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Theses

Plateforme microfluidique digitale pour échantillons gazeux

Abstract : Microfluidics is the manipulation of fluids in channels of micrometer or submillimeter size. One branch of microfluidics has developed particularly in recent years, digital microfluidics, which consists in the use of simple, synchronized and programmable operations to perform more complex operations on microfluidic objects. In liquid microfluidics, the manipulated objects are usually drops formed with two immiscible fluids.Four main elementary operations are used: moving the samples, immobilizing them, mixing them and separating them. These basic operations can then be combined to perform more complex operations, such as sample analysis or processing. More original operations are also possible, such as the realization of logic gates with microfluidic cards.All the advances in digital microfluidics have been achieved by using liquid microfluidic objects dispersed in a liquid phase. Previously, work with drops has been mentioned, but work with bubbles has also been published. To our knowledge, no work has been done on the manipulation of gaseous samples in a gaseous phase.The aim of this thesis is to develop a digital microfluidic platform for the manipulation of gaseous samples dispersed in continuous gaseous phases.For this purpose, silicon microcomponents have been developed in the laboratory: the micropreconcentrators. These components include a cavity filled with an adsorbent able to trap chemical compounds when cold and to release them when hot. A heating resistor engraved on the back of the concentrator allows to control its temperature.These micro-preconcentrators can be assembled in a fluidic circuit, adding pumps to create gas flows, valves to control and direct the flows, and thermal conductivity micro-sensors developed in the laboratory.With this setup, the four basic operations of digital microfluidics could be demonstrated. A more complex operation could be performed: the measurement of the piercing volume of several linear alkanes on Tenax TA, the adsorbent used in the concentrators. The results have been published in Lab on Chip1.Other more complex operations are being studied: sample separation, which is currently difficult to perform and to model, the possibility of performing chemical reactions in the gas phase (esterification) or digital preconcentration. The latter, more advanced, is based on the use of several preconcentrators for the detection of trace volatile compounds in a sample: in a first step the compound is captured and concentrated on a first preconcentrator with a flow lower than the piercing volume, and then transferred punctually, in a second step, to a second preconcentrator placed on another fluidic path; this second preconcentrator is thus not swept by the sampling flow and the volume of gas implemented in this second step is much lower than that needed for the first one. By repeating the sampling and transfer steps, it is then possible to greatly increase the preconcentration factor of this setup without risking the breakthrough of the compound. This operation has the advantage of not having to worry about the volume of the sample: the first concentrator only needs to trap the sample, even if it is not very efficient, to be able to increase the concentration factor by repeating the operations. This allows the detection of highly volatile compounds that would not be detected in a single preconcentration step.
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Submitted on : Friday, November 26, 2021 - 11:08:11 AM
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Antoine Enel. Plateforme microfluidique digitale pour échantillons gazeux. Chimie analytique. Université Paris sciences et lettres, 2021. Français. ⟨NNT : 2021UPSLS062⟩. ⟨tel-03450832⟩

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