| 1. |
- Thorslund, Sara, et al.
(author)
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A PDMS-based disposable microfluidic sensor for CD4+ lymphotic counting
- 2008
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In: Biomedical microdevices (Print). - : Springer Science and Business Media LLC. - 1387-2176 .- 1572-8781. ; 10:6, s. 851-857
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Journal article (peer-reviewed)abstract
- A refined sensor for CD4+ lymphocyte count was developed and evaluated by comparison to flow cytometry. The micropillar structured sensor surface was cast in PDMS polymer and surface modified to gain biocompatibility and CD4-cell capturing properties. The sensor works by pure capillary action and sample filling and rinsing is performed without external equipment. Whole blood samples showed acceptable agreement (79%) with flow cytometry, however when diluting the blood in PBS buffer we discovered that a larger number of cells were drawn into the sensor microchannel compared to the initial sample, explained by enhanced shear-induced cell migration. Using plasma or PBS with glycerol or albumin additives as diluting media greatly influenced this cell behavior, showing the importance of controlling the dilution media when working with devices based on capillary filling. The sensors need to be further tested with blood samples with lower CD4-counts (<500 cells/μl), which are clinically relevant.
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| 2. |
- Thorslund, Sara, et al.
(author)
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Bioactivated PDMS microchannel evaluated as sensor for human CD4+ cells : The concept of a point-of-care method for HIV monitoring
- 2007
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In: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 123:2, s. 847-855
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Journal article (peer-reviewed)abstract
- Up to today, the number of CD4(+) lymphocytes remains the most important biological marker to determine the clinical stage of an HIV-infection. Analysis by flow cytometry, the standard method used today, is unsuitable in many developing countries, because of high costs involved and practical inconveniences. We here present the concept of an inexpensive PDMS-based point-of-care device for CD4(-)count. A simple fluorescence microscope for stained leucocytes counting is the only detection equipment needed. The biosensor surface consists of an initial heparin-based coating that adds hydrophilicity and thromboresistance to the PDMS material. The specific capturing chemistry is based on an avidin/biotin-antibody surface architecture. Pure capillary forces draw whole blood, as well as rinsing buffer, into the biosensor channel, minimizing the need of external equipment. Detection of the captured cells was performed by fluorescence imaging of HOECHST (stains cell nuclei) and CD3-FITC signals. It was shown that the non-specific adsorption of CD4(-) leucocytes was minimal to none. and the detection could therefore be done by only counting the easy identifiable HOECHST+ cells. Characterization of the biosensor coating process was additionally performed with the quartz crystal microbalance-dissipation technique.
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| 3. |
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| 4. |
- Thorslund, Sara, et al.
(author)
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Functionality and stability of heparin immobilized onto poly(dimethylsiloxane)
- 2005
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In: Colloids and Surfaces B. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 45:2, s. 76-81
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Journal article (peer-reviewed)abstract
- Poly(dimethylsiloxane) (PDMS) has become an attractive material when working in the field of microfluidics, mainly because of the rapid prototyping process it involves. The increased surface volume ratio in microchannels makes the interaction between sample and material surface highly important, evident when handling complex biological samples such as plasma or blood. This study demonstrates a new grade of non-covalent heparin surface that adds efficient anticoagulant property to the PDMS material. The surface modification is a simple and fast one-step process performed at neutral pH, optimal when working with closed microsystems. The heparin formed a uniform and functional coating on hydrophobic PDMS with comparatively high level of antithrombin-binding capacity. In addition, long-term studies revelaed that the immobilized heparin was more or less stable in the microchannels over a time of three weeks. Recalcified plasma in contact with native PDMS showed complete coagulation after 1 h, while no fibrin formation was detected in plasma incubated on heparin-coated PDMS within the same time. In conclusion, we see the heparin coating developed and evaluated in this study as a tool that greatly facilitates the use of PDMS in microfluidics dealing with plasma or blood samples.
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