| 1. |
- Wang, Xiaohua, et al.
(författare)
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Electric-Field-Assisted Dip-Pen Nanolithography on Poly(4-vinylpyridine) (P4VP) Thin Films
- 2010
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 2:10, s. 2904-2909
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Tidskriftsartikel (refereegranskat)abstract
- Dip-pen nanolithography (DPN) has attracted increased attention for its ability to generate nanometer-scale patterns on solid surface using an “ink”-coated atomic force microscope (AFM) tip. In contrast to this conventional anchoring-molecules procedure, nanopatterns can also be created by triggering the structural response of the proper substrate. In one approach, the delivery of acidic buffer from the tip into a poly(4-vinylpyridine) (P4VP) thin film (while the tip is being laterally moved, in a raster fashion, along a preprogrammed pattern) leads to the polymer swelling in response to the local protonation. This practice, however, has suffered from a lack of consistency due to the potentially many factors influencing the pattern formation. Herein we report that a more reliable strategy for well controlling the protonation process results when applying an electric held between the AFM tip and the sample. We demonstrate the improved capabilities of the electric-field-assisted DPN method towards reproducibly and reliably fabricating nanostructures by taking advantage of the responsive characteristics (i.e. swelling) of P4VP. Our work includes a systematic study of pattern fabrication under different patterning parameters (mainly the applied bias and contact force) and, very important, provides evidence of the reversible characteristic of the pattern formation process.
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| 2. |
- Deng, Lingquan, et al.
(författare)
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Stereocontrolled 1-S-glycosylation and comparative binding studies of photoprobe-thiosaccharide conjugates with their O-linked analogs
- 2013
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Ingår i: Pure and Applied Chemistry. - 0033-4545 .- 1365-3075. ; 85:9, s. 1789-1801
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Tidskriftsartikel (refereegranskat)abstract
- The use of thioglycosides and other glycan derivatives with anomeric sulfur linkages is gaining increasing interest, both in synthesis and in various biological contexts. Herein, we demonstrate the occurrence and circumvention of anomerization during 1-S-glycosylation reactions, and present highly efficient and stereocontrolled syntheses of a series of photoprobe-thiosaccharide conjugates. Mutarotation of glycosyl thiols proved to be the origin of the anomeric mixtures formed, and kinetic effects could be used to circumvent anomerization. The synthesized carbohydrate conjugates were then evaluated by both solution- and solid-phase-based techniques. Both binding results showed that the S-linked glycosides interact with their cognate lectins comparably to the corresponding O-analogs in the present cases, thus demonstrating the reliability of the solid-support platform built upon our photo-initiated carbohydrate immobilization method for probing protein bindings, and showing the potential of combining these two means for studying carbohydrate-protein inter-actions.
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| 3. |
- Kubo, Takuya, et al.
(författare)
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Polymer-based photocoupling agent for the efficient immobilization of nanomaterials and small molecules
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:15, s. 9372-9378
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Tidskriftsartikel (refereegranskat)abstract
- A highly efficient photocoupling agent, based on perfluorophenylazide (PFPA)-conjugated polyallylamine (PAAm), was developed for the efficient immobilization of polymers, nanoparticles, graphene, and small molecules. The conjugate, PAAm–PFPA, was synthesized, and the percentage of the photoactive moiety, PFPA, can be controlled by the ratio of the two components in the synthesis. By treating epoxy-functionalized wafers with PAAm–PFPA, photoactive surfaces were generated. Compared with the PFPA surface, these polymer-based photocoupling matrix resulted in significantly enhanced immobilization efficiencies, especially for nanomaterials and small molecules. Thus, polystyrene nanoparticles (PS NPs) and alkyl-functionalized silica nanoparticles (SNPs) were successfully immobilized on the PAAm–PFPA surface, resulting in a high material density. Graphene flakes patterned on the PAAm–PFPA surface showed improved feature resolution in addition to a higher material density compared to that of flakes immobilized on the PFPA surface. Furthermore, 2-O-α-d-mannopyranosyl-d-mannopyranose (Man2) immobilized on the PAAm–PFPA surface exhibited significantly enhanced signals when treated with lectin concanavalin A (Con A).
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| 4. |
- Tyagi, Anuradha, et al.
(författare)
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Photogenerated carbohydrate microarrays to study carbohydrate-protein interactions using surface plasmon resonance imaging
- 2010
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Ingår i: Biosensors & bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 26:2, s. 344-350
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Tidskriftsartikel (refereegranskat)abstract
- A photochemical strategy to generate carbohydrate microarrays on flat sensor surfaces, and to study the protein-binding effects of these arrays by surface plasmon resonance imaging is described. The approach was validated using a panel of carbohydrate-binding proteins. The coupling agents, thiol-functionalized perfluorophenyl azides, allow the covalent attachment of underivatized carbohydrates to gold surfaces by a fast photochemical reaction. Carbohydrate microarrays composed of 3,6-di-O-(alpha-D-mannopyranosyl)-D-mannopyranose (Man3), 2-O-alpha-D-mannopyranosyl-D-mannopyranose (Man2), D-mannose (Man), D-glucose (Glc), and D-galactose (Gal) were constructed, and the binding studies were carried out in real-time using surface plasmon resonance imaging. Results showed that the immobilized carbohydrate ligands retained their binding affinities with lectins, the rank order of which was consistent with that of the free ligands in solution. The detection limit of Man3, Man2, Man, and Glc with the lectin Concanavalin A was measured to be 0.29 nM, 0.18 nM, 0.61 nM, and 3.1 nM, respectively. In addition, soybean agglutinin and Griffonia simplicifolia lectin II were tested on the array, and the results were consistent with the binding selectivity of these lectins with the carbohydrate ligands.
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| 5. |
- Wang, Xin, et al.
(författare)
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A photochemically initiated chemistry for coupling underivatized carbohydrates to gold nanoparticles
- 2009
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 19:47, s. 8944-8949
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Tidskriftsartikel (refereegranskat)abstract
- The sensitive optoelectronic properties of metal nanoparticles make nanoparticle-based materials a powerful tool to study fundamental biorecognition processes. Here we present a new and versatile method for coupling underivatized carbohydrates to gold nanoparticles (Au NPs) via the photochemically induced reaction of perfluorophenylazide (PFPA). A one-pot procedure was developed where Au NPs were synthesized and functionalized with PFPA by a ligand-exchange reaction. Carbohydrates were subsequently immobilized on the NPs by a fast light activation. The coupling reaction was efficient, resulting in high coupling yield as well as high ligand surface coverage. A colorimetric system based on the carbohydrate-modified Au NPs was used for the sensitive detection of carbohydrate-protein interactions. Binding and cross-reactivity studies were carried out between carbohydrate-functionalized Au NPs and lectins. Results showed that the surface-bound carbohydrates not only retained their binding affinities towards the corresponding lectin, but also exhibited affinity ranking consistent with that of the free ligands in solution.
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| 6. |
- Wang, Xin, et al.
(författare)
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Direct Measurement of Glyconanoparticles and Lectin Interactions by Isothermal Titration Calorimetry
- 2012
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 84:10, s. 4248-4252
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Tidskriftsartikel (refereegranskat)abstract
- Glyconanomaterials have shown high potential in applications including bioanalysis and nanomedicine. Here, a quantitative analytical technique, based on isothermal titration calorimetry, was developed to characterize the interactions between glyconanoparticles and lectins. By titrating lectins into the glyconanoparticle solution, the apparent dissociation constant, thermodynamic parameters, and the number of binding sites were derived simultaneously. For the glyconanoparticles-lectin binding pairs investigated, a 3-5 order of magnitude affinity enhancement over the free ligand-lectin interactions was observed which can be attributed to the multivalent ligand presentation on the nanoparticles. The impact of ligand density was also studied, and results showed that the affinity increased with the number of glycans on the nanoparticle.
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| 7. |
- Wang, Xin, et al.
(författare)
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Dye-doped silica nanoparticles as efficient labels for glycans
- 2011
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 47:14, s. 4261-4263
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Tidskriftsartikel (refereegranskat)abstract
- We report that dye-doped fluorescent silica nanoparticles (FSNPs) are highly efficient labels for glycans. Mono- and oligo-saccharides were conjugated to FSNPs using a general photocoupling chemistry. FSNP-labeled glycans were applied to image and detect bacteria, and to study carbohydrate-lectin interactions on a lectin microarray.
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| 8. |
- Wang, Xin, et al.
(författare)
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Dynamic light scattering as an efficient tool to study glyconanoparticle-lectin interactions
- 2011
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 136:20, s. 4174-4178
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Tidskriftsartikel (refereegranskat)abstract
- Glyconanomaterials, an emerging class of bio-functional nanomaterials, have shown promise in detecting, imaging and targeting proteins, bacteria, and cells. In this article, we report that dynamic light scattering (DLS) can be used as an efficient tool to study glyconanoparticle (GNP)-lectin interactions. Silica and Au nanoparticles (NPs) conjugated with D-mannose (Man) and D-galactose (Gal) were treated with the lectins Concanavalin A (Con A) and Ricinus communis agglutinin (RCA(120)), and the hydrodynamic volumes of the resulting aggregates were measured by DLS. The results showed that the particle size grew with increasing lectin concentration. The limit of detection (LOD) was determined to be 2.9 nM for Con A with Man-conjugated and 6.6 nM for RCA(120) with Gal-conjugated silica NPs (35 nm), respectively. The binding affinity was also determined by DLS and the results showed 3-4 orders of magnitude higher affinity of GNPs than the free ligands with lectins. The assay sensitivity and affinity were particle size dependent and decreased with increasing particle diameter. Because the method relies on the particle size growth, it is therefore general and can be applied to nanomaterials of different compositions.
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| 9. |
- Wang, Xin, et al.
(författare)
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Engineering Nanomaterial Surfaces for Biomedical Applications
- 2009
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Ingår i: Experimental biology and medicine. - : SAGE Publications. - 1535-3702 .- 1535-3699. ; 234:10, s. 1128-1139
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Tidskriftsartikel (refereegranskat)abstract
- Nanomaterials, possessing unique physical and chemical properties, have attracted much interest and generated wide varieties of applications. Recent investigations of functionalized nanomaterials have expanded into the biological area, providing a versatile platform in biomedical applications such as biomolecular sensing, biological imaging, drug delivery and disease therapy. Bio-functions and bio-compatibility of nanomaterials are realized by introducing synthetic ligands or natural biomolecules onto nanomaterials, and combining ligand-receptor biological interactions with intrinsic nanomaterial properties. Common strategies of engineering nanomaterial surfaces involve physisorption or chemisorption of desired ligands. We developed a phollochemically initiated surface coupling chemistry, bringing versatility and simplicity to nanomaterial functionalization. The method was applied to attach underivatized carbohydrates efficiently on gold and iron oxide nanoparticles, and the resulting glyconanoparticles were successfully used as a sensitive biosensing system probing specific interactions between carbohydrates and proteins as well as bacteria. Exp Biol Med 234:1128-1139, 2009
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| 10. |
- Wang, Xin, et al.
(författare)
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Glyconanomaterials : Synthesis, Characterization, and Ligand Presentation
- 2010
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 22:17, s. 1946-1953
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Tidskriftsartikel (refereegranskat)abstract
- Glyconanomaterials, nanomaterials carrying surface-tethered carbohydrate ligands, have emerged and demonstrated increasing potential in biomedical imaging, therapeutics, and diagnostics. These materials combine the unique properties of nanometer-scale objects with the ability to present multiple copies of carbohydrate ligands, greatly enhancing the weak affinity of individual ligands to their binding partners. Critical to the performance of glyconanomaterials is the proper display of carbohydrate ligands, taking into consideration of the coupling chemistry, the type and length of the spacer linkage, and the ligand density. This article provides an overview of the coupling chemistry for attaching carbohydrate ligands to nanomaterials, and discusses the need for thorough characterization of glyconanomaterials, especially quantitative analyses of the ligand density and binding affinities. Using glyconanoparticles synthesized by a versatile photocoupling chemistry, methods for determining the ligand density by colorimetry and the binding affinity with lectins by a fluorescence competition assay are determined. The results show that the multivalent presentation of carbohydrate ligands significantly enhances the binding affinity by several orders of magnitude in comparison to the free ligands in solution. The effect is sizeable even at low surface ligand density. The type and length of the spacer linkage also affect the binding affinity, with the longer linkage promoting the association of bound ligands with the corresponding lectins.
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