| 1. |
- Emilsson, Gustav, 1989, et al.
(författare)
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Polymer brushes in solid-state nanopores form an impenetrable entropic barrier for proteins
- 2018
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 10:10, s. 4663-4669
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Tidskriftsartikel (refereegranskat)abstract
- Polymer brushes are widely used to prevent the adsorption of proteins, but the mechanisms by which they operate have remained heavily debated for many decades. We show conclusive evidence that a polymer brush can be a remarkably strong kinetic barrier towards proteins by using poly(ethylene glycol) grafted to the sidewalls of pores in 30 nm thin gold films. Despite consisting of about 90% water, the free coils seal apertures up to 100 nm entirely with respect to serum protein translocation, as monitored label-free through the plasmonic activity of the nanopores. The conclusions are further supported by atomic force microscopy and fluorescence microscopy. A theoretical model indicates that the brush undergoes a morphology transition to a sealing state when the ratio between the extension and the radius of curvature is approximately 0.8. The brush-sealed pores represent a new type of ultrathin filter with potential applications in bioanalytical systems.
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| 2. |
- Emilsson, Gustav, 1989, et al.
(författare)
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Strongly Stretched Protein Resistant Poly(ethylene glycol) Brushes Prepared by Grafting-To
- 2015
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 7:14, s. 7505-7515
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Tidskriftsartikel (refereegranskat)abstract
- We present a new grafting-to method for resistant non-fouling poly(ethylene glycol) brushes, which is based on grafting of polymers with reactive end groups in 0.9 M Na2SO4 at room temperature. The grafting process, the resulting brushes, and the resistance toward biomolecular adsorption are investigated by surface plasmon resonance, quartz crystal microbalance, and atomic force microscopy. We determine both grafting density and thickness independently and use narrow molecular weight distributions which result in well-defined brushes. High density (e.g., 0.4 coils per nm(2) for 10 kDa) and thick (40 nm for 20 kDa) brushes are readily achieved that suppress adsorption from complete serum (10x dilution, exposure for 50 min) by up to 99% on gold (down to 4 ng/cm(2) protein coverage). The brushes outperform oligo(ethylene glycol) monolayers prepared on the same surfaces and analyzed in the same manner. The brush heights are in agreement with calculations based on a simple model similar to the de Gennes strongly stretched brush, where the height is proportional to molecular weight. This result has so far generally been considered to be possible only for brushes prepared by grafting-from. Our results are consistent with the theory that the brushes act as kinetic barriers rather than efficient prevention of adsorption at equilibrium. We suggest that the free energy barrier for passing the brush depends on both monomer concentration and thickness. The extraordinary simplicity of the method and good inert properties of the brushes should make our results widely applicable in biointerface science.
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| 3. |
- Emilsson, Gustav, 1989, et al.
(författare)
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Surface plasmon resonance methodology for monitoring polymerization kinetics and morphology changes of brushes-evaluated with poly(N-isopropylacrylamide)
- 2017
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 396, s. 384-392
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Tidskriftsartikel (refereegranskat)abstract
- Polymerization from surfaces and the resulting “brushes” have many uses in the development of novel materials and functional interfaces. However, it is difficult to accurately monitor the polymerization rate, which limits the use of polymer brushes in applications where control of thickness is desirable. We present a new methodology based on angular surface plasmon resonance (SPR) which provides real-time measurements of the thickness evolution during atom transfer radical polymerization, using poly(N-isopropylacrylamide) as an example. Our data analysis shows that the growth is linear with a rate of ?20 nm/min in a water/methanol mixture up to ?100 nm after which chain termination gradually reduces the growth rate. Further, we introduce an improved method in SPR which makes it possible to determine changes in brush height and refractive index during switching of responsive polymers. The ratio between heights in the coil to globule transition at 32 °C in water was found to be almost 5, independent of the initial absolute height up to ?200 nm, in agreement with theory. Complementary quartz crystal microbalance and atomic force microscopy data confirm the accuracy of our results. With the methodology presented here the established SPR technique can be used for quantitative characterization of surface-initiated polymerization and responsive polymer brushes.
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| 4. |
- Malekian, Bita, 1986, et al.
(författare)
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Detecting Selective Protein Binding Inside Plasmonic Nanopores: Toward a Mimic of the Nuclear Pore Complex
- 2018
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Ingår i: Frontiers in Chemistry. - : Frontiers Media SA. - 2296-2646. ; 6:December 2018
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Tidskriftsartikel (refereegranskat)abstract
- Biosensors based on plasmonic nanostructures offer label-free and real-time monitoring of biomolecular interactions. However, so do many other surface sensitive techniques with equal or better resolution in terms of surface coverage. Yet, plasmonic nanostructures offer unique possibilities to study effects associated with nanoscale geometry. In this work we use plasmonic nanopores with double gold films and detect binding of proteins inside them. By thiol and trietoxysilane chemistry, receptors are selectively positioned on the silicon nitride interior walls. Larger (similar to 150 nm) nanopores are used detect binding of averaged sized proteins (similar to 60 kg/mol) with high signal to noise (>100). Further, we fabricate pores that approach the size of the nuclear pore complex (diameter down to 50 nm) and graft disordered phenylalanine-glycine nucleoporin domains to the walls, followed by titration of karyopherin beta 1 transport receptors. The interactions are shown to occur with similar affinity as determined by conventional surface plasmon resonance on planar surfaces. Our work illustrates another unique application of plasmonic nanostructures, namely the possibility to mimic the geometry of a biological nanomachine with integrated optical sensing capabilities.
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| 5. |
- Schoch, Rafael L., et al.
(författare)
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Protein exclusion is preserved by temperature sensitive PEG brushes
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 132, s. 362-367
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene glycol) (PEG) is widely used in biotechnology-related applications yet its temperature-dependent functionality is not well understood. Here, we use bovine serum albumin (BSA) monomers and cross-linked dimers to directly probe the height of strongly stretched PEG brushes using surface plasmon resonance (SPR) in aqueous solution. Our results show that PEG brush height follows a smooth decrease as a function of increasing temperature commencing near room temperature. Measurements obtained by BSA monomers and dimers are comparable and suggest that BSA effectively probes the leading edge of the brush with minimal penetration into its interior being supported by SPR reflectivity calculations. Further, the BSA-PEG interaction remains largely inert over the entire temperature range. Overall, PEG brushes undergo a smooth conformational transition while fully preserving its protein excluding properties far from the lower critical solution temperature.
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