| 1. |
|
|
| 2. |
|
|
| 3. |
- Agthe, Michael, 1983-
(författare)
-
Crystallization on the Mesoscale : Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembly of nanoparticles is a promising route to form complex, nanostructured materials with functional properties. Nanoparticle assemblies characterized by a crystallographic alignment of the nanoparticles on the atomic scale, i.e. mesocrystals, are commonly found in nature with outstanding functional and mechanical properties. This thesis aims to investigate and understand the formation mechanisms of mesocrystals formed by self-assembling iron oxide nanocubes.We have used the thermal decomposition method to synthesize monodisperse, oleate-capped iron oxide nanocubes with average edge lengths between 7 nm and 12 nm and studied the evaporation-induced self-assembly in dilute toluene-based nanocube dispersions. The influence of packing constraints on the alignment of the nanocubes in nanofluidic containers has been investigated with small and wide angle X-ray scattering (SAXS and WAXS, respectively). We found that the nanocubes preferentially orient one of their {100} faces with the confining channel wall and display mesocrystalline alignment irrespective of the channel widths. We manipulated the solvent evaporation rate of drop-cast dispersions on fluorosilane-functionalized silica substrates in a custom-designed cell. The growth stages of the assembly process were investigated using light microscopy and quartz crystal microbalance with dissipation monitoring (QCM-D). We found that particle transport phenomena, e.g. the coffee ring effect and Marangoni flow, result in complex-shaped arrays near the three-phase contact line of a drying colloidal drop when the nitrogen flow rate is high. Diffusion-driven nanoparticle assembly into large mesocrystals with a well-defined morphology dominates at much lower nitrogen flow rates. Analysis of the time-resolved video microscopy data was used to quantify the mesocrystal growth and establish a particle diffusion-based, three-dimensional growth model. The dissipation obtained from the QCM-D signal reached its maximum value when the microscopy-observed lateral growth of the mesocrystals ceased, which we address to the fluid-like behavior of the mesocrystals and their weak binding to the substrate. Analysis of electron microscopy images and diffraction patterns showed that the formed arrays display significant nanoparticle ordering, regardless of the distinctive formation process. We followed the two-stage formation mechanism of mesocrystals in levitating colloidal drops with real-time SAXS. Modelling of the SAXS data with the square-well potential together with calculations of van der Waals interactions suggests that the nanocubes initially form disordered clusters, which quickly transform into an ordered phase.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Ainalem, Marie-Louise, et al.
(författare)
-
DNA Binding to Zwitterionic Model Membranes
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:7, s. 4965-4976
-
Tidskriftsartikel (refereegranskat)abstract
- This study shows that DNA (linearized plasmid, 4331 base pairs and salmon sperm, 2000 base pairs, respectively) adsorbs to model membranes of zwitterionic liquid crystalline phospholipid bilayers in solutions containing divalent Ca2+ rations, and also in solutions containing monovalent Na+. The interaction between DNA and surface-supported model membranes was followed in situ using null ellipsometry, quartz crystal microbalance with dissipation, as well as neutron reflectometry. In the presence of Na+ (in the absence Of multivalent ions), DNA adopts an extended coil conformation upon adsorption. The solvent content in the adsorbed layer is high, and DNA is positioned on top of the membrane. In the presence of divalent Ca2+. the driving force for the adsorption of DNA is electrostatic, and the adsorbed DNA film is not as dilute its in a solution containing Na+. Cryo-TEM and SANS were further used to investigate the interaction in bulk solution using vesicles as model membrane systems. DNA adsorption could not be identified in the presence of Na+ using SANS, but cryo-TEM indicates the presence of DNA between neighboring unilamellar vesicles. In the presence of Ca2+. DNA induces the formation of multilamellar vesicles in which DNA intercalates the lamellae. Possible electrostatic and hydrophobic mechanisms for the adsorption of DNA in solutions containing monovalent salt are discussed and compared to the observations in divalent salt.
|
|
| 7. |
- Ainalem, Marie-Louise, et al.
(författare)
-
DNA compaction induced by a cationic polymer or surfactant impact gene expression and DNA degradation.
- 2014
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in achieving gene regulation in biotechnological and biomedical applications by using synthetic DNA-binding agents. Most studies have so far focused on synthetic sequence-specific DNA-binding agents. Such approaches are relatively complicated and cost intensive and their level of sophistication is not always required, in particular for biotechnological application. Our study is inspired by in vivo data that suggest that DNA compaction might contribute to gene regulation. This study exploits the potential of using synthetic DNA compacting agents that are not sequence-specific to achieve gene regulation for in vitro systems. The semi-synthetic in vitro system we use include common cationic DNA-compacting agents, poly(amido amine) (PAMAM) dendrimers and the surfactant hexadecyltrimethylammonium bromide (CTAB), which we apply to linearized plasmid DNA encoding for the luciferase reporter gene. We show that complexing the DNA with either of the cationic agents leads to gene expression inhibition in a manner that depends on the extent of compaction. This is demonstrated by using a coupled in vitro transcription-translation system. We show that compaction can also protect DNA against degradation in a dose-dependent manner. Furthermore, our study shows that these effects are reversible and DNA can be released from the complexes. Release of DNA leads to restoration of gene expression and makes the DNA susceptible to degradation by Dnase. A highly charged polyelectrolyte, heparin, is needed to release DNA from dendrimers, while DNA complexed with CTAB dissociates with the non-ionic surfactant C12E5. Our results demonstrate the relation between DNA compaction by non-specific DNA-binding agents and gene expression and gene regulation can be achieved in vitro systems in a reliable dose-dependent and reversible manner.
|
|
| 8. |
- Ainalem, Marie-Louise, et al.
(författare)
-
DNA condensation using cationic dendrimers-morphology and supramolecular structure of formed aggregates
- 2011
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:10, s. 4577-4594
-
Forskningsöversikt (refereegranskat)abstract
- The control of DNA condensation, i.e. packaging or compaction, is essential for the living cell, but also important in many applications. One example is gene therapy that often utilises vehicles with the ability to condense DNA and thereby protect DNA against degradation, transport DNA across membranes (which act as barriers towards gene delivery), and regulate gene expression. This review discusses the ability of poly(amido amine) dendrimers to condense DNA molecules via attractive electrostatic interactions, which in turn leads to self-assembled structures with a rich variety of morphologies. The process of condensation is cooperative and kinetically controlled, and the structure of the aggregates strongly depends on the size and charge of the dendrimer, and the salt concentration of the aqueous solution. While globular aggregates are formed by large dendrimers, rods and toroids are formed by smaller sized dendrimers with lower total charge per molecule. The globular aggregates appear to be disordered, but the smaller dendrimers give rise to high-ordered packing of the DNA in ordered arrays according to a square or hexagonal unit cell. The high-ordered packing also indicates that the dendrimers deform while inducing the DNA to condense.
|
|
| 9. |
- Ainalem, Marie-Louise, et al.
(författare)
-
Dynamic light scattering and fluorescence study of the interaction between double-stranded DNA and poly(amido amine) dendrimers
- 2007
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 8:5, s. 1557-1563
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction between a cationic poly(amido amine) (PAMAM) dendrimer of generation 4 and double-stranded salmon sperm DNA in 10 mM NaBr solution has been investigated using dynamic light scattering (DLS) and steady-state fluorescence spectroscopy. The structural parameters of the formed aggregates as well as the complex formation process were studied in dilute solutions. When DNA is mixed with PAMAM dendrimers, it undergoes a transition from a semiflexible coil to a more compact conformation due to the electrostatic interaction present between the cationic dendrimer and the anionic polyelectrolyte. The DLS results reveal that one salmon sperm DNA molecule forms a discrete aggregate in dilute solution with several PAMAM dendrimers with a mean apparent hydrodynamic radius of 50 nm. These discrete complexes coexist with free DNA at low molar ratios of dendrimer to DNA, which shows that cooperativity is present in the complex formation. The formation of the complexes was confirmed by agarose gel electrophoresis measurements. DNA in the complexes was also found to be significantly more protected against DNase catalyzed digestion compared to free DNA. The number of dendrimers per DNA chain in the complexes was found to be approximately 35 as determined by steady-state fluorescence spectroscopy.
|
|
| 10. |
- Ainalem, Marie-Louise, et al.
(författare)
-
Interactions between DNA and Poly(amido amine) Dendrimers on Silica Surfaces.
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:11, s. 8625-8635
-
Tidskriftsartikel (refereegranskat)abstract
- This study increases the understanding at a molecular level of the interactions between DNA and poly(amido amine) (PAMAM) dendrimers on solid surfaces, which is a subject of potential interest in applications such as gene therapy. We have used in situ null ellipsometry and neutron reflectometry to study the structure of multilayer arrangements formed by PAMAM dendrimers of generation 2 (G2), 4 (G4), and 6 (G6) and DNA on silica surfaces. Specifically, we adsorbed cationic dendrimer layers, then we condensed DNA to form dendrimer-DNA bilayers, and last we exposed further dendrimer molecules to the interface to encapsulate DNA in dendrimer-DNA-dendrimer trilayers. The dendrimer monolayers formed initially result in the deformation of the cationic adsorbates as a result of their strong electrostatic attraction to the hydrophilic silica surface. The highest surface excess and most pronounced deformation occurs for the G6 molecules due to their relatively large size and high surface charge density. G6-functionalized surfaces give rise to the highest surface excess of DNA during the bilayer formation process. This result is explained in terms of the high number of charged binding sites in the G6 monolayer and the low electrostatic repulsion between DNA and exposed patches of silica surface due to the relatively thick G6 monolayer. The binding strengths of the silica-dendrimer and dendrimer-DNA interactions are demonstrated by the high stability of the interfacial bilayers during rinsing. For the formation of trilayers of dendrimers, DNA, and dendrimers, G2 adsorbs as a smooth layer while G4 and G6 induce the formation of less well-defined structures due to more complex DNA layer morphologies.
|
|
