Publication

Optical trapping and micromanipulation of biological objects in microfluidic channels

Marinela Gjoni Boillat
2007
EPFL thesis
Abstract

The main aim of this project was to develop novel concepts for miniaturization of bioanalytical techniques for investigating biomolecular interactions. We used optical tweezers to selectively address individual biological objects in microfluidic channels. A general introduction of applications of optical tweezers and microfluidics is given in chapter 1. Theoretical concepts related to optical trapping and microfluidics are reviewed in chapter 2, followed by a detailed description of the instrumentation in chapter 3. In chapter 4, ligand-receptor interactions are studied under physiological conditions: whole cells or native vesicles carrying in their membrane the protein of interest are immobilized first in the laser trap inside a microfluidic channel, then the reaction is initiated by changing the solution in the region around the trap. In chapter 5 and chapter 6 respectively, surface-modified polystyrene beads are used to study ligand-receptor interactions and DNA hybridization. The examples of these different systems studied at single cell or cell-mimicking system level demonstrate the potential to perform optical trapping in microfluidic channels and thereby constitute the basis for future applications towards parallelization and automatization of (bio)analytics. Chapter 7 and chapter 8 deal with two applications of microfluidics and optical trapping separately. Chapter 7 describes an approach for downscaling cell culturing by using microfluidic chips instead of the usual cell culturing dishes. Chapter 8 deals with an application of optical tweezers, as a tool for micromanipulation at sub-cellular level. The last chapter closes the present report by giving an overall discussion of the results and outlook for further projects.

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Related concepts (32)
Microfluidics
Microfluidics refers to a system that manipulates a small amount of fluids ((10−9 to 10−18 liters) using small channels with sizes ten to hundreds micrometres. It is a multidisciplinary field that involves molecular analysis, biodefence, molecular biology, and microelectronics. It has practical applications in the design of systems that process low volumes of fluids to achieve multiplexing, automation, and high-throughput screening.
Droplet-based microfluidics
Droplet-based microfluidics manipulate discrete volumes of fluids in immiscible phases with low Reynolds number and laminar flow regimes. Interest in droplet-based microfluidics systems has been growing substantially in past decades. Microdroplets offer the feasibility of handling miniature volumes (μl to fl) of fluids conveniently, provide better mixing, encapsulation, sorting, sensing and are suitable for high throughput experiments.
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Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner similar to tweezers. If the object is held in air or vacuum without additional support, it can be called optical levitation. The laser light provides an attractive or repulsive force (typically on the order of piconewtons), depending on the relative refractive index between particle and surrounding medium.
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