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Abstract: Synchronization of cell spreading is valuable for the study of molecular events involved in the formation of adhesive contacts with the substrate. At a low ionic concentration (0.17mM) Dictyostelium discoideum cells levitate over negatively charged surfaces due to electrostatic repulsion. First, a two-chamber device, divided by a porous membrane, allows to quickly increase the ionic concentration around the levitating cells. In this way, a good synchronization was obtained, the onsets of cell spreading being separated by less than 5s. Secondly applying a high potential pulse (2.5V/Ref, 0.1s) to an Indium Tin Oxide surface attracts the cells toward the surface where they synchronously spread as monitored by LimE Δcoil-GFP. During spreading, actin polymerizes in series of active spots. On average, the first spot appears 8–11s after the electric pulse and the next ones appear regularly, separated by about 10s. Synchronized actin-polymerization activity continues for 40s. Using an electric pulse to control the exact time point at which cells contact the surface has allowed for the first time to quantify the cellular response time for actin polymerization. Electrochemical synchronization is therefore a valuable tool to study intracellular responses to contact. [ABSTRACT FROM AUTHOR]

Abstract: Accuracy of kinetics characterization from SECM feedback experiments is carefully discussed. The experimental conditions that lead to the best accuracy are thus detailed on the basis on theoretical results. A recently published experimental study is also used to illustrate the discussion. Three different experimental characteristics of the SECM data acquisition are examined and discussed in this work: the geometrical characteristics of the microdisk tip, the tip-substrate distance range and the influence of an error on the zero tip-substrate distance. The best experimental conditions are encountered with the combination of results coming from approach curves with tips having Rg values larger than 10 on the 0.1–2 tip-substrate distance range and different radius, leading to a dimensionless kinetic parameter in the 0.10–1.8 range and through fit procedure with two adjustable parameters considering the zero tip-substrate distance as unknown. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of 4-nitrobenzenediazonium tetrafluoroborate (NBD) in acidic aqueous solution was investigated by scanning electrochemical microscopy (SECM) on polycrystalline gold and glassy carbon (GC) substrates. The feedback mode of SECM was used to study the local properties of each substrate before and after immersion in the aryldiazonium solution, by performing approach curves with two redox mediators, and . The fitting of the approach curves with analytical approximate equation was used to evaluate the apparent heterogeneous rate constant k for redox system at NBD-adsorbed GC (k =2.6×10−4 cms−1). [Copyright &y& Elsevier]