PhD Defense of MARZOUK Ibtihel

Keywords :  
Sol-gel, photolithography, channel waveguide, diffraction gratings, fluorescence, dissolved oxygen, microfluidic device

Abstract :
The thesis addresses a growing topic, optical chemical sensors, whose flagship application is the real-time monitoring of cell cultures in biomedical field. These sensors operate by quantifying physicochemical parameters, e.g. the concentration of dissolved oxygen (DO), which is an indicator of cell formation, growth and viability in an aqueous medium. Many devices are already on the market, but research remains intensive to improve their performance. This one deals in particular with the sensor miniaturization, as it allows enhanced measurement speed, easier handling and analysis of reduced liquid volumes. The sensor principle is based on variations in the fluorescence signal when a fluorophore, encapsulated in a matrix permeable to gaseous or ionic species and excited to a suitable wavelength, is contacted with an analyte, e.g. DO in an aqueous medium. This thesis aims at studying a new sensor configuration based on the sol-gel fabrication of channel waveguides doped with a fluorophore sensitive to OD. These waveguides are endowed with diffraction gratings at their input and output in order to inject and extract the excitation and emission signal, respectively. This work particularly highlights the potential of a high refractive index sol-gel TiO2 based resist, which can be imprinted through a single photolithography step (selective insolation / development) to form a given pattern. Various optimizations have been investigated in order to implement a reproducible elaboration process leading to uniform channel waveguides and diffraction gratings, while relying on opto-geometric characterizations. Fluorescence measurements were then carried out in air in order to validate the efficiency of the excitation signal injection, guided propagation of the excitation and emission signal in the waveguide core, and extraction of the emission signal toward a photo-detector. Finally, this architecture was introduced in a microfluidic system enabling to carry out fluorescence measurements in an aqueous medium at variable oxygen concentration according to an appropriate procedure. 

Jury members :

• Dr Michel LANGLET, RESEARCH DIRECTOR, CNRS Alps delegation : Supervisor
• Dr Audrey  POTDEVIN, ASSOCIATE PROFESSOR HDR, Institut de Chimie de Clermont-Ferrand : Reviewer
• Dr Sandrine PERRUCHAS,RESEARCHER -HDR, CNRS délégation Bretagne et Pays de la Loire : Reviewer
• Prof Isabelle  GAUTIER-LUNEAU, PROFESSOR of  UNIVERSITIES, Université Grenoble Alpes : Examiner
• Dr. David RIASSETTO, LMGP Grenoble-INP : Co-supervisor
• Dr Davide BUCCI, ASSOCIATE PROFESSOR HDR, IMEP-LAHC : Co-supervisor