Electrochemical sensing and imaging of biological samples

Alexandra Bondarenko
EPFL, 2015
EPFL thesis

Abstract

Implementation of analytical methods for biological samples (e.g. bacteria or mammalian cells) is of great importance for diagnosis and treatment of various diseases, as well as for environmental monitoring. However, analysing biological samples is a cumbersome task since it requires a high sensitivity and selectivity, a capability to sense dynamic and spatial concentration changes and time-consuming separation strategies. Although several approaches have been proposed to address all these points, there is still room for the exploration and development of new analytical platforms that contribute to the manipulation and understanding of biological systems. The aim of the present thesis is therefore to propose, characterize and implement new analytical tools that can be used for perturbing, sensing and imaging of biological samples such as adherent cancer cells. As a first approach, scanning electrochemical microscopy (SECM) was combined with cell fixations strategies in order to investigate differences between adherent melanoma cells corresponding to various cancer stages. For this purpose, alive, fixed and permeabilized cells were characterized electrochemically and additionally immunostained in order to visualize by SECM the different intracellular distribution of tyrosinase among three melanoma cancer stages. Constant height SECM is widely used for cells investigation, but the intricate cells topography can influence significantly the real probe-substrate distance and thus encumber the interpretation of the obtained experimental data. Applying soft stylus probes in a contact mode could be an alternative to alleviate such a limitation, although it can also introduce damages on the biological samples. Therefore, as the next step the applicability of the soft stylus concept towards the scanning of adherent living cells in a contact mode was investigated. As a result, modified ultra-soft probes were implemented for the successful and damage-free contact mode scanning of adherent melanoma cells. While the most of the SECM experiments with adherent cells have been devoted to the âreadingâ of a biological response, the perturbation of the cell microenvironment through spatially localized electrochemical or chemical reactions is also of high importance. Therefore, the SECM soft stylus concept was extended as a tool for locally altering the microenvironment of few adherent living cells. A re-designed electrochemical push-pull probe was employed for controlling the extracellular space of a small number of adherent cells. Besides SECM, mass-spectrometry (MS) can be also used for cancer cells characterisation. Therefore, in this thesis an intact cell matrix-assisted laser desorption/ionization MS approach was combined with various cell fixation techniques in order to obtain a simple and fast protocol for acquiring the MS fingerprint of cancer cells. As a result, the developed protocol allowed the characterization and differentiation of various melanoma cell lines in a fast and simple manner, which can be important for cancer diagnosis. Finally, the amperometric sensing approach was exported into an inkjet printed multiplexed platform for the monitoring of biological and environmental relevant samples. With this aim, a multiplexed electrochemical sensor device was fabricated by sequential inkjet printing of silver, carbon nanotubes and an insulating layer on a polyimide substrate and coupled to different magnetic beads-based immunoassay formats.

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https://infoscience.epfl.ch/record/214551?ln=en

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Alexandra Bondarenko
EPFL, 2015
EPFL thesis

Abstract

Official source

https://infoscience.epfl.ch/record/214551?ln=en

About this result

Related concepts (16)

Related concepts

Related publications (11)

Related publications

Polymer nanospray interfaces for on-line electrochemically induced modifications

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EPFL2003

Synthesis, characterization and macroscopic manipulation of carbon nanotubes

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EPFL2005

The subject of this work is the study of the electrochemical promotion of catalysis (EPOC), also called non-Faradaic electrochemical modification of catalytic activity (NEMCA). In this phenomenon, application of small currents or potentials on catalysts in contact with solid electrolytes leads to very pronounced strongly non-Faradaic and reversible changes in catalytic activity and selectivity. This work concerns the system composed of platinum film electrodes, deposited on the YSZ electrolyte (ZrO2 doped with 8% Y2O3), in contact with an oxygen containing atmosphere (the O2(g),Pt/YSZ system). The aim of this work was to focus on two points in the phenomenon of EPOC: 1) The nature of the species present on the surface of the catalyst and their impact on the catalytic activity. 2) The phenomenon of permanent promotion of catalysis (P-EPOC), for which the catalytic rate enhancement is not totally reversible, leading to a long lasting activated state. The Pt electrodes were prepared via three different methods (sputtering, thermal decomposition and screen-printing) and, as expected, the resulting microstructure, observed by scanning electron microscopy (SEM), was found to depend greatly on the preparation technique. The electrochemical response of each electrode was characterized by the technique of cyclic voltammetry. Due to the occurrence of different site-related electrochemical reactions, the voltammogram shape was highly influenced by the microstructure of the Pt/YSZ contact. Based on the preliminary studies, the cermet electrode was chosen for additional electrochemical experiments, using chronoamperometry, chronopotentiometry, cyclic voltammetry, steady state polarization and impedance spectroscopy. The results of all these techniques suggest that under anodic polarization, two parallel reactions take place. The first reaction is the oxygen evolution, giving rise to a steady state current under a constant applied potential. The other reaction is the oxygen storage (oxygen injection) in the form of Pt-O species. This second process gives rise to a time dependant current under a constant applied potential, and is therefore responsible for the pseudocapacitive behavior of the electrode. Moreover, linear sweep voltammetry measurements indicated that, by application of an anodic potential, at least three types of Pt-O species were stored, following distinct kinetics. Based on the amount of stored Pt-O and on the corresponding storage kinetics, they were attributed to three different locations on the electrode: 1) at the Pt/YSZ interface, 2) diffusing from the tpb toward the Pt/gas interface, 3) diffusing from the Pt/YSZ interface toward the bulk of the platinum electrode. It has been shown that the Pt film exhibited various activity states toward the catalytic oxidation of ethylene, depending on the oxygen species present at its surface. As evidenced by XPS measurements and in agreement with the thermodynamic data for the given system, the inactive (deactivated) state has been attributed to the formation of surface platinum oxide at T > 550°C. Decreasing the reaction temperature to 525°C caused the slow spontaneous reactivation of the catalyst and several days were necessary to reach the active state, where most of the catalyst was present in its metallic state. The catalyst activity recovery could be accelerated by the application of anodic potential pulses. In agreement with the mechanism of EPOC, this was explained by the oxide destabilizing effect of the anodically produced Oδ- species. Anodic polarization also caused reversible electrochemical promotion of catalysis at unusual high temperature (600°C). In addition, very intriguing catalytic relaxation transients were observed after prolonged anodic polarization times. Indeed, it was found that enhanced catalytic activity could be maintained for up to 10 hours after current interruption. Combination of these latter results, the related literature, the state of the art model of EPOC, and the results obtained by electrochemical techniques led to the proposition of an original model based on the processes of Pt-O storage/release at various locations of the O2(g),Pt/YSZ system. According to this model, anodic polarization produces Oδ- back-spillover species, promoting the catalytic activity, in agreement with the mechanism of EPOC. In parallel, hidden oxygen species are stored at the Pt/YSZ interface and diffuse toward the Pt phase. When the polarization is switched off, these hidden oxygen species diffuse to the gas-exposed surface and cause non-Faradaic promotion, as back-spillover Oδ- do. The large amount of stored charge and its slow diffusion controlled emergence causes the rate enhancement to last for hours.

EPFL2007