Development of a microfluidic chip for on-chip optical trapping

  • Lu Wei-Chen ((PhD) Student)
  • Heidi Ottevaere (Promotor)
  • Diane De Coster (Advisor)

Student thesis: Master's Thesis


In the past decades, miniaturization has been the driving force for the development of technology. For the medical or biological research, traditionally they have to perform with bulky instruments and have to wait a long time to analyze the results. The research on lab-on-chip devices may lead to portable medical inspection devices. A lab-on-chip device is a versatile chip that integrates different kinds of functionalities into a small area ranging from millimeters to a few centimeters in size. The development of a lab-on-chip device can not only shrinks the experiment area to a small size but also enable a fast and reliable analysis. Recently, the research on single cells analysis is thriving. For this purpose, it is important to distinguish and to sort the cells based on their physical or chemical features. We want to develop a setup that is operating in a miniaturized area and that is able to hold a sample for a certain time so that we can gather its information. The technique of counter propagating dual fiber optical trap is appropriate to our demands, because the divergency of the optical fibers makes them possible to hold a larger sample in an optical trap. Besides, the optical fibers are flexible so that they can be easily integrated.
To quantify the optical trapping performance on a chip, we have to establish a model to calculate the forces exerted by a light beam when it interacts with matter. The model is based on aray tracing approach with the use of a non-sequential ray tracing software. The non-sequential ray tracing method allows for the considerations of any order of the interactions due to the "child rays" caused by reflection, refraction, etc at the interface between the light propagating medium and the trapped object. The model provides a powerful tool that can be used to design and optimize a microfluidic chip. The optical trapping will be operated in a microfluidic environment. Therefore, the trapping forces in the direction of the flow should be higher to resist the forces induced by the flow.
The basic design of the fiber trapping on chip can be further improved by implementing microlenses in the chip. The design of the microfluidic chip is limited by the boundary conditions of the fabrication technique. It limits the minimum diameter of the microfluidic channel and the distance between the fiber facet and the trapped position. By considering the limitations and with the aid of the ray tracing model, the radius of curvature and the height of the lenses can be optimized towards the maximum transverse trapping force. The improvement results from the use of the microlenses can be shown by comparing the modeling results of the two optical trapping schemes. In order to show the validity of the ray tracing model, the proof of concept optical setup is under construction. The motions of the trapped object in its equilibrium position should be recorded and analyzed for the quantification of the trapping forces exerted by the laser beam. The novelty of our design, to our knowledge, lies in the use of the integrated microlenses to enhance the performance of an dual fiber optical trap in a microfluidic chip.
Date of Award2013
Original languageEnglish
SupervisorHeidi Ottevaere (Promotor) & Diane De Coster (Advisor)


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