We developed a highly sensitive oxygen consumption scanning microscopy system using platinized platinum disc microelectrodes. The system is capable of reliably detecting single-cell respiration, responding to classical regulators of mitochondrial oxygen consumption activity as expected. Comparisons with commercial multi-cell oxygen detection systems show that the system has comparable errors (if not smaller), with the advantage of being able to monitor inter and intra-cell heterogeneity in oxygen consumption characteristics. Our results uncover heterogeneous oxygen consumption characteristics between cells and within the same cell´s microenvironments. Single Cell Oxygen Mapping (SCOM) is thus capable of reliably studying mitochondrial oxygen consumption characteristics and heterogeneity at a single-cell level.Because mitochondrial oxidative phosphorylation is the end-point of most metabolic processes, monitoring oxygen consumption is an effective manner to continuously and non-invasively evaluate energy metabolism in different cell types. Indeed, high-resolution commercial systems have been developed to monitor oxygen consumption in suspended biological samples, using Clark-type electrodes 1-3 , and plated cultured cells 4 , using fluorescent probes. These systems have been successfully used to uncover many different metabolic conditions, with applications as varied as in inherited mitochondrial diseases, inflammation, diabetes, neuroscience and aging [5][6][7][8][9] . Using specific inhibitors, oxygen consumption experiments can determine basal and maximal mitochondrial respiratory capacity, ATP-linked processes, non-ATP-producing respiration (thermogenesis and non-mitochondrial respiration) and estimate substrates used, among other parameters 4, 10 .However, these techniques present the caveat of detecting only bulk oxygen consumption of the media in which the cells are suspended. They are therefore unable to detect heterogeneity of metabolic characteristics among different individual cells in the same culture, and cannot detect characteristics of this consumption within different areas of a single cell. To date, evaluations of mitochondrial metabolic heterogeneity within and among individual cells have mostly been conducted using fluorescent microscopy and probes for mitochondrial inner membrane potentials. Unfortunately, these evaluations are not quantitative and marred by many artifacts including phototoxicity, influence of plasma membrane potentials, artifacts due to aggregation and changes in mitochondrial mass and morphology 11,12 .We thus believe the area would greatly benefit from the development of single cell oxygen consumption techniques. Different techniques have been used to acquire topographical information with high spatial resolution, including atomic force microscopy (AFM), scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM), which is highly valuable in measurements of local electrochemical activity at interfaces [13][14][15][16] . Indeed, SECM has been used in th...

Anatase TiO 2 is a promising material for Liion (Li + ) batteries with fast charging capability. However, Li + (de)intercalation dynamics in TiO 2 remain elusive and reported diffusivities span many orders of magnitude. Here, we develop a smart protocol for scanning electrochemical cell microscopy (SECCM) with in situ optical microscopy (OM) to enable the highthroughput charge/discharge analysis of single TiO 2 nanoparticle clusters. Directly probing active nanoparticles revealed that TiO 2 with a size of � 50 nm can store over 30 % of the theoretical capacity at an extremely fast charge/discharge rate of � 100 C. This finding of fast Li + storage in TiO 2 particles strengthens its potential for fast-charging batteries. More generally, smart SECCM-OM should find wide applications for high-throughput electrochemical screening of nanostructured materials.

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O2 and H2 and electrochemical conversion of CO2. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).

Electrochemical techniques offer high temporal resolution for studying the dynamics of electroactive species at samples of interest. To monitor fastest concentration changes, a micro- or nanoelectrode is accurately positioned in the vicinity of a sample surface. Using a microelectrode array, it is even possible to investigate several sites simultaneously and to obtain an instantaneous image of local dynamics. However, the spatial resolution is limited by the minimal electrode size required in order to contact the electrodes. To provide a remedy, we introduce the concept of scanning bipolar electrochemical microscopy and the corresponding experimental system. This technique allows precise positioning of a wireless scanning bipolar electrode to convert spatially heterogeneous concentrations of the analyte of interest into an electrochemiluminescence map of the sample reactivity. After elucidating the working principle by recording bipolar line and array scans, a bipolar electrode array is positioned at the site of interest to record an electrochemical image of the localized release of analyte molecules.

The solid‐electrolyte interphase (SEI) plays a key role in the stability of lithium‐ion batteries as the SEI prevents the continuous degradation of the electrolyte at the anode. The SEI acts as an insulating layer for electron transfer, still allowing the ionic flux through the layer. We combine the feedback and multi‐frequency alternating‐current modes of scanning electrochemical microscopy (SECM) for the first time to assess quantitatively the local electronic and ionic properties of the SEI varying the SEI formation conditions and the used electrolytes in the field of Li‐ion batteries (LIB). Correlations between the electronic and ionic properties of the resulting SEI on a model Cu electrode demonstrates the unique feasibility of the proposed strategy to provide the two essential properties of an SEI: ionic and electronic conductivity in dependence on the formation conditions, which is anticipated to exhibit a significant impact on the field of LIBs.

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The fabrication of a gold microelectrode modified with iridium oxide film (IrOx) and its use as tip with a dual function in SECM experiments is reported. The defective structure of the coating onto the microelectrode surface was used as strategy to combine the advantages of both amperometric (for current‐distance determination) and potentiometric (for pH sensing) SECM operation modes. Approach curves, using oxygen and hexaammineruthenium(III) as redox mediators, were obtained without significant loss of the performance and reproducibility of the potentiometric pH response. This allowed the precise positioning of the proposed tip above a substrate in SECM experiments and, subsequently, to monitor pH at the substrate surface. The IrOx modified microelectrode was applied successfully in SECM experiments involving the local proton consumption during the nitrate reduction at a copper cathode surface.

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