curves and SPR response unit increase, simultaneously.

Recent advances in high resolution scanning electrochemical microscopy of living cells--a review

This review discusses advances in the field of high resolution scanning electrochemical microscopy (HR-SECM) and scanning ion conductance microscopy (SICM) to study living cells. Relevant references from the advent of this technique in the late 1980s to most recent contributions in 2012 are presented with special discussion on high resolution images. A clear progress especially within the last 5 years can be seen in the field of HR-SECM. Furthermore, we also concentrate on the intrinsic properties of SECM imaging techniques e.g. different modes of image acquisition, their advantages and disadvantages in imaging living cells and strategies for further enhancement of image resolution, etc. Some of the recent advances of SECM in nanoimaging have also been discussed which may have potential applications in high resolution imaging of cellular processes.