No description available.

This thesis is prepared for the examination of the Master of Philosophy degree from University College London. It provides fundamental knowledge in the field of bio-impedance, including basic concepts, measurement techniques and derived various applications for improving health care options for the wide community of human being. The thesis is organized into six chapters. Chapter One starts the thesis by introducing the concept of bio-impedance. Some representative designs of measurement cells and probes are briefly presented and classified into two categories for in vivo and in vitro application; so as to provide the parameter reference for designing an integrated version of bio-impedance measurement system (BMS). In addition, a brief mathematic foundation is included to explain the signal path of bio-impedance measurement system. A few applications of bio- impedance techniques, including the Electrical Impedance Tomography (EIT) are discussed. This chapter concludes with the limitation of BMS implemented using discrete components and proposes an integrated version of BMS to be applicable for increasingly challenging needs of health care service. This chapter also defines the system specification of BMS, such as operating frequencies, input dynamic range, and safety voltage/current requirement. Chapter Two investigates the origins of bio-impedance by studying the biological structure of a cell and its passive electrical parameter, such as at macro level impedance, and at the micro level, permitivity and conductivity. Chapter Three reviews various macro level electrical models of biological tissue, such as finger, leg, nerve etc, proposed by previous researchers. The disagreement of various electrical modelling presents a big challenge for fair comparison of various BMS performance. Chapter four reviews four categories of fundamental techniques underlying various BMS structures. The current/voltage technique is preferred by most current designs. Chapter five focuses the design of a monolithic instrumentation amplifier (in-amps) for BMS. Formulas of various critical system parameters, such as Gain/Bandwidth, Noise, Input/output impedance are derived. Schematics of amplifier are implemented in Cadence Virtuoso custom design platform with AMS 0.35μm technology. Simulation results, which proves the design meets specification are summarised in the end. Chapter Six ends the entire research thesis by summarising achievements of this work. In addition, some possible future work for the project are suggested and discussed.

The roots of this study stem from the applied sciences of microbiology and electrochemistry to form the exciting new field of bio-electrochemistry. Our aim here being the application of bioelectrochemical processes for social and environmental value in toxic metal ion remediation and recovery from the discharge of aqueous mine and industrial effluents. This within a broader vision of reducing the present burden caused by industrial and mining anthropogenic activity on the planet we inhabit. These processes we have explored within a green chemistry philosophy with the application of chemical engineering principles. Our aims being (i) to further the scientific state of art and (ii) conceptualize the feasible engineering of novel metal remediation strategies, with the lucrative application of bacterial cells as green “nanofactories” and recovery of metallic biogenic nanoparticles with application in the ever growing field of nanotechnology. The proof of principle has been evaluated with a systematic study of Au3+, Co2+ and Fe3+ metallic cationic species (Co < 500 ppm) dissolved in acidic (pH < 3) aqueous electrolytes and their removal by microbiological (chapter 3) and bioelectrochemical (chapter 4) processes. Electrochemical remediation as described by electronation charge transfer at an electrified interface for various potentials causes the electrodeposition of metal ions upon electrode surfaces and hence separation by phase transformation. Of note, base cations such Co2+ and Fe3+ co-deposited with the evolution of hydrogen gas could be applied as electron donors for chemolithotrophic bacteria as part of dissimilatory respiration. Microbial biosorption of metal ions by means of ionized groups located on the outer membrane of the outer lipopolysaccharide leaf of gram negative bacteria, with some evidence of bio-reduction via dissimilatory and redox resistance mechanisms, with biogenic nanoparticles produced as a consequence. Bio-electrochemistry formed by the collaboration of these two processes where electroactive bacteria such as that of the Shewanella genus are known to respire by the application of cathodic currents directly via bio-nanowires or indirectly using in-situ electron mediators or in-situ hydrogen production. The effects of bacteria on electronation thermodynamics were investigated in chapter 4 with observed positive shifts in reversible potentials (Er) for AuCl3- electrodeposition.

The inactivation of the calcium permeability in Helix aspersa neurones was studied in relation to [Ca]. Injection of calcium ions was shown to reduce the voltage activated calcium current by increasing [Ca]. This was proved to be by a process of inactivation of the calcium current, rather than a direct effect of increased [Ca] on the driving force for calcium across the membrane. [Ca] was measured using ion sensitive electrodes, and a mean resting level of 2.66+/-0.65 x 10-7K was obtained. The inactivation of the calcium current was found to fit 1 to 1 binding between calcium and the receptor responsible for inactivation giving a Kd, of 4.8 x 10-7K. A number of techniques were used to influence the intracellular cAMP concentrations of the snail neurones in an attempt to isolate some form of metabolic control of the calcium permeability. However, no consistent responses could be obtained. The patch clamp technique was used to look at the unitary current in frog skeletal muscle. Membrane vesicles formed from the sarcolemma by enzyme treatment, were found to reduce the number of problems associated with the use of the technique on intact muscle fibres. Sodium and delayed rectifier potassium channels were identified in the vesicles, having conductances in the range 12-15pS and l6-24pS, for the two types of current. The kinetics of the sodium channels in the vesicles were found to be slightly slower than those reported for the intact frog skeletal muscle. Kowever, they could still be fitted to the m h model of Odgkin and Luxley. Studies of the kinetics of the delayed rectifier potassium channels suggested a model for the channel different from the four-closed state system proposed by odgkin and luxley. Finally, experiments were performed on snail neurons in order to observe the unitary calcium activated potassium currents.

This research undertaken involved designing, fabricating and testing of a microfiuidic peR micro device with real-time electrochemical detection. The aim was to provide an analytical device which could lower the cost and the time taken for running DNA amplification. The later addition of automated sample handling and detection would thereby reduce the time taken and consequently the overall cost. The real-time electrochemical detection utilised an electrochemical assay for the detection of DNA invented by Molecular Sensing Ltd. It used a single strand ferrocenylated probe DNA molecule which could be detected with an electrochemical cell. The integration of an electrochemical cell was a key feature of this work, along with the immobilisation of the Taq polymerase at its working temperature. Taq polymerase enzyme and T7 polymerase enzyme were immobilised on to microspheres. Taq polymerase was immobilised in four ways and T7 polymerase was immobilised in only one method. After immobilisation the enzymes were unable to amplify DNA within peR experiments. Microfiuidic peR devices, which incorporate the above two features, were designed and fabricated. 3 basic ideas of devices were investigated, fiowthrough, straight line and cyclic triangle device. All the devices had fundamental problems which inhibited there ability to successfully amplify DNA. An electrochemical assay was used within a microfiuidic device with internal electrochemical detection, which utilised a filter to bring about sequence specific DNA detection. Using biotinylated complementary probe DNA attached to streptavidin coated beads to hybridise to the sample DNA. This device incorporated a solid phase extraction and clean up step as well as producing sequence specific DNA detection.

Etant donné leur implication dans de nombreux processus biochimiques, les ARN sont maintenant considérés comme des cibles thérapeutiques très prometteuses. Cependant, nos connaissances limitées concernant les phénomènes d'interaction entre les ARN et de petites molécules, compliquent l'élaboration de nouveaux ligands (ou médicaments), capables de reconnaître sélectivement une structure complexe d'ARN. En absence de toute approche rationnelle, une stratégie de criblage pourrait permettre de mieux comprendre ces phénomènes de reconnaissance. Cette thèse porte sur la mise au point d'une méthode électrochimique, simple, adaptée pour du criblage haut-débit et permettant de détecter et de quantifier les interactions ARN/ligands. Le principe de la méthode repose sur la différence de coefficient de diffusion qui existe entre la forme libre d'un ligand possédant des propriétés redox et sa forme complexée à l'ARN. Cette stratégie de détection par voie électrochimique présente comme avantages d'être peu coûteuse, rapide, simple d'utilisation, adaptée pour du criblage haut-débit de molécules et utilisable dans de faibles volumes. Cette méthodologie a été utilisée pour caractériser la formation d'un complexe entre un analogue d'aminoglycoside porteur d'un groupe ferocene et une séquence d'ARNr 16S23. De plus, des expériences de compétition entre le complexe ARN/ligand redox et des aminoglycosides non modifiées permettent d'étendre la méthode à la détermination de constantes de dissociation (KD) pour des molécules non marquées en phase homogène. Ces expériences de compétition pourront être généralisées pour mesurer le KD de librairies de molécules, permettant ainsi de trouver de meilleurs ligands d'ARN. / RNA molecules play a major role in various biochemical processes and they are now considered as an important drug target. However, our limited understanding of the interactions occurring between small molecules and RNA complicate the search for new ligands (or drugs) with improved specific interaction and binding to elaborated RNA structures. In the absence of any rational approach, a screening strategy could shed light on the ligand/RNA interactions. In this thesis, we describe a simple electrochemical approach allowing for high-throughput detection and quantification of small molecule/RNA interactions. The principle of the method relies on the difference of diffusion rates between a redoxmolecular probe free or bound to its RNA target and thus to the ability to more easily electrochemically detect the forme rover the latter in a homogenous solution. This electrochemical detection strategy has the advantages of being affordable,fast, easy to use, sensitive and well-adapted to a high-throughput screening strategy in small volume samples. This methodology was used to characterize the binding of an aminoglycoside analog bearing a ferocenyl group to the ribosomal RNA fragment (rRNA 16S23). Furthermore, competitive binding of unlabelled aminoglycosides on theRNA/electrochemical probe complex allowed us to evaluate their dissociation constants (KD). These competitive experiments could further be generalized to measure KD values for libraries of molecules, which could help to find better RNA ligands.

Électroporation (EP) est une technique utilisée pour affecter l’intégrité des membranes cellulaires de plasma et/ou organites internes, conséquence de l’application d’un champ électrique d’énergie suffisante, dépendant de son intensité et sa durée. Il a été montré in- directement par de nombreuses études expérimentales et in-silico que ce phénomène résulte de la perméabilisation de la membrane par la formation pores aqueux. L’EP permet ainsi la vectorisation de molécules normalement non perméantes. Les applications de l’EP vont de l’électrochimiothérapie, à la vaccination à ADN. Les impulsions électriques utilisées dans l’EP sont classées en deux familles: Les msPEF dont la longueur des impulsions est de l’ordre de la microseconde et l’amplitude de l’ordre de quelques kV/cm. Ils affectent principalement la membrane cellulaire plasmique. Les nsPEFs d’intensité de MV/m de durée de l’ordre de la nanoseconde, ceux eux sont capables de perméabiliser organites internes ainsi que la membrane plasmique et présentent l’avantage d’éviter les effets thermiques indésirables. Les simulations de dynamique moléculaire (DM) qui permettent la description atomique, de la structure de la membrane et de son interaction avec la solution environnante, constituent un appui précieux aux résultats expérimentaux. Plusieurs études utilisant la DM été consacrées à décrire certains des aspects de l’EP (par exemple la formation de pores, leur évolution, le rôle de l’eau et des groupes de tête lipidiques, ...) néanmoins des questions en suspens restent inexplorées : • Comment la composition de la membrane affecte le seuil d’EP ? • Quelles sont la morphologie, la taille et la conductance des pores formés ? • Quels sont le mécanisme et l’échelle de temps de translocation de petites molécules à travers ces électropores ? • Y-a-t-il une différence notoire entre les effets des msPEFs et des nsPEFs ? Dans le cadre de ce travail, en utilisant des simulations de DM nous avons abordé ces questions pertinentes. Nous avons quantifié le seuil d’EP de bicouches lipidiques contenant des concentrations croissantes de cholestérol utilisant des protocoles qui miment les deux modes types de pulses nsPEFs et msPEFs. Les résultats obtenus indiquent que dans les deux cas les modèles de membranes à concentration en cholestérol croissante, nécessitent un voltage transmembranaire plus élevé pour perméabiliser la bicouche lipidique. Nous avons développé une procédure, mimant l’effet des msPEFs en adéquation avec les expériences, qui permet de stabiliser les voltages appliqués à la membrane suffisamment longtemps pour déterminer la dimension des pores, leur conductance et sélectivité ionique. Nous avons utilisé le même protocole pour étudier le transport de petites molécules chargées, utilisés dans l’administration de médicaments, et comparé nos résultats avec des études similaires menées dans des conditions nsPEFs. Nous avons montré que le transport assisté par EP a lieu dans la même échelle de temps (ns) que sous nsPEFs. Bien que les nsPEF ont l’avantage d’affecter les membranes cellulaires et celles des organites internes, la possibilité d’exploiter de telles impulsions pour la vectorisation de médicaments est encore en cours d’étude, car la capacité à fournir de manière fiable à des échantillons «biologiques» ces impulsions intenses ultra-courtes n’est pas trivial. Une attention particulière doit être accordée à la conception de micro-chambres afin de réaliser un dispositif à large bande passante afin de transmettre sans atténuation et distorsion les pulses ns, qui sont caractérisés par une grandes composante spectrale, jusqu’à GHz. Une partie importante de cette thèse mené en cotutelle, a été consacrée à la conception théorique (utilisant la Méthode des éléments Finis) d’un dispositif d’exposition, basé sur des systèmes de propagations de micro-ondes, capable de délivrer des impulsions aussi courtes que la ns avec des temps de monté et de chute de 0,5 ns / Electroporation (EP) is a technique used to affect the integrity of plasma cell membranes and/or internal organelles, consequence of the application of an external pulsed electric field of sufficient energy content, tuned by its strength and duration. It is proven by extensive indirect experimental and in silico evidences that this phenomenon results in the permeabilization of membrane structures by aqueous pores, allowing the transport of poorly- or non-permeant molecules, e.g. salts, ions, genetic material, and any other small solutes present. Applications of the techniques range from electrochemoterapy DNA vaccination and gene regulation. The electric pulses used in EP are categorized in two main families: msPEF, the length of the pulses is in the µs- ms scale and the amplitude in the order of kV/cm, their effect takes place mainly at the plasma cell membrane of cells; nsPEFs, higher magnitude (MV/m) over ns time scale, they act are able to permeabilize internal organelles as well as the plasma cell membrane, presenting the advantage of avoiding undesired thermal effects. Molecular dynamics simulations allow the microscopic description, with atomic resolution, of the membrane structure and its interaction with the surrounding solution, providing a substantial support to experimental findings. A considerable amount of work have been devoted to describe some of the aspects of EP using MD, (e.g. the pore formation, its evolution and reseal, the role of water and of lipid headgroups, …) nevertheless outstanding questions remain unexplored: • How does the composition of the bilayer affect the EP threshold? • What are the morphology, size and conductance of pores formed? • What are the mechanisms and time scales of translocation of small molecules through the electropores? • Is there any difference when modeling nsPEFs and msPEFs? As part of the present work, using MD simulations and comparing our results to other findings from our group, we addressed some relevant questions. We quantified the EP threshold of libid bilayes for the increasing concentration of cholesterol (0, 20, 30, 50 mol %) when the two protocol to model nsPEFs and msPEFs are exploited. The results obtained applying the two approaches indicate that in both cases an increase in cholesterol concentration requires a higher transmembrane voltage to porate the membrane bilayer. We developed a procedure, mimicking msPEFs, to stabilize electropores under different transmembrane voltages in mechanical condition similar to experiments for a time long enough to determine the pore dimension, its conductance and selectivity to ion species. We employed the same method to investigate the transport of small charged molecules, used in drug delivery, comparing our findings with similar studies conducted under nsPEFs conditions with the attempt to rationalize the molecular uptake. Interestingly we found that that the dynamic of the transport process takes place in the same time scale (nanosecond) that for nsPEFs. Despite the fact that nsPEFs have the advantage to affect both cell membranes and internal organelles and to further reduce thermal effects, the possibility to exploit nsPEFs for drug delivery is an ongoing research since the ability to reliably deliver to biological loads these ultra-short intense pulses is not trivial. Particular attention must be paid in the design of microchambers to realize a broadband devices to transmit without attenuation and distortion nsPEF, which exhibit large spectral components, i.e. spanning from MHz up to GHz. An important part of the current work has been devoted to the design (with Finite Element Method) of an exposure device, based on microwave propagating systems, able to deliver pulses down to 1 ns with rise and fall time of 0.5 ns

Cette thèse décrit différentes stratégies pour co-immobiliser au sein d'un film sol-gel une déhydrogénase, le cofacteur NAD+/NADH et un système pour régénérer électrochimiquement ce cofacteur. L'immobilisation de la déshydrogénase dans la matrice sol-gel a été obtenue en utilisant un polyélectrolyte positivement chargé comme additif dans le sol de départ. Le film peut être déposé par les procédés d'évaporation ou d'électrogénération, permettant alors la fonctionnalisation d'électrodes d'or macroporeuses. La diaphorase a également pu être co-encapsulée pour la régénération du cofacteur NAD+. L'immobilisation du cofacteur a ensuite été obtenue par couplage chimique du NAD+ avec le groupement époxy du glycidoxypropylsilane avant formation du film. Plusieurs stratégies d'immobilisation du médiateur électrochimique ont alors été étudiées avec succès. Les espèces de type ferrocène ou des complexes d'osmium(III) peuvent être incorporées dans la matrice sol-gel par encapsulation de polymères portant ces médiateurs (Fc-PEI et polymère d'osmium) ou par co-condensation avec un ferrocène fonctionnalisé par un groupement silane. Finalement d'autres stratégies ont été étudiées basées sur la fonctionnalisation de nanotubes de carbone par un traitement micro-onde, par électropolymérisation du vert de méthylène, ou par recouvrement par un polymère de type acrylate portant des complexes d'osmium(III). L'électrogénération d'une couche mince sol-gel servant à immobiliser les protéines et le cofacteur à la surface des nanotubes fonctionnalisés par le polymère d'osmium(III) a alors permis d'observer une réponse électrocatalytique de stabilité remarquable. / In this thesis, the research work was focused on designing functional layers based on silica sol-gel thin films to co-immobilize dehydrogenase, cofactor and electron mediator to get the most highly active systems. Immobilization of dehydrogenase in an active form in a sol-gel matrix was obtained by using a positively-charged polyelectrolyte as additive in the starting sol. The optimal sol can be deposited by evaporation or by electrodeposition and was successfully deposited in macroporous electrodes. The immobilization of the cofactor was investigated by simple entrapment, adsorption to carbon nanotube (CNTs), encapsulation of NAD+ chemically attached to dextran(NAD-dextran), and by in-situ coupling with glycidoxypropyltrimethoxysilane (GPS). The last approach allowed stable immobilization of the cofactor. Several mediators (Fc-PEI, Fc-Silane or Osmium polymer) were successfully co-immobilized with dehydrogenase and cofactor in the sol-gel matrix deposited by drop-coating. However, such co-immobilization did not operate in the electrogenerated sol-gel films. The strategies based on CNTs for mediator immobilization were finally developed. They include (1) micro-wave treatment (MWCNTs-µW), (2) electrochemical deposition of poly(methylene green) (MWCNTs-PMG), and (3) wrapping by osmium(III) polymer (MWCNTs-Os). MWCNTs-Os has been the only system that was successfully combined with sol-gel electrodeposition for co-immobilization of dehydrogenase and cofactor.

Nous avons cherché dans ce travail à élaborer un biofilm artificiel électroactif dans le but de promouvoir les réactions de transfert extracellulaire d’électrons (EET) en reconstituant artificiellement un biofilm en présence de matériaux exogènes. Un matériau composite auto-assemblé constitué de cellules bactériennes (Shewanella oneidensis), de nanotubes de carbone et de cytochromes c exogènes (issue de cellules de cœur de bœuf) a été tout d’abord proposé. Le processus d’auto-assemblage a été étudié par diffusion de lumière dynamique, microscopie électronique à balayage et spectroscopie Raman. Ces analyses ont mis en évidence l’importance du cytochrome exogène dans l’assemblage et l’organisation du matériau. La viabilité bactérienne a été étudiée et l’activité métabolique a été caractérisée par électrochimie. Les courants à l’anode étaient 10 et 4 fois plus importants avec ce biofilm artificiel (0,027 A m-2) qu’avec les électrodes modifiées par les bactéries seules (0,003 A m-2) ou associées au cytochrome c (0,007 A m-2). Le biofilm artificiel a été testé en substituant S. oneidensis par Pseudomonas fluorescens, produisant un courant d’oxydation lors de l’ajout de 1,5 mM de glucose. Le cytochrome c possède, outre son rôle structurant, une activité de navette à électrons. Son potentiel redox, 254 mV (vs NHE), était adapté à l’oxydation du formiate mais inadapté à la réduction du fumarate. Pour cette raison, il a été substitué par d’autres cytochromes (c3DvH, c7Da, c553DvH, c3DdN ou c3Dg) possédant des potentiels redox plus bas, de 20 mV à -400 mV. Ces cytochromes variaient aussi au niveau de leur charge à pH neutre, permettant de valider l’importance des forces électrostatiques dans l’assemblage du biocomposite. Les résultats optimaux obtenus avec c3DvH et c7Da ont montré l’importance du potentiel redox des éléments exogènes pour l’EET. Nous avons ensuite remplacé le cytochrome c par la protamine. Cette protéine non électroactive a permis l’assemblage du biocomposite tout en maintenant les transferts directs d’électrons entre les bactéries et les différents nanomatériaux testés. Les optimisations ont permis d’atteindre des courants cathodiques de plus de 12 A m-2 en présence de 50 mM de fumarate. Les expériences de stabilité ont montré la présence d’un courant biotique de 1,75 A m-2 après 24 h de réduction de 50 mM de fumarate / The aim of this PhD work was to design an artificial electroactive biofilm in order to optimize extracellular electron transfers (EET) by artificially reconstituting the biofilm in the presence of exogenous materials. A biocomposite material was proposed from the self-assembly of the bacteria Shewanella oneidensis with carbon nanotubes and cytochrome c (extract from bovine heart). The self-assembly was first studied by diffusion light scattering, scanning electron microscopy and Raman spectroscopy. These analyzes showed the importance of the cytochrome c in the assembly and organization of the biocomposite. Bacterial viability was studied and metabolic activity was characterized with the help of electrochemistry. The current at the anode was 10 and 4 times higher with the artificial biofilm (0.027 A m2) than with film composed with bacteria alone (0.003 A m2) or associated with cytochrome c (0.007 A m2). Artificial biofilm was also tested with Pseudomonas fluorescens instead of S. oneidensis, producing an oxidative current upon the addition of 1.5 mM glucose. That indicates cytochrome c has, in addition to its structuring role, an electron shuttle activity. Its redox potential, +254 mV (vs. NHE), was adapted to the oxidation of formate but was unsuitable for the reduction of fumarate. For this reason, it has been substituted by other cytochromes, c3DvH, c7Da, c553DvH, c3DdN, and c3Dg, possessing lower redox potentials, in the range of 20 mV to -400 mV. These cytochromes also varied at the level of their charge at neutral pH and allowed to validate the importance of the electrostatic forces in the assembly of the biocomposite. The optimal results obtained with c3DvH and c7Da showed the importance of the redox potential of the exogenous elements for the EET. We then replaced the cytochrome c with protamine. This non-electroactive protein allowed the assembly of the biocomposite by promoting direct electrons transfer between the bacteria and the different nanomaterials tested. The optimizations made it possible to reach cathodic currents of more than 12 A m2 in the presence of 50 mM of fumarate. The stability experiments showed the presence of a biotic current of 1.75 A m2 after 24 h of reduction of 50 mM of fumarate

Le but de ce travail est l'étude de la bioimpédancemétrie appliquée à des populations particulières de néphrologie (hémodialyse, insuffisance rénale et transplantation), afin d'évaluer l'apport de cette technique et les facteurs d'influence modifiant la mesure ou son interprétation. Nous avons pu identifier (à travers deux appareils d'impédancemétrie) plusieurs profils de patients, selon leurs « réponses » à la technique de bioimpédance, en fonction des séances d'hémodialyse, de l'âge, des comorbidités, de matériel implantable, de la fonction rénale après transplantation. Il y a une bonne validité des données physiques mesurées. Sur les valeurs calculées, il y a des valeurs aberrantes, tant sur les volumes hydriques que sur le diagnostic d'hydratation (calcul de l'excès d'eau). La principale hypothèse est l'existence d'algorithmes dans les logiciels, établis sur des populations caractéristiques, et avec de nombreux facteurs correctifs, mais qui restent inadaptés dès que le sujet mesuré s'éloigne un peu de ces patients « normés ». La présence de matériel dans le corps humain influencerait les mesures et rendrait les algorithmes inadaptés. Ce travail nous amène à conclure que quelque soit le logiciel, donc l'appareil utilisé, le patient devrait être son propre témoin de mesure, hypothèse non vérifiée dans la littérature. Enfin, le deuxième point de recherche pourrait être la notion d'une fréquence tissulaire propre à chacun, autre que la classique fréquence de 50 kHz, celle théorique à laquelle l'effet capacitif membranaire est maximal, et caractérise donc la cellule. Notre étude montre que cette fréquence est loin d'être de 50 kHz. Les études restent à faire / The goal of this work is to study bioimpedance through different and particular people in nephrology (hemodialysis, renal disease or kidney graft), to assess this electrical engineering and the factors of onfluence that can change the measures or their meaning. We succeed to identify (through two bioimpedance instrument) several profiles of patients, according to their "response and behaviour" to this bioimpedance technique, depending on hemodialysis sessions, age, morbidity, presence of electrical device or after kidney transplantation. Through our population, we find a good validity of the electrical and physical measures. But when the values body composition are calculated from the electrical data, there is often aberrant values, concerning body composition, fluid compartment or the excess water. The main hypothesis is the existence of algorithms in the devices, compiled from statistics on healthy populations, with several corrective factors, but these algorithms probably don't fit with "particular" population. This work allows us to propose that what are the devices used, the patient might be his own measure witness. There is no study in the literature. Finally, an idea could be the existence of a specific tissue frequency, specific to each one, and different from the theoretical frequency of 50 kHz. This 50 kHz frequency corresponds to the highest cell membrane capacity and so characterizes the cell. Our study shows that the frequency corresponding to this highest reactance is precisely not 50 kHz. The hypothesis is the existence of a own characteristic frequency. Sudies remain to be done