Dielectrophoresis (DEP) offers many advantages over conventional cell assays such as flow cytometry and patch clamp techniques for assessing cell electrophysiology as a marker for cancer studies and drug interaction assessment. However, despite the advantages offered by DEP analysis, uptake has been low, remaining largely in the academic arena, due to the process of analysis being time-consuming, laborious, and ultimately allowing only serial analysis on small numbers of cells. In this paper we describe a new method of performing DEP analysis based on laminate manufacturing methods. These use a three-dimensional “well” structure, similar in size and pitch to conventional microtiter well plates, but offer electrodes along the inner surface to allow easy measurement of cell properties through the whole population. The result can then be determined rapidly using a conventional well-plate reader. The nature of the device means that many electrodes, each containing a separate sample, can be tested in parallel, while the mode of observation means that analysis can be combined with simultaneous measurement of conventional fluorimetric well-based assays. Here we benchmark the device against standard DEP assays, then show how such a device can be used to (a) rapidly determine the effects both of ion channel blockers on cancer cells and antibiotics on bacteria and (b) determine the properties of multiple subpopulations of cells within a well simultaneously.

Introduction

Fast field cycling (FFC) nuclear magnetic resonance (NMR) is applied to probe the slow dynamics of liquid molecules imbibed in porous catalysts. The FFC measurements are used to determine surface diffusion correlation and residence times that provide information on the molecular dynamics of surface adsorbed species. The longitudinal relaxation time T 1 dispersion curves reveal biphasic diffusion of adsorbed water that we attribute to the presence of "strongly bound" and "weakly bound" molecules. FFC measurements of organic liquids (2-butanone, 2-propanol) do not show such behavior. These observations agree with molecular dynamics simulations. The frequency dependence of the relaxation time ratio T 1 /T 2 is also considered; it is demonstrated that T 1 /T 2 remains a valid indicator of adsorption energy regardless of the field strength at which the measurement is taken in the range B 0 = 0.1 mT to 0.23 T. ■ INTRODUCTIONUnderstanding the interactions between adsorbate and surface is central to studies of heterogeneous catalysis. 1−9 Knowledge of surface activity is essential if existing processes are to be optimized and new catalyst design approached in a rational manner. 8 Liquid-phase catalysis is an active research topic with regard to the production of fuels and chemical commodities from sustainable sources. 10,11 In these catalytic processes, multiple components are present in the liquid phase, either as reactant species adsorbing competitively or as a combination of reactant, intermediate, and product species, as well as any solvent species present. Knowledge of the strength of interaction of each possible adsorbate with the catalyst surface and the influence of each component upon the adsorption of the others is a crucial step toward understanding the catalytic reaction system. Solvents can play a key role in catalyzed reactions with catalytic activity and selectivity depending on the choice of solvent. 12−14 In general, hydrogenation reactions represent an important class of catalytic transformations in both gas 15−19 and liquid phase, with solvent effects observed in the latter. 20−26 In previous work, we have considered the role of adsorption on palladium and ruthenium catalysts in the context of 2-butanone hydrogenation. 27,28 The hydrogenation of 2-butanone over the supported metal has been studied previously employing a mixture of 2-propanol and water as solvents. These studies revealed that solvent composition influences the reaction rate. Specifically, the rate of hydrogenation was seen to increase as the water mole fraction increased. 28 However, while it is recognized that the presence of water can facilitate the hydrogenation of carbonyl species, 20 reports on the effect of water on catalytic activity, in general, vary. In other hydrogenation reactions, water has been observed to reversibly increase 29−31 or decrease activity, 31 or result in irreversible deactivation of the catalyst. 31−34 The aim of the present work is to capture the extent to which nuclear magnetic resonance (NMR) fast field ...

Fast-field cycling magnetic resonance imaging FFC-MRI Earth-field MRI Pre-polarised MRI Free-radical imaging Magnetisation-transfer contrast Mots-clés : IRM en champ cyclé FFC-IRM IRM en champ magnétique terrestre IRM prépolarisée Imagerie par radicaux libres Contraste par transfert de magnetisationMagnetic resonance imaging (MRI) and fast field-cycling (FFC) NMR are both welldeveloped methods. The combination of these techniques, namely fast field-cycling magnetic resonance imaging (FFC-MRI) is much less well-known. Nevertheless, FFC-MRI has a number of significant applications and advantages over conventional techniques, and is being pursued in a number of laboratories. This article reviews the progress in FFC-MRI over the last two decades, particularly in the areas of Earth's field and prepolarised MRI, as well as free radical imaging using field-cycling Overhauser MRI. Different approaches to magnet design for FFC-MRI are also described. The paper then goes on to discuss recent techniques and applications of FFC-MRI, including protein measurement via quadrupolar cross-relaxation, contrast agent studies, localised relaxometry and FFC-MRI with magnetisation-transfer contrast. r é s u m é L'imagerie par Résonance Magnétique (IRM, ou MRI en anglais) et la RMN avec cyclage de champ rapide (« fast field cycling », FFC) sont toutes deux des méthodes bien développées. La combinaison de ces techniques, c'est-à-dire l'imagerie par résonance magnétique avec cyclage de champ rapide (FFC-MRI en anglais) est beaucoup moins bien connue. Cependant, la FFC-MRI a un nombre d'applications et d'avantages significatifs par rapport aux techniques conventionnelles, et son étude est poursuivie dans un certain nombre de laboratoires. Cet article passe en revue les progrès de la FFC-MRI au cours des deux dernières décennies, en particulier dans les domaines de l'imagerie en champ terrestre avec pré-polarisation, de même que l'imagerie des radicaux libres en utilisant la FFC-MRI avec effet Overhauser. Diverses approches à la conception des aimants pour FFC-MRI sont également décrites. L'article continue en discutant des techniques et applications récentes de la FFC-MRI, telles que la mesure des protéines par relaxation croisée quadrupolaire, les études d'agents de contraste, la relaxométrie localisée et la FFC-MRI avec contraste par transfert d'aimantation.

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