| 1. |
- 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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| 2. |
- Ferrand-Drake Del Castillo, Gustav, 1990, et al.
(författare)
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Generic high-capacity protein capture and release by pH control
- 2020
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 56:44, s. 5889-5892
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Tidskriftsartikel (refereegranskat)abstract
- Techniques for immobilization and release of proteins are of general interest but challenging to develop. Here we show a new method for high-capacity (several µg cm-2) immobilization of proteins in polyelectrolyte brushes by multivalent hydrogen bonds. Upon increasing pH, the proteins are fully released with preserved structure and activity.
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| 3. |
- Ferrand-Drake Del Castillo, Gustav, 1990, et al.
(författare)
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Quantitative Analysis of Thickness and pH Actuation of Weak Polyelectrolyte Brushes
- 2018
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:48, s. 27516-27527
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Tidskriftsartikel (refereegranskat)abstract
- Polymer brushes are widely used as surface coatings for various inert, functional, or responsive interfaces. If the polymer can alter its protonation state (a polyelectrolyte (PE)), the brush can switch between a collapsed and swollen state with pH, which enables applications such as nanoscale actuators. However, changes in brush height as the polymer alters its charge state are not straightforward to measure accurately. Here, we show how surface plasmon resonance can be used to determine the thickness of PE brushes both in their charged and neutral states. We use different methods to measure the heights of brushes consisting of poly(acrylic acid) and the polybasic poly(2-(diethylamino)ethyl methacrylate), both prepared by atom transfer radical polymerization. We find polymers in solution that can act as refractive index probes, which do not interact with the grafted polyelectrolytes, thus providing an "exclusion height" of the brush. Importantly, the angular reflection spectrum can be used to directly identify if a probe is indeed noninteracting. Furthermore, using different noninteracting probes results in small but significant changes (∼10%) in the exclusion height as long as the probe is reasonably large (approximately >2 kg/mol). These differences cannot be attributed to probe charge. Data from multiple brushes show that the relative height increase (at physiological ionic strength), i.e., the "collapse ratio" upon charging due to pH alterations, increases with the absolute brush height. In addition, we show that the plasmonic response to the pH switching of the polyelectrolyte brush is opposite to the response of hydrophilic polymer brushes collapsing at the lower critical solution temperature. This phenomenon is explained by an increase in refractometric constant upon charging. Our study shows that surface plasmon resonance is an excellent tool for characterizing polyelectrolyte brushes and provides useful insights into pH actuation not easily obtained by other methods.
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| 4. |
- Andersson, John, 1993, et al.
(författare)
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Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation
- 2021
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 37:16, s. 4943-4952
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Tidskriftsartikel (refereegranskat)abstract
- Polymer brushes are widely used to alter the properties of interfaces. In particular, poly(ethylene glycol) (PEG) and similar polymers can make surfaces inert toward biomolecular adsorption. Neutral hydrophilic brushes are normally considered to have static properties at a given temperature. As an example, PEG is not responsive to pH or ionic strength. Here we show that, by simply introducing a polymeric acid such as poly(methacrylic acid) (PMAA), the highly hydrated brush barrier can change its properties entirely. This is caused by multivalent hydrogen bonds in an extremely pH-sensitive process. Remarkably, it is sufficient to reduce the pH to 5 for complexation to occur at the interface, which is two units higher than in the corresponding bulk systems. Below this critical pH, PMAA starts to bind to PEG in large amounts (comparable to the PEG amount), causing the brush to gradually compact and dehydrate. The brush also undergoes major rheology changes, from viscoelastic to rigid. Furthermore, the protein repelling ability of PEG is lost after reaching a threshold in the amount of PMAA bound. The changes in brush properties are tunable and become more pronounced when more PMAA is bound. The initial brush state is fully recovered when releasing PMAA by returning to physiological pH. Our findings are relevant for many applications involving functional interfaces, such as capture-release of biomolecules.
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| 5. |
- Andersson, John, 1993, et al.
(författare)
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Surface plasmon resonance sensing with thin films of palladium and platinum - quantitative and real-time analysis
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 24:7, s. 4588-4594
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Tidskriftsartikel (refereegranskat)abstract
- Surface plasmon resonance (SPR) is a highly useful technique in biology and is gradually becoming useful also for materials science. However, measurements to date have been performed almost exclusively on gold, which limits the possibility to probe chemical modifications of other metals. In this work we show that 20 nm Pd and Pt films work "fairly well" for quantitative SPR sensing of organic films despite the high light absorption. In the interval between total reflection and the SPR angle, high intensity changes occur when a film is formed on the surface. Fresnel models accurately describe the full angular spectra and our data analysis provides good resolution of surface coverage in air (a few ng cm(-2)). Overall, the Pd sensors behave quite similarly to 50 nm gold in terms of sensitivity and field extension, although the noise level in real-time measurements is similar to 5 times higher. The Pt sensors exhibit a longer extension of the evanescent field and similar to 10 times higher noise compared to gold. Yet, formation of organic layers a few nm in thickness can still be monitored in real-time. As a model system, we use thiolated poly(ethylene glycol) to make Pd and Pt protein repelling. Our findings show how SPR can be used for studying chemical modifications of two metals that are important in several contexts, for instance within heterogeneous catalysis. We emphasize the advantages of simple sample preparation and accurate quantitative analysis in the planar geometry by Fresnel models.
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| 6. |
- Ferrand-Drake Del Castillo, Gustav, 1990, et al.
(författare)
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Electrically Switchable Polymer Brushes for Protein Capture and Release in Biological Environments**
- 2022
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 61:22
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Tidskriftsartikel (refereegranskat)abstract
- Interfaces functionalized with polymers are known for providing excellent resistance towards biomolecular adsorption and for their ability to bind high amounts of protein while preserving their structure. However, making an interface that switches between these two states has proven challenging and concepts to date rely on changes in the physiochemical environment, which is static in biological systems. Here we present the first interface that can be electrically switched between a high-capacity (>1 μg cm−2) multilayer protein binding state and a completely non-fouling state (no detectable adsorption). Switching is possible over multiple cycles without any regeneration. Importantly, switching works even when the interface is in direct contact with biological fluids and a buffered environment. The technology offers many applications such as zero fouling on demand, patterning or separation of proteins as well as controlled release of biologics in a physiological environment, showing high potential for future drug delivery in vivo.
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| 7. |
- Ferrand-Drake Del Castillo, Gustav, 1990, et al.
(författare)
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Enzyme Immobilization in Polyelectrolyte Brushes: High Loading and Enhanced Activity Compared to Monolayers
- 2019
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 35:9, s. 3479-3489
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Tidskriftsartikel (refereegranskat)abstract
- Catalysis by enzymes on surfaces has many applications. However, strategies for efficient enzyme immobilization with preserved activity are still in need of further development. In this work, we investigate polyelectrolyte brushes prepared by both grafting-to and grafting-from with the aim to achieve high catalytic activity. For comparison, self-assembled monolayers that bind enzymes with the same chemical interactions are included. We use the model enzyme glucose oxidase and two kinds of polymers: anionic poly(acrylic acid) and cationic poly(diethylamino)methyl methacrylate. Surface plasmon resonance and spectroscopic ellipsometry are used for accurate quantification of surface coverage. Besides binding more enzymes, the "3D-like" brush environment enhances the specific activity compared to immobilization on self-assembled monolayers. For grafting-from brushes, multilayers of enzymes were spontaneously and irreversibly immobilized without conjugation chemistry. When the pH was between the pI of the enzyme and the pK a of the polymer, binding was considerable (thousands of ng/cm 2 or up to 50% of the polymer mass), even at physiological ionic strength. However, binding was observed also when the brushes were neutrally charged. For acidic brushes (both grafting-to and grafting-from), the activity was higher for covalent immobilization compared to noncovalent. For grafting-from brushes, a fully preserved specific activity compared to enzymes in the liquid bulk was achieved, both with covalent (acidic brush) and noncovalent (basic brush) immobilization. Catalytic activity of hundreds of pmol cm -2 s -1 was easily obtained for polybasic brushes only tens of nanometers in dry thickness. This study provides new insights for designing functional interfaces based on enzymatic catalysis.
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| 8. |
- Ferrand-Drake Del Castillo, Gustav, 1990, et al.
(författare)
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Large Changes in Protonation of Weak Polyelectrolyte Brushes with Salt Concentration-Implications for Protein Immobilization
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:13, s. 5212-5218
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Tidskriftsartikel (refereegranskat)abstract
- We report for the first time that the protonation behavior of weak polyelectrolyte brushes depends very strongly on ionic strength. The pKa changes by one pH step per order of magnitude in salt concentration. For low salt concentrations (∼1 mM), a very high pH is required to deprotonate a polyacidic brush and a very low pH is required to protonate a polybasic brush. This has major consequences for interactions with other macromolecules, as the brushes are actually almost fully neutral when believed to be charged. We propose that many previous studies on electrostatic interactions between polyelectrolytes and proteins have, in fact, looked at other types of intermolecular forces, in particular, hydrophobic interactions and hydrogen bonds.
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| 9. |
- Ferrand-Drake Del Castillo, Gustav, 1990
(författare)
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Polyelectrolyte Brush Electrodes for Protein Capture and Release
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stimuli-responsive polyelectrolyte brushes switch as a function of pH between a charged and neutral state that affects their electrostatic interactions with other charged molecules like proteins. Adjustment of the pH results in the binding of large quantities of proteins making polyelectrolyte brushes widely used as biointerfaces. However, the interaction between proteins and polyelectrolyte brushes remains poorly understood. Protein binding to brushes despite net repulsion indicates that the mechanism is determined by more than electrostatic effects. In this thesis polyelectrolyte brushes, and protein-polyelectrolyte interactions were characterized using new methods. The results show that non-electrostatic interactions play an important role in protein binding to pH-responsive polyelectrolyte brushes. Active switching of polyelectrolyte brushes requires control of the pH. However, controlled pH switching that is convenient and non-invasive has proven difficult to achieve. In this thesis electrochemistry was used to generate local pH gradients, that resulted in reversible switches of polyelectrolyte brushes, even in highly buffered liquids and in biological solutions like serum. Reversible electrochemical switching of polyelectrolyte brushes was accomplished by employing diazonium salt surface functionalization. Electrochemical switching was used to control protein-polyelectrolyte interactions to create polyelectrolyte brush electrodes that captured and released high quantities of proteins on-demand. Our method for electronic control of protein immobilization should increase the utility of pH-stimuli-responsive polymer brushes in applications such as bioanalytics, protein purification, and protein drug-delivery.
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