| 1. |
- Guo, Weijin, et al.
(författare)
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"Bend-and-bond" polymer microfluidic origami
- 2021
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Ingår i: 2021 34th IEEE international conference on micro electro mechanical systems (MEMS 2021). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 222-225
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Konferensbidrag (refereegranskat)abstract
- We report the fabrication of polymer microstructures with inert surface finish by folding and self-bonding. Layers of off-stoichiometric thiol-ene-epoxy (OSTE+) were fabricated using UV photocuring (1st curing step) of resin, which resulted in a malleable sheet with unreacted groups at its surface. The sheets were structured by either photomasking during the 1st curing step or by cutting postcuring using x urography. The sheets were subsequently folded into a desired shape. Last, the folded structures were thermally cured (2nd curing step), during which surfaces in contact with each other spontaneously bond, the polymer stiffens, the folding stress is released, and reactive surface groups are consumed. We used this unique bend-and-bond technique to demonstrate three sample structures: a multilayer microfluidic chip with crossing channels, a helical spring, and a functional mini windmill. We believe OSTE+ origami can find further applications in the fabrication of biochips and biosensors.
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| 2. |
- Guo, Weijin, 1989-, et al.
(författare)
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Capillary Pumping Independent Of Liquid Sample Viscosity
- 2016
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Ingår i: Langmuir. - Washington, DC 20036 : American Chemical Society (ACS). - 0743-7463 .- 1520-5827.
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Tidskriftsartikel (refereegranskat)abstract
- Capillary flow is a dominating liquid transport phenomenon on the micro- and nanoscale. As described at the beginning of the 20th century, the flow rate during imbibition of a horizontal capillary tube follows the Washburn equation, i.e. decreases over time and depends on the viscosity of the sample. This poses a problem for capillary driven systems that rely on a predictable flow rate and where the liquid viscosity is not precisely known. Here we introduce and successfully experimentally verify the first compact capillary pump design with a flow rate constant in time and independent of the liquid viscosity that can operate over an extended period of time. We also present a detailed theoretical model for gravitation independent capillary filling, which predicts the novel pump performance to within measurement error margins, and in which we, for the first time, explicitly identify gas inertia dominated flow as a fourth distinct flow regime in capillary pumping. These results are of potential interest for a multitude of applications and we expect our results to find most immediate applications within lab-on-a-chip systems and diagnostic devices.
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| 3. |
- Guo, Weijin, 1989-, et al.
(författare)
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Capillary pumping independent of the liquid surface energy and viscosity
- 2018
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Ingår i: Microsystems & Nanoengineering. - : Springer Nature. - 2055-7434. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Capillary pumping is an attractive means of liquid actuation because it is a passive mechanism, i.e., it does not rely on an external energy supply during operation. The capillary flow rate generally depends on the liquid sample viscosity and surface energy. This poses a problem for capillary-driven systems that rely on a predictable flow rate and for which the sample viscosity or surface energy are not precisely known. Here, we introduce the capillary pumping of sample liquids with a flow rate that is constant in time and independent of the sample viscosity and sample surface energy. These features are enabled by a design in which a well-characterized pump liquid is capillarily imbibed into the downstream section of the pump and thereby pulls the unknown sample liquid into the upstream pump section. The downstream pump geometry is designed to exert a Laplace pressure and fluidic resistance that are substantially larger than those exerted by the upstream pump geometry on the sample liquid. Hence, the influence of the unknown sample liquid on the flow rate is negligible. We experimentally tested pumps of the new design with a variety of sample liquids, including water, different samples of whole blood, different samples of urine, isopropanol, mineral oil, and glycerol. The capillary filling speeds of these liquids vary by more than a factor 1000 when imbibed to a standard constant cross-section glass capillary. In our new pump design, 20 filling tests involving these liquid samples with vastly different properties resulted in a constant volumetric flow rate in the range of 20.96–24.76 μL/min. We expect this novel capillary design to have immediate applications in lab-on-a-chip systems and diagnostic devices.
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| 4. |
- Guo, Weijin, 1989-, et al.
(författare)
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Capillary pumping with a constant flow rate independent of the liquid sample viscosity and surface energy
- 2017
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Ingår i: Proceeding of 2017 IEEE 30th International Conference on Micro Electro Mechanical Systems (MEMS). - : IEEE. - 9781509050789
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Konferensbidrag (refereegranskat)abstract
- We introduce and experimentally verify a capillary pump design that, for the first time, enables autonomous pumping of sample liquid with a flow rate constant in time and independent of the sample viscosity and sample surface energy. These results are of interest for applications that rely on a predictable flow rate and where the sample fluid viscosity or surface energy are not precisely known, e.g. in capillary driven diagnostic lateral flow biosensors for urine or blood sample, where large variations exist in both viscosity and surface energy between different patient samples.
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| 5. |
- Guo, Weijin, et al.
(författare)
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Formation of a thin-walled Spider Silk Tube on a Micromachined Scaffold
- 2018
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Ingår i: Proceeding of 2018 IEEE 31st International Conference on Micro Electro Mechanical Systems (MEMS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538647820 ; , s. 83-85
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Konferensbidrag (refereegranskat)abstract
- This paper reports on the first formation of a thin bio-functionalized spider silk tube, supported by an internal micromachined scaffold, in which both the inside and outside of the tube wall are freely accessible. The silk tube could potentially be used as an artificial blood vessel in an in vitro tissue scaffold, where endothelial cells and tissue cells can grow on both sides of the silk tube.
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| 6. |
- Guo, Weijin, et al.
(författare)
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Immunoassays on thiol-ene synthetic paper generate a superior fluorescence signal
- 2020
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Ingår i: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- The fluorescence-based detection of biological complexes on solid substrates is widely used in microarrays and lateral flow tests. Here, we investigate thiol-ene micropillar scaffold sheets (“synthetic paper”) as the solid substrate in such assays. Compared to state-of-the-art glass and nitrocellulose substrates, assays on synthetic paper provide a stronger fluorescence signal, similar or better reproducibility, lower limit of detection (LOD), and the possibility of working with lower immunoreagent concentrations. Using synthetic paper, we detected the antibiotic enrofloxacin in whole milk with a LOD of 1.64 nM, which is on par or better than the values obtained with other common tests, and much lower than the maximum level allowed by European Union regulations. The significance of these results lays in that they indicate that synthetically-derived microstructured substrate materials have the potential to improve the performance of diagnostic assays.
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| 7. |
- Guo, Weijin, et al.
(författare)
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Quantitative Glucose Measurement on a Synthetic Paper Test Strip
- 2021
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Ingår i: 2021 IEEE 16th international conference on nano/micro engineered and molecular systems (nems). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1310-1313
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Konferensbidrag (refereegranskat)abstract
- To measure the glucose concentration in blood is an important target for point-of-care diagnostics. We integrated a colorimetric assay on synthetic paper, a novel lateral flow test substrate, for quantitative glucose measurement. At first, we dropped a colorimetric enzyme assay in silk solution on one end of the synthetic paper test strip and dried it in a vacuum chamber for overnight. After that, we flowed glucose solution on the test strip, imaged the test strip by smartphone, and analyzed the images with ImageJ. Exponential fitting of the experimental data revealed a low limit of detection of the assay to be 0.21 mM, and the R-2 is 0.99 for the concentration (0 - 15 mM), which covers the clinically relevant blood glucose concentration (2 - 12 mM). This test strip can he further developed into a test for glucose quantification in whole blood.
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| 8. |
- Guo, Weijin, et al.
(författare)
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Synthetic microfluidic paper with superior fluorescent signal readout
- 2019
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Ingår i: Proceedings of The 23rd International Conference on Miniaturized Systems for Chemistry and Life Sciences. - 9781733419000 ; , s. 1056-1057
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Konferensbidrag (refereegranskat)abstract
- This work is the first report on the use of synthetic microfluidic paper for lateral flow immunoassays. We grafted test lines of biotin on the synthetic paper using the thiol-yne “click” reaction. We captured fluorescently labeled streptavidin in a lateral flow fashion. Our two main findings are that, compared to other polymer lateral flow substrates with similar surface area, the synthetic microfluidic paper geometry results in 1) a stronger and more stable fluorescent signal per capture area, and 2) a sensitivity ~7 times higher.
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| 9. |
- Guo, Weijin, 1989-
(författare)
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Synthetic Paper for Point-of-Care Diagnostics : Capillary control, surface modifications, and their applications
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Capillary-based platforms for diagnostics are popular for the point-of-care diagnostics market because of their low cost, easy fabrication, and easy operation. Lateral flow tests are an excellent example of capillary-based platforms for point-of-care diagnostics. However, most current lateral flow tests can only provide qualitative results or have low sensitivity. Lateral flow tests with better performance are needed. In this thesis, I tried to improve the performance of lateral flow tests from different aspects: flow rate control, surface modification, plasma separation, and immunoassay application.Variations in sample liquid properties (viscosity and surface energy) can lead to variations in the flow rate, and therefore variations in the lateral flow test results. I developed a novel capillary pump system that can provide a constant pumping flow rate independent of liquid surface energy and viscosity. This capillary pump system works well for bodily liquids, even for blood, which has low surface energy. This capillary pump system can provide a flow rate 20.96-24.76 μL/min for all the kinds of liquid tested, which is relevant for LFTs in clinical diagnostics.The substrate of lateral flow tests should be hydrophilic and must be easy to functionalize with protein for immunoassay applications. I developed surface modification protocols for the novel lateral flow test substrate - OSTE synthetic paper. I tested different hydrophilic treatments of synthetic paper, including PEGMA, HEMA, O2 plasma, and Tween 20 coating. All these treatment methods work well, and they provide slightly different hydrophilicity, and therefore different pumping velocities for liquid samples. They can be used for applications with different requirements on hydrophilicity. Moreover, I flowed blood plasma samples through the synthetic paper with different hydrophilic treatments and found that the OSTE synthetic paper surface retains low amounts of plasma protein (with a protein recovery rate close to 100%), which shows that synthetic paper is a good material for biological sample handling. I also developed and validated two protocols for grafting on synthetic paper: thiol-yne-biotin-streptavidin and thiol-maleimide-biotin-streptavidin.Plasma separation is an essential step for lateral flow tests using whole blood as the sample. Usually, commercial filtration membranes for plasma separation are added to the test strips. Such membranes, however, suffer from a protein retention. I built a plasma extractor using synthetic paper. The synthetic paper underwent hydrophilic treatment and was precoated with agglutination antibody. The agglutination antibody caused local agglutination of red blood cells, while the plasma continued pumping using capillary action, thus achieving the separation. The synthetic paper had a smaller surface area to make sure less protein is retained by the surface, resulting in a higher protein recovery rate (>82%) than commercial filtration membranes (73%).Microarray technology provides a high-throughput method to test the functionality of LFT immunoassay reagents. Nitrocellulose and glass are traditional materials for microarray platforms. I used them and synthetic paper as the substrate for a protein microarray platform, and made a systematic comparison of these three substrates with respect to the fluorescence signal. To accomplish this, I used an indirect competitive sandwich assay for the detection of the antibiotic enrofloxacin in whole milk, and fluorophore as the signal label. The experiments showed that synthetic paper could provide an overall better performance in terms of signal variance, reproducibility, limit of detection, and goodness of fit. I further investigated the influence of synthetic paper geometry design on the assay performance and chose the best design for matrix study of milk. I found the matrix effect of milk to be low, and that synthetic paper can be used for enrofloxacin detection in whole milk. The LOD of enrofloxacin detection in whole milk is 1.64 nM, which is much lower than the concentration (288.98 nM) stipulated by EU regulations.The results of the microarray platform can provide guidelines for designing lateral flow tests using synthetic paper as the substrate.These contributions can be combined or used individually to improve the performance of lateral flow tests on reproducibility and/or sensitivity. Synthetic paper has been proved to be a good substrate for LFTs by allowing easy sample handling and immunoassay coupling, and will find wider applications in the field of quantitative LFTs.
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| 10. |
- Guo, Weijin, et al.
(författare)
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Synthetic Paper Separates Plasma from Whole Blood with Low Protein Loss
- 2020
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Ingår i: Analytical Chemistry. - Washington D.C. : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 92:9, s. 6194-6199
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Tidskriftsartikel (refereegranskat)abstract
- The separation of plasma from whole blood is the first step in many diagnostic tests. Point-of-care tests often rely on integrated plasma filters, but protein retention in such filters limits their performance. Here, we investigate plasma separation on interlocked micropillar scaffolds ("synthetic paper") by the local agglutination of blood cells coupled with the capillary separation of the plasma. We separated clinically relevant volumes of plasma with high efficiency in a separation time on par with that of state of the art techniques. We investigated different covalent and non-covalent surface treatments (PEGMA, HEMA, BSA, O2 plasma) on our blood filter and their effect on protein recovery, and identified O2 plasma treatment and 7.9 μg/cm2 agglutination antibody as most suitable treatments. Using these treatments, we recovered at least 82% of the blood plasma proteins, more than with state-of-the-art filters. The simplicity of our device and the performance of our approach could enable better point-of-care tests.
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