Sol-gel materials for optofluidics - process and applications

Publication: ResearchPh.D. thesis – Annual report year: 2012

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This Ph.D. thesis is concerned with the use of sol-gel materials in optofluidic applications
and the physics of DNA molecules in nanoconfinement.
The bottom-up formation of solid material, which is provided by the sol-gel process,
enables control of the chemical composition and porosity of the material. At early stages
of gelation, thin gel coatings can be structured by nanoimprint lithography, and purely
inorganic silica materials can be obtained by subsequent thermal annealing. The sol-gel
process thus constitutes a unique method for nanofabrication of silica materials of special
properties.
In this work, sol-gel silica is introduced as a new material class for the fabrication of
lab-on-a-chip devices for DNA analysis. An imprint process with a rigid, non-permeable
stamp was developed, which enabled fabrication of micro- and nanofluidic silica channels
in a single process step without use of any high-vacuum techniques. Sealing of the channels
was performed by fusion bonding of a glass cover slip to the imprinted surface, and the
applicability of the device was demonstrated by sizing experiments on DNA molecules
confined in the imprinted nanochannels.
In addition, in a fused silica device, the dynamics of linear and circular DNA molecules
was studied under pressure driven flow in a slit channel with arrays of transverse nanogrooves.
In the nanogroove geometry, transport occurs through two states of propagation: a slow,
stepwise groove-to-groove translation called the ’sidewinder’ and a fast, continuous tumbling
across the grooves called the ’tumbleweed’. Dynamical transitions between the two
states cause DNA molecules to exhibit both size- and topology-dependent velocities that
may be utilized for separation.
By templating the porosity of sol-gel silica with sub-wavelength latex particles, tuning
of the effective refractive index of the material was enabled. Using nanoimprint lithography,
a diffraction grating with refractive index of 1.33 was fabricated. This low-index
grating was used to demonstrate reconfigurability of an optically functional surface topography
by electrophoretic actuation of charged latex nanoparticles. Preliminary results
showed 22 dB modulation of the intensity of the first diffraction order.
Sol-gel material was also used as a permeable solid matrix for immobilization of
analyte-sensitive dye molecules, thus constituting a sensor material for use in reagentbased
optical sensing systems. Using the principle of hemiwicking, a method that enables
deposition of the liquid sensor material in a homogeneous layer on a well-defined region of a
surface was developed. The method simplifies the fabrication of optical sensors integrated
in disposable lab ware.
Original languageEnglish
Publication date31 Oct 2011
Number of pages125
StatePublished

Bibliographical note

PhD-thesis related to the PhD-project: "Nanoimprint litografi for optofluidik"
Author: Morten Bo Lindholm Mikkelsen
Department: DTU Nanotech
Supervisor: Anders Kristensen

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