Micro-optics for multiple laser trapping in microfluidics
Optical trapping allows manipulating very small objects – varying from Angstöms to micron size particles – without physical contact by taking advantage of laser light. This technique, relying on light momentum transfer, allows manipulating biological matter (such as cells, organelles, vesicles or chemically functionalized artificial particles, etc.) and offers promising potentialities for research in biotechnology and biochemistry. Individually confining a large number of microscopic objects opens new ways for the downscaling of analysis tools for drug screening, particles sorting and the assessment of statistical data. In particular, the combination of optical trapping with microfluidics greatly enlarges the possibilities offered by both techniques. This PhD work takes place in a research aiming at developing novel bio-analytical instrumentation relying on large arrays of optical traps compatible with microfluidic systems. The dissertation focuses on the use of micro-optics for generating extended matrices of three-dimensional optical traps capable of capturing a large number of particles within microfluidic environments. The stability of optical traps is first studied with special emphasis on the conditions present in microfluidic flows, both from a theoretical and an experimental point of view, and trapping forces achievable on biological cells are investigated. A multiple optical trapping system relying on microlens arrays, adapted to work on commercial microscopes, is shown to be capable of generating arrays of more than 500 three-dimensional traps. Simultaneously trapping in multiple planes is also evidenced using matrices of microlenses, thanks to a self-imaging effect of the array of traps. Furthermore, possibilities offered by multiple optical trapping within microfluidic environments are explored. Polystyrene spheres as well as biological particles, such as native vesicles, can be trapped in arrays, manipulated inside microfluidic devices and analyzed in parallel through fluorescence microscopy while extremely small quantities of chemical reagents are flown past the array. Finally, for the sake of system miniaturization and further extension of the number of traps, multiple three-dimensional optical trapping based on arrays of miniaturized high numerical aperture parabolic mirrors is proposed, allowing the optics necessary for optical trapping, fluorescence excitation and collection to be integrated at the level of a microfluidic chip. Such miniaturized mirror matrices did not even exist before this thesis; their fabrication and characterization are detailed in this dissertation.
Keywords: Optical force ; Optical trapping / laser trapping ; Optical tweezers ; Three-dimensional (3D) traps ; Multiple optical traps / optical tweezers arrays ; Multi-level trap arrays ; Trapping efficiency ; Escape force ; Microlens arrays ; Talbot/Lohmann effect ; Micromirror arrays ; High numerical aperture (high-NA) ; Integrated optical trap ; Achromatic ; Microfluidics ; [micro]-TAS (micro-Total Analysis System) ; Lab-on-a-chip ; PDMS chip (Polydimethylsiloxane) ; Mammalian cells ; Native vesicles ; Fluorescence labeling ; Optical detection ; Bio-chemical reactions ; Force optique ; Piégeage optique / Piégeage laser ; Pincettes optiques ; Piège tridimensionnel (3D) ; Pièges optiques multiples / réseaux de pincettes optiques ; Pièges sur niveaux multiples ; Efficacité de piégeage ; Force d'échappement ; Réseaux de microlentilles ; Effet Talbot/Lohmann ; Haute ouverture numérique ; Réseaux de micromirroirs ; Piège optique intégré ; Achromatique ; Microfluidique ; [micro]-TAS (micro-Total Analysis System) ; Laboratoire sur puce ; Puce en PDMS (Polydimethylsiloxane) ; Cellules mammifères ; Vésicules natives ; Marquage par fluorescence ; Détection optique ; Réactions bio-chimiquesThèse École polytechnique fédérale de Lausanne EPFL, n° 4117 (2008)
Programme doctoral Photonique
Faculté des sciences et techniques de l'ingénieur
Institut de microtechnique
Laboratoire d'optique appliquée Prof. Salathé
Record created on 2008-05-15, modified on 2016-08-08