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A method for constructing a compact flowcell – using short taper coupling

This document details a novel approach to constructing a compact flowcell that integrates short taper coupling to improve microsphere handling and detection. The new design addresses the limitations of previous flowcell models, allowing for smaller dimensions, multiple microspheres, and easier coupling, even with high refractive index microspheres. The paper discusses the overall design goals, fabrication methods, and experimental results, highlighting the successful achievement of low-loss taper fabrication and effective microsphere coupling with high quality factors, thereby enhancing detection capabilities.

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A method for constructing a compact flowcell – using short taper coupling

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  1. A method for constructing acompact flowcell – using short taper coupling MP3L David Keng, Monica Agarwal 03/17/2008

  2. Overview • Flowcell requirements • Previous • What to change? • How to change? • New design • Fabrication • Result • Conclusion

  3. Flowcell Requirements • Contains • Microsphere • Coupling Fiber • Inlet / Outlet • Dimension • Small size overall • Small overall dimension tolerance • Previous flowcell design

  4. Flowcell – previous • To contain the coupling fiber • Flowcell has to cover the effective length of the fiber • This length is usually > 10 mm • Overall volume ~ 20 mm3 minimum • Contains only one microsphere • Difficult to contain more • Dips only and high Q not easy to track • Require exact phase matching to couple • Difficult to couple high index microspheres • What to change?

  5. What to change? Design Goal • Smaller size • Multiple microsphere • An easy way to locate high Q WGM • Possible solution for high refractive index microsphere coupling (why?) • How?

  6. How to change? • Use a fiber taper instead • Short effective length ~ 300 micron • Phase matching not as crucial • Another pick up fiber to detect peaks • Use an array of these fiber tapers • Multiple microsphere coupling • Should have at least one reference sphere

  7. Reference microsphere • Common noise rejection • Thermal drift of cell • Difficult to compensate • Thermal drift of laser • Require a high Q wavelength reference • TTL triggering delay • Can be compensated, but cannot be eliminated • Non-specific binding • Can only be detected by another microsphere • Reference microsphere • Should solve the problems above • New design

  8. Fiber taper coupling • Pump – probe configuration • Pump fiber • Excite WGM • Probe fiber • Sample WGM

  9. Flowcell – new design • Multiple pump-probe pairs • In this case, 2 • Allows two microspheres to be coupled • Within 800 microns of each other • Why this configuration?

  10. Flowcell – Planar configuration • Planar design • Low profile = small flowcell volume • Semi-automatic alignment • Microsphere coupling relatively easy

  11. Flowcell - Fabrication • Meniscus • Forms between 2 liquids • Height = Radius-1 • Creates a taper • This technique • Well established • Near field probe Silicone oil (PDMS) 48% HF acid

  12. (a) (b1) (b2) (c1) (c2) 5 min 30 min LIFT Flowcell – Fabrication detail • How to build this?

  13. Fabrication result • Smooth linear taper • Only the cladding is etched! • Propagation unchanged • Low loss <50% • Possibly due to the meniscus profile 8 micron /div 4 micron

  14. Assembling • Check fiber diameter • Fine etch to adjust diameter • UV glue under microscope • Allows time to align • Apprx. 50 micron gap between the two pairs

  15. Result • Q ~ 106 with zero background in water • Peaks can be easily tracked • Detector gain offset

  16. Conclusion • Low loss taper fabrication SOP established (15 days) • Multiple fiber SOP established (10 days, with Monica) • Assembling SOP established (3 days) • Fabrication and assembling takes ~1hr • <20 micron tolerance un-jacketed region • <1 micron tolerance on effective region diameter • Same coupling apparatus as before • Original concept 02/8/2008 (40 days) • To do: • Testing flow noise • Attempting higher refractive index microsphere coupling

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