| 1. |
- Cárdenas, Marité, et al.
(author)
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DNA compaction onto hydrophobic surfaces by different cationic surfactants
- 2005
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:14, s. 6495-6502
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Journal article (peer-reviewed)abstract
- DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.
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| 2. |
- McLoughlin, D, et al.
(author)
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Surface complexation of DNA with insoluble monolayers. Influence of divalent counterions
- 2005
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:5, s. 1900-1907
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Journal article (peer-reviewed)abstract
- DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers of zwitterionic lipids in the presence of divalent ions. Binding to dioctadecyldimethylammonium bromide (DODAB) or distearoyl-sn-glycero-3-phosphocholine (DSPC) monolayers in the presence of calcium is accompanied by monolayer expansion. For the positively charged DODAB monolayer, this causes a decrease of surface potential, while an increase is observed for the DSPC monolayers. Binding to dipalmitoyl-sn-glycero-3-phosphocholine preserves most of the liquid expanded-liquid condensed coexistence region. The liquid condensed domains adopt an elongated morphology in the presence of DNA, especially in the presence of calcium. The interaction of DNA with phospholipid monolayers is ion specific: the presence of calcium leads to a stronger interaction than magnesium and barium. These results were confirmed by bulk complexation studies.
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| 3. |
- Nylander, Stina, 1972-
(author)
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Design and Implementation of Multi-Device Services
- 2007
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Doctoral thesis (other academic/artistic)abstract
- We present a method for developing multi-device services which allows for the creation of services that are adapted to a wide range of devices. Users have a wide selection of electronic services at their disposal such as shopping, banking, gaming, and messaging. They interact with these services using the computing devices they prefer or have access to, which can vary between situations. In some cases, the services that they want to use func-tions with the device they have access to, and sometimes it does not. Thus, in order for users to experience their full benefits, electronic services will need to become more flexible. They will need to be multi-device services, i.e. be accessible from different devices. We show that multi-device services are often used in different ways on different devices due to variations in device capabilities, purpose of use, context of use, and usability. This suggests that multi-device services not only need to be accessible from more than one device, they also need to be able to present functionality and user interfaces that suit various devices and situations of use. The key problem addressed in this work is that there are too many device-service combinations for developing a service version for each device. In-stead, there is a need for new methods for developing multi-device services which allows the creation of services that are adapted to various devices and situations. The challenge of designing and implementing multi-device services has been addressed in two ways in the present work: through the study of real-life use of multi-device services and through the creation of a development method for multi-device services. Studying use of multi-device services has gener-ated knowledge about how to design such services which give users the best worth. The work with development methods has resulted in a design model building on the separation of form and content, thus making it possible to create different presentations to the same content. In concrete terms, the work has resulted in design guidelines for multi-device services and a system prototype based on the principles of separation between form and content, and presentation control.
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| 4. |
- Nylander, Sven, et al.
(author)
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Evaluation of platelet function, a method comparison
- 2006
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In: Platelets. - : Informa UK Limited. - 0953-7104 .- 1369-1635. ; 17:1, s. 49-55
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Journal article (peer-reviewed)abstract
- Platelet function can be studied using many different methods why it is of interest to understand how data from different assays relate to each other. In the present study we compare two methods suitable for screening purposes with two established although laborious methods, impedance aggregometry and platelet-rich plasma (PRP) aggregation. The alternative assays tested were: (i) exposure of active αIIbβ3, in diluted whole blood and (ii) whole blood aggregation assessed by residual platelet counting. The fibrinogen receptor activation assay was found to have the lower variability, higher sensitivity to ADP, and higher signal to noise ratio compared with residual platelet counting. The sensitivity and response profile of the fibrinogen receptor activation assay and residual platelet counting were more similar to PRP aggregation than to impedance aggregometry, whereas impedance aggregometry displayed lower sensitivity to ADP. The two alternative assays correlated well with PRP aggregation as well as with each other. The fibrinogen receptor activation assay displayed the highest potency for AR-C69931MX, possibly due to a lower protein content compared with residual platelet counting. The two studied assays compare well with the more established assays, and are thus both good alternatives for platelet function testing and evaluation of new potential platelet antagonists.
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| 5. |
- Samoshina, Y, et al.
(author)
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Adsorption and aggregation of cationic amphiphilic polyelectrolytes on silica
- 2005
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In: Langmuir. - 0743-7463 .- 1520-5827. ; 21, s. 2855-2864
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Journal article (peer-reviewed)abstract
- The adsorption of two cationic amphiphilic polyelectrolytes, which are copolymers of two charged monomers, triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride (which is the amphiphilic one) with different contents of amphiphilic groups (40% (40DT) and 80% (80DT)), onto the hydrophilic silica-aqueous solution interface has been studied by in situ null ellipsometry and tapping mode atomic force microscopy (AFM). Adsorption isotherms for both polyelectrolytes were obtained at 25° C and at different ionic strengths, and the adsorption kinetics was also investigated. At low ionic strength, thin adsorbed layers were observed for both polyelectrolytes. The adsorption increases with polymer concentration and reaches, in most cases, a plateau at a concentration below 50 ppm. For the 80DT polymer, at higher ionic strength, an association into aggregates occurs at concentrations at and above 50 ppm. The aggregates were observed directly by AFM at the surface, and by dynamic light scattering in the solution. The adsorption data for this case demonstrated multilayer formation, which correlates well with the increase in viscosity with the ionic strength observed for 80DT.
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| 6. |
- Samoshina, Yulia, et al.
(author)
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Equilibrium aspects of polycation adsorption on silica surface: How the adsorbed layer responds to changes in bulk solution
- 2005
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:13, s. 5872-5881
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Journal article (peer-reviewed)abstract
- Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M-w is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount F of CPAM increases with pH for all studied electrolyte concentrations until a plateau F is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount. The thickness of adsorbed polymer layers, obtained by ellipsometry, increases with electrolyte concentration and decreases with pH. At low c(s) and high pH the polyelectrolyte adsorbs in a flat conformation. An overcompensation of the surface charge (charge reversal) by the adsorbed polyelectrolyte is observed at high c, and low pH. To reveal the reversibility of the polyelectrolyte adsorption with respect to the adsorbed amount and layer thickness, parameters such as polyelectrolyte concentration (cp), c(s) and pH were changed during the experiment. Generally, similar adsorbed layer properties were obtained independent of whether adsorption was obtained directly to initially bare surface or by changing pH, c(s) or the concentration of polyelectrolyte solution in the presence of a preadsorbed layer, provided that the coverage of the preadsorbed layer was low. Once a steady state of the measured parameters (Gamma, d) was reached, experimental conditions were restored to the original values and corresponding changes in Gamma and adsorbed layer thickness were recorded. For initially low surface coverage it was impossible to restore the layer properties, and in this case we always ended up with higher coverage than the initial values. For initial high surface coverage it was usually possible to restore the initial layer properties. Thus, we concluded that polyelectrolyte appears only partially reversible to changes in the solution conditions due the slow rearrangement process within the adsorbed layer.
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| 7. |
- Vandoolaeghe, Pauline, et al.
(author)
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Adsorption of cubic liquid crystalline nanoparticles on model membranes
- 2008
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 4:11, s. 2267-2277
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Journal article (peer-reviewed)abstract
- The interactions of lipid based cubic liquid crystalline nanoparticles (Cubosome (R)) with surface supported model membranes constituted of dioleylphosphatidylcholine ( DOPC) have been studied in situ by use of ellipsometry, quartz crystal microbalance with dissipation monitoring and neutron reflectivity. The systems investigated were cubic phase dispersions of glycerol monooleate (GMO) stabilised by a non-ionic block copolymer, Pluronic (R) F-127. The interaction between the cubic nanoparticles and the lipid bilayer is a dynamic process where the nanoparticles initially adsorb at the bilayer surface. Interfacial lipid exchange takes place where GMO is delivered into the bilayer and DOPC is extracted into the nanoparticle (34% loss). A subsequent release of the adsorbates can be triggered when the solution concentration exceeds 0.002 mg ml(-1). The release shows that the attractive interaction between the cubic nanoparticles and lipid bilayer is unstable after sufficient exchange of material takes place.This instability is indicative of a local phase separation at the interface between the bilayer and the nanoparticles, which causes desorption of nanoparticles. Some particles remain attached to the bilayer even hours after the initial interaction. The ability to trigger the release of the nanoparticles through increasing the solution concentration offers exciting potential in the design of drug delivery aids.
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