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Development of materials, surfaces and manufacturing methods for microfluidic applications
KTH, School of Electrical Engineering (EES), Microsystem Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents technological advancements in microfluidics. The overall goals of the work are to develop new miniaturized tests for point-of-care diagnostics and robust super-lubricating surfaces for friction reduction. To achieve these goals, novel materials, surfaces and manufacturing methods in microfluidics have been developed.

Point-of-care diagnostic tests are portable miniaturized instruments that downscale and automate medical tests previously performed in the central laboratories of hospitals. The instruments are used in the doctor’s office, in the emergency room or at home as self-tests. By bringing the analysis closer to the patient, the likelihood of an accurate diagnosis, or a quick therapy adjustment is increased. Already today, there are point-of-care tests available on the market, for example blood glucose tests, rapid streptococcus tests and pregnancy tests. However, for more advanced diagnostic tests, such as DNA-tests or antibody analysis, integration of microfluidic functions for mass transport and sample preparation is required. The problem is that the polymer materials used in academic development are not always suited for prototyping microfluidic components for sensitive biosensors. Despite the enormous work that has gone into the field, very few technical solutions have been implemented commercially.

The first part of the work deals with the development of prototype point of-care tests. The research has focused on two major areas: developing new manufacturing methods to leverage the performance of existing materials and developing a novel polymer material platform, adapted for the extreme demands on surfaces and materials in miniaturized laboratories. The novel manufacturing methods allow complex 3D channel networks and the integration of materials with different surface properties. The novel material platform is based on a novel off-stoichiometry formulation of thiol-enes (OSTE) and has very attractive material and manufacturing properties from a lab-on-chip perspective, such as, chemically stable surfaces, low absorption of small molecules, facile and inexpensive manufacturing process and a biocompatible bonding method. As the OSTE-platform can mirror many of the properties of commercially used polymers, while at the same time having an inexpensive and facile manufacturing method, it has potential to bridge the gap between research and commercial production.

Friction in liquid flows is a critical limiting factor in microfluidics, where friction is the dominant force, but also in marine applications where frictional losses are responsible for a large part of the total energy consumption of sea vessels. Microstructured surfaces can drastically reduce the frictional losses by trapping a layer of air bubbles on the surface that can act as an air bearing for the liquid flow. The problem is that these trapped air bubbles collapse at the liquid pressures encountered in practical applications.

The last part of the thesis is devoted to the development of novel low fluidfriction surfaces with increased robustness but also with active control of the surface friction. The results show that the novel surfaces can resist up to three times higher liquid pressure than previous designs, while keeping the same friction reducing capacity. The novel designs represent the first step towards practical implementation of micro-structured surfaces for friction reduction.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , xiii, 87 p.
Series
Trita-EE, ISSN 1653-5146 ; 2011:058
Keyword [en]
microsystem technology, MEMS, microfluidics, polymers, off-stoichiometry thiol-ene, point-of-care, lab-on-chip
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-38605ISBN: 978-91-7501-086-1 (print)OAI: oai:DiVA.org:kth-38605DiVA: diva2:437739
Public defence
2011-09-23, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20110907

Available from: 2011-09-02 Created: 2011-08-30 Last updated: 2012-09-03Bibliographically approved
List of papers
1. A packaged optical slot-waveguide ring resonator sensor array for multiplex label-free assays in labs-on-chips
Open this publication in new window or tab >>A packaged optical slot-waveguide ring resonator sensor array for multiplex label-free assays in labs-on-chips
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2010 (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 10, no 3, 281-290 p.Article in journal (Refereed) Published
Abstract [en]

We present the design, fabrication, and characterisation of an array of optical slot-waveguide ring resonator sensors, integrated with microfluidic sample handling in a compact cartridge, for multiplexed real-time label-free biosensing. Multiplexing not only enables high throughput, but also provides reference channels for drift compensation and control experiments. Our use of alignment tolerant surface gratings to couple light into the optical chip enables quick replacement of cartridges in the read-out instrument. Furthermore, our novel use of a dual surface-energy adhesive film to bond a hard plastic shell directly to the PDMS microfluidic network allows for fast and leak-tight assembly of compact cartridges with tightly spaced fluidic interconnects. The high sensitivity of the slot-waveguide resonators, combined with on-chip referencing and physical modelling, yields a volume refractive index detection limit of 5 x 10(-6) refractive index units (RIUs) and a surface mass density detection limit of 0.9 pg mm(-2), to our knowledge the best reported values for integrated planar ring resonators.

Keyword
MICRORING RESONATOR, SILICON, INTERFACE, BIOSENSOR, SYSTEMS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12208 (URN)10.1039/b914183a (DOI)000273744700003 ()2-s2.0-75149156504 (Scopus ID)
Note

QC 20100715

Available from: 2010-03-25 Created: 2010-03-25 Last updated: 2017-12-12Bibliographically approved
2. On-chip temperature compensation in an integrated slot-waveguide ring resonator refractive index sensor array
Open this publication in new window or tab >>On-chip temperature compensation in an integrated slot-waveguide ring resonator refractive index sensor array
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2010 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 4, 3226-3237 p.Article in journal (Refereed) Published
Abstract [en]

We present an experimental study of an integrated slot-waveguide refractive index sensor array fabricated in silicon nitride on silica. We study the temperature dependence of the slot-waveguide ring resonator sensors and find that they show a low temperature dependence of -16.6 pm/K, while at the same time a large refractive index sensitivity of 240 nm per refractive index unit. Furthermore, by using on-chip temperature referencing, a differential temperature sensitivity of only 0.3 pm/K is obtained, without individual sensor calibration. This low value indicates good sensor-to-sensor repeatability, thus enabling use in highly parallel chemical assays. We demonstrate refractive index measurements during temperature drift and show a detection limit of 8.8 x 10(-6) refractive index units in a 7 K temperature operating window, without external temperature control. Finally, we suggest the possibility of athermal slot-waveguide sensor design.

Keyword
SILICON, DENSITY, DEVICES
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-12207 (URN)10.1364/OE.18.003226 (DOI)000274795700002 ()2-s2.0-77149146784 (Scopus ID)
Projects
SABIO
Note
QC 20100715Available from: 2010-03-25 Created: 2010-03-25 Last updated: 2017-12-12Bibliographically approved
3. A High-Yield Process for 3-D Large-Scale Integrated Microfluidic Networks in PDMS
Open this publication in new window or tab >>A High-Yield Process for 3-D Large-Scale Integrated Microfluidic Networks in PDMS
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2010 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 19, no 5, 1050-1057 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an uncomplicated high-yield fabrication process for creating large-scale integrated (LSI) 3-D microfluidic networks in poly(dimethylsiloxane) (PDMS). The key innovation lays in the robust definition of miniaturized out-of-plane fluidic interconnecting channels (=vias) between stacked layers of microfluidic channels in standard PDMS. Unblocked vias are essential for creating 3-D microfluidic networks. Previous methods either suffered from limited yield in achieving unblocked vias due to residual membranes obstructing the vias after polymerization, or required complicated and/or manual procedures to remove the blocking membranes. In contrast, our method prevents the formation of residual membranes by inhibiting the PDMS polymerization on top of the mold features that define the vias. In addition to providing unblocked vias, the inhibition process also leaves a partially cured, sticky flat-top surface that adheres well to other surfaces and that allows self-sealing stacking of several PDMS layers. We demonstrate the new method by manufacturing a densely perforated PDMS membrane and an LSI 3-D PDMS microfluidic channel network. We also characterize the inhibition mechanism and study the critical process parameters. We demonstrate that the method is suitable for structuring PDMS layers with a thickness down to 10 mu m.

Keyword
Inhibition, lab-on-a-chip, microfluidics, poly(dimethylsiloxane) (PDMS), 3-D structures
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-26259 (URN)10.1109/JMEMS.2010.2067203 (DOI)000283369500004 ()2-s2.0-77957573156 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme
Note
QC 20110127Available from: 2011-01-27 Created: 2010-11-21 Last updated: 2017-12-11Bibliographically approved
4. Beyond PDMS: off-stoichiometry thiol–ene (OSTE) based soft lithography for rapid prototyping of microfluidic devices
Open this publication in new window or tab >>Beyond PDMS: off-stoichiometry thiol–ene (OSTE) based soft lithography for rapid prototyping of microfluidic devices
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2011 (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 11, no 18, 3136-3147 p.Article in journal (Refereed) Published
Abstract [en]

In this article we introduce a novel polymer platform based on off-stoichiometry thiol–enes (OSTEs), aiming to bridge the gap between research prototyping and commercial production of microfluidic devices. The polymers are based on the versatile UV-curable thiol–ene chemistry but takes advantage of off-stoichiometry ratios to enable important features for a prototyping system, such as one-step surface modifications, tuneable mechanical properties and leakage free sealing through direct UV-bonding. The platform exhibits many similarities with PDMS, such as rapid prototyping and uncomplicated processing but can at the same time mirror the mechanical and chemical properties of both PDMS as well as commercial grade thermoplastics. The OSTE-prepolymer can be cast using standard SU-8 on silicon masters and a table-top UV-lamp, the surface modifications are precisely grafted using a stencil mask and the bonding requires only a single UV-exposure. To illustrate the potential of the material we demonstrate key concepts important in microfluidic chip fabrication such as patterned surface modifications for hydrophobic stops, pneumatic valves using UV-lamination of stiff and rubbery materials as well as micromachining of chip-to-world connectors in the OSTE-materials.

Place, publisher, year, edition, pages
RSC Publishing, 2011
Keyword
LoC lab-on-chip OSTE thiol-enes microfluidics
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-38607 (URN)10.1039/c1lc20388f (DOI)000294263400014 ()2-s2.0-80052226391 (Scopus ID)
Projects
Intopsens
Note

QC 20110831

Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2017-12-08Bibliographically approved
5. Biocompatible "click" wafer bonding for microfluidic devices
Open this publication in new window or tab >>Biocompatible "click" wafer bonding for microfluidic devices
2012 (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 12, no 17, 3032-3035 p.Article in journal (Refereed) Published
Abstract [en]

We introduce a novel dry wafer bonding concept designed for permanent attachment of micromolded polymer structures to surface functionalized silicon substrates. The method, designed for simultaneous fabrication of many lab-on-chip devices, utilizes a chemically reactive polymer microfluidic structure, which rapidly bonds to a functionalized substrate via "click" chemistry reactions. The microfluidic structure consists of an off-stoichiometry thiol-ene (OSTE) polymer with a very high density of surface bound thiol groups and the substrate is a silicon wafer that has been functionalized with common bio-linker molecules. We demonstrate here void free, and low temperature (<37 degrees C) bonding of a batch of OSTE microfluidic layers to a silane functionalized silicon wafer.

Place, publisher, year, edition, pages
RSC Publishing, 2012
Keyword
Adhesive, wafer bonding, heterogeneous integration, OSTE
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-38608 (URN)10.1039/c2lc21098c (DOI)000307066400008 ()2-s2.0-84864674588 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20120903. Updated from submitted to published.

Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2017-08-15Bibliographically approved
6. Sustained Superhydrophobic Friction Reduction at High Liquid Pressures and Large Flows
Open this publication in new window or tab >>Sustained Superhydrophobic Friction Reduction at High Liquid Pressures and Large Flows
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 1, 487-493 p.Article in journal (Refereed) Published
Abstract [en]

This Article introduces and experimentally explores a novel self-regulating method for reducing the friction losses in large microchannels at high liquid pressures and large liquid flows, overcoming previous limitations with regard to sustainable liquid pressure on a superhydrophobic surface. Our design of the superhydrophobic channel automatically adjusts the gas pressure in the lubricating air layer to the local liquid pressure in the channel. This is achieved by pneumatically connecting the liquid in the microchannel to the gas-pockets trapped at the channel wall through a pressure feedback channel. When liquid enters the feedback channel, it compresses the air and increases the pressure in the gas-pocket. This reduces the pressure drop over the gas liquid interface and increases the maximum sustainable liquid pressure. We define a dimensionless figure of merit for superhydropbic flows, W-F = PLD/gamma cos(theta(c)), which expresses the fluidic energy carrying capacity of a superhydrophobic microchannel. We experimentally verify that our geometry can sustain three times higher liquid pressure before collapsing, and we measured better friction-reducing properties at higher W-F values than in previous works. The design is ultimately limited in time by the gas-exchange over the gas-liquid interface at pressures exceeding the Laplace pressure. This method could be applicable for reducing near-wall laminar friction in both micro and macro scale flows.

National Category
Chemical Sciences Atom and Molecular Physics and Optics Materials Engineering
Identifiers
urn:nbn:se:kth:diva-29363 (URN)10.1021/la103624d (DOI)000285560400066 ()
Note
QC 20110204Available from: 2011-02-04 Created: 2011-02-01 Last updated: 2017-12-11Bibliographically approved
7. Continuous flow switching by pneumatic actuation of the air lubrication layer on superhydrophobic microchannel walls
Open this publication in new window or tab >>Continuous flow switching by pneumatic actuation of the air lubrication layer on superhydrophobic microchannel walls
Show others...
2008 (English)In: 21st IEEE International Conference on Micro Electro Mechanical Systems (IEEE MEMS 2008), IEEE conference proceedings, 2008, 599-602 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper introduces and experimentally verifies a method for robust, active control of friction reduction in microchannels, enabling new flow control applications and overcoming previous limitations with regard to sustainable liquid pressure. The air pockets trapped at a

superhydrophobic micrograting during liquid priming are coupled to an actively controlled pressure source, allowing the pressure difference over the air/liquid interface to be dynamically adjusted. This allows for manipulating the friction reduction properties of the surface, enabling active control of liquid mass flow through the channel. It also permits for sustainable air lubrication at theoretically unlimited liquid pressures, without loss of superhydrophobic properties. With the non-optimized grating used in the experiment, a difference in liquid mass flow of 4.8 % is obtained by alternatively collapsing and recreating the air pockets using the coupled pressure source, which is in line with a FE analysis of the same geometry. A FE analysis of a more optimized geometry predicts a mass flow change of over 30%, which would make possible new microfluidic devices based on local friction control. It is also experimentally shown that our method allows for sustainable liquid pressure 3 times higher than the Laplace pressure of a passive device.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2008
Series
PROCEEDINGS: IEEE MICRO ELECTRO MECHANICAL SYSTEMS, ISSN 1084-6999
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24758 (URN)10.1109/MEMSYS.2008.4443727 (DOI)000253356900150 ()2-s2.0-50149113512 (Scopus ID)978-1-4244-1792-6 (ISBN)
Conference
21st IEEE International Conference on Micro Electro Mechanical Systems (IEEE MEMS 2008), Tucson, AZ, USA, 13-17 Jan, 2008
Note

QC 20101011

Available from: 2010-10-11 Created: 2010-09-27 Last updated: 2015-06-04Bibliographically approved
8. Biosticker: patterned microfluidic stickers for rapid integration with microarrays
Open this publication in new window or tab >>Biosticker: patterned microfluidic stickers for rapid integration with microarrays
Show others...
2011 (English)In: The 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences (microTAS 2011), Chemical and Biological Microsystems Society , 2011, 311-313 p.Conference paper, Published paper (Refereed)
Abstract [en]

We present a one-step, reversible, and biocompatible bonding method of a stiff patterned microfluidic "Biosticker", based on off-stoichiometry thiol-ene (OSTE) polymers [1], to state-of-the-art spotted microarray surfaces. The method aims at improving and simplifying the batch back-end processing of microarrays. We illustrate its ease of use in two applications: a high sensitivity flow-through protein assay; and a DNA-hybridization test. Read-out was performed in a standard highvolume array scanner, and showed excellent spot homogeneity and intensity. The Biosticker is aimed to be a plug-in for existing microarray platforms to enable faster protein assays and DNA hybridizations through mass transport optimization.

Place, publisher, year, edition, pages
Chemical and Biological Microsystems Society, 2011
Keyword
microarrays, lab-on-chip loc, OSTE, off-stoichiometry thiol-ene, microfluidic packaging
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-38609 (URN)2-s2.0-84877953846 (Scopus ID)9781618395955 (ISBN)
Conference
The 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences (microTAS 2011)
Projects
Positive
Note

QC 20110902

Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2015-06-03Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • de-DE
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