Packaging of Microfluidicsystem: A microfluidic motherboard integrating fluidic and optical interconnections

Gerardo Perozziello

    Research output: Book/ReportPh.D. thesisResearch

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    The field related to the development of microfluidic systems performing bio-chemical analysis is continuously growing. Careful packaging of microsystems is vital to ensure efficient work of the device, especially at the interface between the system and the environment, where fluidic electrical and optical interconnections must be provided in a reliable manner, ease of use and low cost. The objective of this project was to investigate, design and modeling new packaging solutions to interface the microfluidic systems with the outer world and finally to design, fabricate and test a fluidic motherboard for microfluidic devices. This project can be divided in three parts:
    • Specifying the definition of packaging: what characterizes it, the weak points and difficulties and all the parameters involved and important to fulfill a successful protection and interface of a system.
    • Developing models regarding the critical parameters in packaging for ease the
    design and dimensioning of fluidic interconnection and optical external couplers and experiments have been performed to validate those.
    • Design, fabricate and testing a new polymer-based microfluidic motherboard that integrates polymer-based waveguides, external optical connector plugs and fluidic networks providing an interface between microfluidic systems and the outer world.
    The motherboard, on one hand, facilitates interconnections of several microfluidic systems for multiplexed and simultaneous analysis. On the other hand, it offers a modular network for microfluidic chips, allowing complex microfluidic processes, where each microchip has a particular function. The motherboard shows a robust design allowing an easy interconnection of several microsystems alleviating critical issues as optic alignment and fluidic interfacing. A novel procedure for integrating polymer waveguides into the motherboard has been developed. It consists of spinning a thin layer of doped polymer (doped PMMA n=1.499) onto a polymer substrate with a lower refractive index (native PMMA n=1.485). The refractive index of doped PMMA was increased to by ‘doping’ the PMMA with styrene-acrylonitrile copolymer. This gave waveguiding properties to one side of the polymer substrate which is then machined by using micromilling technology, in order to fabricate the motherboard.

    The motherboard includes:
    • Fluidic network to drive liquids from outside into the chips;
    • Pockets to house polymer microfluidicsystems;
    • Waveguides to guide light inside the chips;
    • PDMS sockets to establish high density microfluidic interconnections between the motherboard and external tubes.
    • PDMS optical connector plugs for interconnecting the polymer waveguides to the light source and to the detection system, which integrates spherical lenses aligned to several optical fibers to the other side have been fabricated. The optical connector plugs allow focusing of the light from an optical fiber to a waveguide and vice versa.

    Testing polymer-based microfluidic systems have been developed to demonstrate the performance of the motherboard. The chips contain:
    • Fluidic network;
    • waveguides;
    • integrated fluidic interconnections consisting of custom made o-rings allowing
    alignment to the connection pins of the motherboard.

    The single chips were attached to the motherboard by just pressing them onto the alignment pins. A sealed fluidic connection between chip and motherboard is ensured by the deliberate mismatch in diameter between the o-rings of the chip and the pins of the motherboard. Experiments have shown constant propagation losses around 1 dB/cm between 400 nm and 850 nm for the waveguides. Regarding the optical connector plugs, the measurements of the propagation of the light show a maximum light intensity for the plugs, which is ~50% higher than for the cleaved fiber itself and more focused with respect to lateral distribution. Induced misalignments showed less measured insertion losses for the optical plugs than a coupled cleaved fiber. Finally, the fluidic interconnections were tested reaching 3.5 bars without detection any leakage. Coupling efficiency was tested on the motherboard with the chip mounted onto it, sending a light signal having a power of 300 μW and a power of 4 μW has been detected in output.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark
    Number of pages127
    Publication statusPublished - May 2006


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