Brush Nanostructures Research Articles

The Architecture of Oligonucleotide‐Polycationic Brush Complexes – A Neutron Reflectometry Study

AbstractPolycationic brushes are attractive systems for the design of nanomaterials for gene delivery as they enable rational design of their architecture with a broad range of grafting densities, thicknesses, and chemistries. Recently, their performance for siRNA delivery is highlighted and the strong impact of their molecular architecture on RNA binding and transfection efficiency now calls for a greater understanding of the architecture of polymer brush‐oligonucleotide complexes. In this study, the morphology of polymer brushes with a range of grafting densities, thicknesses, and chemistry (weak polybase poly(dimethylaminoethyl methacrylate), PDMAEMA, and strong poly(2‐methacrylolyloxyethyltrimethylammonium iodide), PMETAI) and their complexes with 20 base pair siRNA oligonucleotides are first investigated. These assemblies are then studied via neutron reflectometry, building first a model of brush swelling in deionized water, at three different contrasts, prior to the investigation of brush‐RNA complexes. It is found that oligonucleotides infiltrate deep within the brush and alter the morphology of their most basal layer more strongly, regardless of the strength of the polybase. This understanding will enable the improved rational design of polymer brush nanostructures for gene delivery applications.

Precise positioning of enzymes within hierarchical polymer nanostructures for switchable bioelectrocatalysis

The ability to reversibly switch bioelectrocatalytic sensors is attractive for the design of biomonitoring platforms displaying a complex environmental response, or for the protection of biosensors. However, the retention of reversible biocatalytic properties upon multiple environmental cycles, with broad detection range, low signal-to-noise and limit of detection remains challenging. In this report, we demonstrate the precise positioning of the enzyme glucose oxidase within block-copolymer brush nanostructures, via the re-initiation of N-isopropylacrylamide (NIPAM) polymerisation from enzyme-decorated poly(dimethylaminoethyl methacrylate) (PDMAEMA) blocks. We find that the precise design of polymer brush grafting density, thickness and crosslinking of the PNIPAM block enables the stable positioning of biocatalytic sites close to electrode surfaces. The control of the polymer brush nanostructure, its conformation and the distribution of biocatalytic sites is characterised via a combination of in situ ellipsometry, X-ray photoelectron spectroscopy, grazing angle FTIR and surface plasmon resonance. In turn, cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that such control of the polymeric nanostructures confers a unique combination of low limit of detection (23.9μM), a broad dynamic range of glucose sensing (0.05-12.8mM) and true "OFF" state upon pH or thermal stimulation, whilst retaining excellent performance over repeated switching cycles of the sensor. Therefore, hierarchical biocatalytic polymer brushes display unique properties for the design of responsive biosensors and complex multi-functional gating platforms.

Terraced and Smooth Gradient Polymer Brushes via a Polymer Single‐Crystal Assisted Grafting‐To Method

AbstractGradient polymer brushes provide a spatial gradient change in molecular characteristics of the brush, and such a change can be utilized to study structure–property relationships in a combinatorial fashion. In this study, a bottom‐up method was used to synthesize gradient polymer brushes with a predesigned and precisely controlled grafting density gradient and brush pattern. A polymer single‐crystal assisted grafting‐to (PSCAGT) method was employed where end‐functionalized polymers were grown into two‐dimensional polymer single crystals. The latter were chemically coupled to a solid substrate to form well‐defined polymer brushes. To tune the grafting density, end‐dissimilar polymers were used to co‐crystallize into one single crystal. Programmed single‐crystal growth was introduced to synthesize brushes with two different gradient architectures, that is, terraced and smooth gradient with pyramid patterns. This work demonstrates that the PSCAGT method offers a unique means to tune polymer brush nanostructure.

Terraced and Smooth Gradient Polymer Brushes via a Polymer Single-Crystal Assisted Grafting-To Method.

Gradient polymer brushes provide a spatial gradient change in molecular characteristics of the brush, and such a change can be utilized to study structure-property relationships in a combinatorial fashion. In this study, a bottom-up method was used to synthesize gradient polymer brushes with a predesigned and precisely controlled grafting density gradient and brush pattern. A polymer single-crystal assisted grafting-to (PSCAGT) method was employed where end-functionalized polymers were grown into two-dimensional polymer single crystals. The latter were chemically coupled to a solid substrate to form well-defined polymer brushes. To tune the grafting density, end-dissimilar polymers were used to co-crystallize into one single crystal. Programmed single-crystal growth was introduced to synthesize brushes with two different gradient architectures, that is, terraced and smooth gradient with pyramid patterns. This work demonstrates that the PSCAGT method offers a unique means to tune polymer brush nanostructure.

Ubiquitous element approach to plasmonic enhanced photocatalytic water splitting: the case of Ti@TiO2 core-shell nanostructure

We demonstrate a new approach to plasmonic enhanced photocatalytic water splitting by developing a novel core-shell Ti@TiO2 brush nanostructure where an elongated Ti nanorod forms a plasmonic core that concentrates light inside of a nanotubular anodic TiO2 shell. Following the ubiquitous element approach aimed at providing an enhanced device functionality without the usage of noble or rare earth elements, we utilized only inexpensive Ti to create a complex Ti@TiO2 nanostructure with an enhanced UV and Vis photocatalytic activity that emerges from the interplay between the surface plasmon resonance in the Ti core, Vis light absorption in the Ti-rich oxide layer at the Ti/TiO2 interface and UV light absorption in the nanotubular TiO2 shell.

Smart polymer brush nanostructures guide the self-assembly of pore-spanning lipid bilayers with integrated membrane proteins

Nanopores in arrays on silicon chips are functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes and used as supports for pore-spanning lipid bilayers with integrated membrane proteins. Robust platforms are created by the covalent grafting of polymer brushes using surface-initiated atom transfer radical polymerization (ATRP), resulting in sensor chips that can be successfully reused over several assays. His-tagged proteins are selectively and reversibly bound to the nitrilotriacetic acid (NTA) functionalization of the PMAA brush, and consequently lipid bilayer membranes are formed. The enhanced membrane resistance as determined by electrochemical impedance spectroscopy and free diffusion of dyed lipids observed as fluorescence recovery after photobleaching confirmed the presence of lipid bilayers. Immobilization of the His-tagged membrane proteins on the NTA-modified PMAA brush near the pore edges is characterized by fluorescence microscopy. This system allows us to adjust the protein density in free-standing bilayers, which are stabilized by the polymer brush underneath. The potential application of the integrated platform for ion channel protein assays is demonstrated.

Fabrication of Complex Three‐Dimensional Polymer Brush Nanostructures through Light‐Mediated Living Radical Polymerization

Ein einfacher Zugang zu gemusterten 3D-Polymerbürsten basiert auf einer durch sichtbares Licht angeregten radikalischen Polymerisation. Die zeitliche und örtliche Kontrolle der Polymerisation ermöglicht die Musterung der Polymerbürsten ausgehend von einer einheitlichen Initiatorschicht durch eine einfache Photomaske (siehe Bild). Durch Änderung der Lichtintensität können unter anderem gemusterte Polymerblöcke und komplexe 3D-Strukturen aufgebaut werden.

Fabrication of Complex Three‐Dimensional Polymer Brush Nanostructures through Light‐Mediated Living Radical Polymerization

Fabrication of Complex Three‐Dimensional Polymer Brush Nanostructures through Light‐Mediated Living Radical Polymerization

ZnO/TiO2 core–brush nanostructure: processing, microstructure and enhanced photocatalytic activity

Heterostructure ZnO/TiO2 core–brush nanostructures were synthesized on glass substrates by a combination of aqueous solution growth and magnetron sputtering method. The microstructure and morphology were characterized using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The heterostructure core–brush shows the single crystal ZnO nanorod as the core and polycrystalline TiO2 nanowires as the brush-like outer layer. Surface electronic states and optical transmittance were measured using X-ray photoelectron spectroscopy and a UV-vis spectrometer. The growth mechanism was proposed as a slow “particle-by-particle” mechanism. The photocatalytic activity of the ZnO/TiO2 core–brush nanostructure was evaluated by the decomposition reaction of Bromo-Pyrogallol Red dye under UV (245 nm) and visible-light (450 nm) irradiation. The results revealed that the core–brush structure exhibited much higher photocatalytic activities than that of a TiO2 film and a TiO2/ZnO composite film. The photocatalytic activity enhancement of the ZnO/TiO2 core–brush could be attributed to the interaction effect, lower band gap energy and its unique core–brush feature which can lower the recombination rate of electron–hole pairs, extend the absorption range and provide a high density of active sites.

Nanostructured Polymer Brushes by UV‐Assisted Imprint Lithography and Surface‐Initiated Polymerization for Biological Functions

AbstractFunctional polymer brush nanostructures are obtained by combining step‐and‐flash imprint lithography (SFIL) with controlled, surface‐initiated polymerization (CSIP). Patterning is achieved at length scales such that the smallest elements have dimensions in the sub‐100 nm range. The patterns exhibit different shapes, including lines and pillars, over large surface areas. The platforms obtained are used to selectively immobilize functional biomacromolecules. Acrylate‐based polymer resist films patterned by SFIL are first used for the selective immobilization of ATRP silane‐based initiators, which are coupled to unprotected domains of silicon substrates. These selectively deposited initiators are then utilized in the controlled radical SIP of poly(ethylene glycol)methacrylates (PEGMA). Nanostructured brush surfaces are then obtained by removal of the resist material. The areas previously protected by the SFIL resist are passivated by inert, PEG‐based silane monolayers following resist removal. PEGMA brush nanostructures are finally functionalized with biotin units in order to provide selective attachment points for streptavidin proteins. Atomic force microscopy and fluorescence spectroscopy confirm the successful immobilization of streptavidin molecules on the polymer grafts. Finally, it is demontrated that this fabrication method allows the immobilization of a few tens of protein chains attached selectively to brush nanostructures, which are surrounded by nonfouling PEG‐functionalized areas.

PH Responsive Polymeric Brush Nanostructures: Preparation and Characterization by Scanning Probe Oxidation and Surface Initiated Polymerization

pH-responsive PHEMA-based polymeric nanostructures were grown in a controlled manner by ATRP-based surface-initiated polymerization. Initiator nanopatterns were obtained on silicon wafers covered with OTS resists made by AFM scanning probe oxidation lithography. AFM images confirmed isolated grafting of stimuli-responsive hedge and dot brush structures exhibiting dimensions corresponding to a few tens of chains.

Polymeric and biomacromolecular brush nanostructures: progress in synthesis, patterning and characterization

A significant scientific and engineering challenge of recent years has been the fabrication of patterned polymeric and biomacromolecular brush nanostructures on surfaces. These structures provide researchers with a rich platform on which to exploit and observe nanoscale phenomena. In this review we present an overview of the field and highlight, through selected examples, recent advances in the nanostructuring of polymer and biomacromolecular brushes. This includes a brief overview of polymer brush synthesis techniques and how these are integrated with nanolithographic and templating approaches. We discuss the characterization of polymeric nanostructures and its associated difficulties, and we provide some perspective of how we see the future direction of the field evolving.

Chemical growth of ZnO nanorod arrays on textured nanoparticle nanoribbons and its second-harmonic generation performance

On the basis of the highly oriented ZnO nanoparticle nanoribbons as the growth seed layer (GSL) and solution growth technique, we have synthesized vertical ZnO nanorod arrays with high density over a large area and multi-teeth brush nanostructure, respectively, according to the density degree of the arrangement of nanoparticle nanoribbons GSL on the glass substrate. This controllable and convenient technique opens the possibility of creating nanostructured film for industrial fabrication and may represent a facile way to get similar structures of other compounds by using highly oriented GSL to promote the vertical arrays growth. The growth mechanism of the formation of the ordered nanorod arrays is also discussed. The second-order nonlinear optical coefficient d 31 of the vertical ZnO nanorod arrays measured by the Maker fringes technique is 11.3 times as large as that of d 36 KH 2PO 4 (KDP).

Critical Brush Density for the Transition between Carpet-Only and Carpet/Brush Double-Layered Structures1

The critical brush density, where transition from carpet-only structure to carpet/brush double-layered structure occurs, was estimated for a weakly ionic amphiphilic diblock copolymer, (diethylsilacyclobutane)34-b-(methacrylic acid)50, monolayer on water by an in situ X-ray reflectivity technique. The brush density in the monolayer was controlled from 0.11 to 0.60 brush chain/nm2 by changing surface pressure and mixing a poly(diethylsilacyclobutane) homopolymer separately synthesized. Only a carpet layer was formed at a low brush density condition, but a carpet and brush double layer was found for a higher brush density of more than 0.48/nm2. This brush density, which is fairly high, would be valuable for discussing the polyelectrolyte brush nanostructure.

Synthesis and nanostructure of strong polyelectrolyte brushes in amphiphilic diblock copolymer monolayers on a water surface.

We synthesized an ionic amphiphilic diblock copolymer, poly(hydrogenated isoprene)-b-poly(styrenesulfonic acid) (PIp-h2-b-PSS), by living anionic polymerization, and the nanostructure of its monolayer spread on a water surface was directly investigated by the in situ X-ray reflectivity technique. The monolayer of the diblock copolymer on a water surface had a smooth hydrophobic PIp-h2 layer on water and a "carpet"/polymer brush double layer in a hydrophilic sodium polystyrene sulfonate (PSSNa) layer under the water. The surface pressure dependence and PSSNa chain length dependence of the PIp-h2 layer thickness and the brush nanostructure were quantitatively studied. The effect of salt concentration in the subphase was also investigated in aqueous solutions containing 0-2 M NaCl. The salt effect on monolayer structure occurred at around 0.2 M. The thickness of the PSS brush layer decreased at salt concentrations above 0.2 M, while no structural change was observed below 0.2 M. This critical salt concentration is thought to be related to the balance of ionic concentrations inside the brush and in bulk solution.