Integrated microlenses and multimode interference devices for microflow cytometers

Abstract

The convergence of microfabrication technologies, novel materials systems, and techniques for chemical and biochemical analysis is enabling the realisation of lab-on-a-chip technology. Products incorporating such technologies are expected to find widespread use, for example in personal medicine, food safety, water management and security. This research is driven by the demand for fast, low-cost, small, and automated chemical analysis using minimal sample and reagent volumes, in a multiplicity of applications including interrogation of individual particles such as biological cells or molecules by µflow cytometry.

Several promising optical detection methods are still in their infancy in terms of integration on to a single chip and improvements can be made to existing integrated methods. Manipulation of a free optical beam in microfluidic channels is identified as a major need to be able to realise more complex µflow cytometry detection systems. To achieve this, the integrated optics requires substantial advances. The approach in this thesis was to produce a microfluidic device with improved integrated optics, primarily for fluorescence and scattering particle detection, which can provide a platform from which to build more complex fully automated optical detection devices not yet realised. To manipulate the free beam, optical components such as waveguide lenses, both refractive and diffractive, were analytically designed and numerically simulated. An alternative device, the multimode interference device (MMI), which makes use of the self-imaging phenomenon in multimode waveguides, was also studied due to its less stringent fabrication tolerances. Optical components including channel waveguides, to route light on chip, were realised and integrated with microfluidic channels with a fabrication comprising a two-mask process developed in silica-based glass to integrate both optics and microfluidics on to a single chip. Spotsizes as low as 5.6 µm for paraxial kinoform lenses and 2.6 µm for MMIs have been measured at foci as far as 29.2 µm and 56.0 µm in a microfluidic channel. These devices pave the way to the full integration of more robust and complex microfluidic µflow cytometers.

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Identifiers

ORCID for James S. Wilkinson: orcid.org/0000-0003-4712-1697

ORCID for David P. Shepherd: orcid.org/0000-0002-4561-8184

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