Molecular recognition at the exterior surface of a zwitterionic telomer brush

Modification of decellularized vascular xenografts with 8-arm polyethylene glycol suppresses macrophage infiltration but maintains graft degradability

Because acellular vascular xenografts induce an immunological reaction through macrophage infiltration, they are conventionally crosslinked with glutaraldehyde (GA). However, the GA crosslinking reaction inhibits not only the host immune reaction around the graft but also the graft's enzymatic degradability, which is one of the key characteristics of acellular grafts that allow them to be replaced by host tissue. In this study, we used an 8-arm polyethylene glycol (PEG) to successfully suppress macrophage infiltration, without eliminating graft degradation. Decellularized ostrich carotid arteries were modified with GA or N-hydroxysuccinimide-activated 8-arm PEG (8-arm PEG-NHS), which has a molecular weight of 17 kDa. To evaluate the enzymatic degradation in vitro, the graft was immersed in a collagenase solution for 12 hr. The 8-arm PEG-modified graft was degraded to the same extent as the unmodified graft, but the GA-modified graft was not degraded. The graft was transplanted into rat subcutaneous tissue for up to 8 weeks. Although CD68-positive cells accumulated in the unmodified graft, they did not infiltrate into either modified graft. However, the GA-modified grafts calcified, but the 8-arm PEG-modified graft did not calcify after transplantation. These data suggested that 8-arm PEG-NHS is a promising modification agent for biodegradable vascular xenografts, to suppress acute macrophage infiltration only.

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

Gold Nanoparticles with Ligand/Zwitterion Hybrid Layer for Individual Counting of Influenza A H1N1 Subtype Using Resistive Pulse Sensing

Resistive pulse sensing (RPS) is an analytical technique for detecting particles with nano- to micrometer diameters, such as proteins, viruses, and bacteria. RPS is a promising tool for diagnosis as it can analyze the characteristics of target particles individually from ion current blockades as pulse waveforms. However, it is difficult to discriminate analog targets because RPS merely provides physical information such as size, shape, concentration, and charge density of the analyte. Influenza A virus, which is 80-120 nm in diameter, has various subtypes, demonstrating the diversity of virus characteristics. For example, highly pathogenic avian influenza infections in humans are recognized as an emerging infectious disease with high mortality rates compared with human influenza viruses. Distinguishing human from avian influenza using their differing biological characteristics would be challenging using RPS. To develop a highly selective diagnostic system for infectious diseases, we combined RPS with molecular recognition. Gold nanoparticles (GNPs) that have human influenza A (H1N1 subtype) virus-specific sialic acid receptors on the surface were prepared as a virus label for RPS analysis. A sulfobetaine and sialic acid (ligand) hybrid surface was formed on the GNPs for the suppression of nonspecific interaction. The results show a size change of viruses derived from specific interactions with GNPs. In contrast, no size shift was observed when nonspecific sialic acid receptor-immobilized GNPs were used. Detection of viruses by individual particle counting could be a new facet of diagnosis.

Romantic Surfaces: A Systematic Overview of Stable, Biospecific, and Antifouling Zwitterionic Surfaces

This Feature Article focuses on recent advances in the bioconjugation of surface-bound zwitterionic polymers for biospecific antifouling surfaces. Various approaches for the functionalization of antifouling zwitterionic polymers are systematically investigated, such as chain-end and side-chain functionalization. Side-chain functionalization methods can be further classified as those that are achieved through homopolymerization of custom-synthesized zwitterionic monomers equipped with reactive groups, or those that are achieved via synthesis of random or block copolymers combining different monomers with antifouling functionality and others with reactive groups. Several of the pros and cons of these approaches are outlined and discussed. Finally, some perspective and future directions of research are presented toward long-term stable, generically repelling surfaces that strongly and specifically adhere to a single component in a complex mixture.

Bioinactive semi-interpenetrating network gel layers: zwitterionic polymer chains incorporated in a cross-linked polymer brush

A thin gel layer with thermo-responsive polymer brushes and semi-interpenetrating PCMB exhibited the switching of bio-inert properties depending on temperature.

Robust nanocoatings based on ionic silicones

Two oppositely charged water-soluble oligosiloxanes with the same main chain were synthesized and used for the formation of multilayer nanocoatings. In spite of low molecular weight of the components, due to entropic reasons, linearly growing and robust films with a hydrophilic surface were formed for the first time. The multilayer films were found to be resistant to high temperature water treatment undergoing only reversible swelling and no surface recovery was observed after prolonged exposure to air indicating permanent water wettability of these silicone-based coatings. High flexibility of the silicone chains resulted in low glass transition temperature (ca. 27 °C) of both dry polyplexes and films as determined using calorimetry and spectroscopic ellipsometry, respectively. Moreover, the thin coating was applied on plasma-treated poly(dimethylsiloxane) preventing surface reconstruction in air and leading to long-lasting hydrophilization of the surface (water contact angles around 65°). Such water-borne systems may be used in common applications of silicones providing high flexibility and at the same time water wettability of the coatings.

A novel approach for UV-patterning with binary polymer brushes

A mixed self-assembled monolayer (SAM) of an initiator (3-(2-bromo-2-isobutyryloxy)propyl triethoxysilane) for atom transfer radical polymerization (ATRP) and an agent (6-(triethoxysilyl)hexyl 2-(((methylthio)carbonothioyl)thio)-2-phenylacetate) for reversible addition-fragmentation chain transfer (RAFT) polymerization was constructed on the surface of a silicon wafer or glass plate by a silane coupling reaction. When a UV light at 254nm was irradiated at the mixed SAM through a photomask, the surface density of the bromine atom at the end of BPE in the irradiated region was drastically reduced by UV-driven scission of the BrC bond, as observed by X-ray photoelectron spectroscopy. Consequently, the surface-initiated (SI)-ATRP of 2-ethylhexyl methacrylate (EHMA) was used to easily construct the poly(EHMA) (PEHMA) brush domain. Subsequently, SI-RAFT polymerization of a zwitterionic vinyl monomer, carboxymethyl betaine (CMB), was performed. Using the sequential polymerization, the PCMB and PEHMA brush domains on the solid substrate could be very easily patterned. Patterning proteins and cells with the binary polymer brush is expected because the PCMB brush indicated strong suppression of protein adsorption and cell adhesion, and the PEHMA brush had non-polar properties. This technique is very simple and useful for regulating the shape and size of bio-fouling and anti-biofouling domains on solid surfaces.

Biodegradable zwitterionic sulfobetaine polymer and its conjugate with paclitaxel for sustained drug delivery

A fully biodegradable zwitterionic polymer and the corresponding conjugate with paclitaxel (PTX) were synthesized as promising biomaterials. Allyl-functionalized polylactide (PLA) was employed as the precursor of polymer backbones. UV-induced thiol-ene reaction was conducted to conjugate thiol-functionalized sulfobetaine (SB) with the PLA-based backbone. The resulting zwitterionic polymer did not exhibit considerable cytotoxicity. A polymer-drug conjugate was also obtained by thiol-ene reaction of both thiol-functionalized SB and PTX with allyl-functionalized PLA. The conjugate could readily form narrowly-dispersed nanoparticles in aqueous solutions with a volume-average hydrodynamic diameter (Dh,V) of 19.3 ± 0.2 nm. Such a polymer-drug conjugate-based drug delivery system showed full degradability, well-suppressed non-specific interaction with biomolecules, and sustained drug release. In vitro assessments also confirmed the significant anti-cancer efficacy of the conjugate. After 72 h incubation with PLA-SB/PTX containing 10 µg/mL of PTX, the cell viabilities of A549, MCF7, and PaCa-2 cells were as low as 20.0 ± 2.5%, 1.7 ± 1.7%, and 14.8 ± 0.9%, respectively. Both flow cytometry and confocal microscopy suggested that the conjugates could be easily uptaken by A549 cells before the major release of PTX moieties. Overall, this work elucidates promising potentials of biodegradable zwitterionic polymer-based materials in biomedical applications.

STATEMENT OF SIGNIFICANCE

The applicability of FDA-approved biodegradable aliphatic polyesters has been significantly restricted because they are hydrophobic and lack functionalities. Recently zwitterionic polymers have emerged as promising hydrophilic biomaterials, but most of the reported zwitterionic polymers are non-biodegradable. This study reports a novel aliphatic polyester-based zwitterionic polymer and the corresponding polymer-drug conjugate. Their aliphatic polyester and zwitterionic components provide them with high enzymatic degradability and low nonspecific interactions with biomolecules, respectively. While the zwitterionic polymer did not show noticeable cytotoxicity, the corresponding polymer-anticancer drug conjugate exhibited acid-sensitive sustained drug release, remarkable effectiveness in killing cancer cells, as well as the ready cellular internalization. This work lays a foundation for the further development of synthetic biodegradable zwitterionic polymer-based materials which potentially may have broad and significant biomedical applications.

Properties of modified surface for biosensing interface

Properties of modified surface, behavior against salting-out effect, suppressive effect for protein nonspecific adsorption, and wettability were examined using various mercapto compounds bearing methyloligoethylene glycol, oligoethylene glycol, alkyl oligoethylene glycol, alkyl phosphoryl choline, alkyl inverse phosphoryl choline, and alkyl sulfobetaine moieties. The behavior against salting-out effect was examined using gold nanoparticle with PBS and NaCl aqueous solution. The suppressive effect for protein nonspecific adsorption was evaluated by SPR, and the wettability was measured on the SPR chip. The gold nanoparticle modified with 8C3EG, 12C4EG, 12CPC, 6CCP, and 12CCP showed excellent behavior against salting-out effect. The suppression of protein nonspecific adsorption was effective with 6EG, 12C4EG, 12CPC, and 12CS. On the other hand, the modified surface possessed high wettability except for the surface modified with M6EG. The results indicate that incorporation of alkyl group into surface modification materials is effective for the enhancement of behavior against salting-out effect and suppressive effect for protein nonspecific adsorption regardless of wettability. Among the zwitter ionic derivatives, inverse phosphoryl choline derivatives showed intriguing properties, high behavior against salting-out effect with high wettability but low suppressive effect for protein nonspecific adsorption.

Surface Modification of PDMS and Plastics with Zwitterionic Polymers

Surface modification of PDMS, polycarbonate, and acrylic resin was examined using various methacryl polymers bearing sulfobetaine, phosphoryl choline, and oligoethylene glycol units. We have found that zwitterionic polymers are adsorbed on the PDMS surface treated with plasma. The surface of PDMS is stable to keep high hydrophilicity after a month of the modification. On the other hand, one of sulfobetaine polymers showed distinguished adsorption behavior in the case of polycarbonate surface treated with plasma. Suppression effect for nonspecific adsorption of BSA was evaluated using polycarbonate and acrylic resin modified with the polymers. The modified surfaces showed suppression effect for nonspecific adsorption of BSA compared with the surface only treated with plasma.

A brief review of recent developments in the designs that prevent bio-fouling on silicon and silicon-based materials

Silicon and silicon-based materials are essential to our daily life. They are widely used in healthcare and manufacturing. However, silicon and silicon-based materials are susceptible to bio-fouling, which is of great concern in numerous applications. To date, interdisciplinary research in surface science, polymer science, biology, and engineering has led to the implementation of antifouling strategies for silicon-based materials. However, a review to discuss those antifouling strategies for silicon-based materials is lacking. In this article, we summarized two major approaches involving the functionalization of silicon and silicon-based materials with molecules exhibiting antifouling properties, and the fabrication of silicon-based materials with nano- or micro-structures. Both approaches lead to a significant reduction in bio-fouling. We critically reviewed the designs that prevent fouling due to proteins, bacteria, and marine organisms on silicon and silicon-based materials. Graphical abstractStrategies used in the designs that prevent bio-fouling on silicon and silicon-based materials.

Control of the primary and secondary structure of polymer brushes by surface-initiated living/controlled polymerization

In this review, we summarize current research regarding the precise synthesis of polymer brushes and characterization methods for their molecular aggregate structure using neutron and/or synchrotron facilities.

Efficient and Tunable Three-Dimensional Functionalization of Fully Zwitterionic Antifouling Surface Coatings

To enhance the sensitivity and selectivity of surface-based (bio)sensors, it is of crucial importance to diminish background signals that arise from the nonspecific binding of biomolecules, so-called biofouling. Zwitterionic polymer brushes have been shown to be excellent antifouling materials. However, for sensing purposes, antifouling does not suffice but needs to be combined with the possibility to efficiently modify the brush with recognition units. So far this has been achieved only at the expense of either antifouling properties or binding capacity. Herein we present a conceptually new approach by integrating both characteristics into a single tailor-made monomer: a novel sulfobetaine-based zwitterionic monomer equipped with a clickable azide moiety. Copolymerization of this monomer with a well-established standard sulfobetaine monomer results in highly antifouling surface coatings with a large yet tunable number of clickable groups present throughout the entire brush. Subsequent functionalization of the azido brushes via widely used strain-promoted alkyne azide click reactions yields fully zwitterionic 3D-functionalized coatings with a recognition unit of choice that can be tailored for any specific application. Here we show a proof of principle with biotin-functionalized brushes on Si₃N₄ that combine excellent antifouling properties with specific avidin binding from a protein mixture. The signal-to-noise ratio is significantly improved over that of traditional chain-end modification of sulfobetaine polymer brushes, even if the azide content is lowered to 1%. This therefore offers a viable approach to the development of biosensors with greatly enhanced performance on any surface.

Sulfobetaine-terminated PEG improves the qualities of an immunosensing surface

Poly(ethylene glycol) (PEG) possessing a sulfobetaine (SB) moiety at one end and a pentaethylenehexamine (N6) at the other end (SB-PEG-N6) was newly synthesized as a blocking agent for immunosensing surfaces. The N6 moiety strongly coordinates on gold surfaces, facilitating the tethering of the PEG chain to the sensor chip surface, and leaves the SB moiety free. Non-specific adsorption of bovine serum albumin (BSA) was analyzed on the SB-PEG-N6 tethered surface and compared with the methoxy-PEG-N6 (M-PEG-N6) tethered surface using a surface plasmon resonance (SPR) sensor. Non-specific BSA adsorption decreased with decreasing PEG chain length on the SB-PEG tethered chain surface. Non-specific adsorption of BSA decreased as ionic strength increased on SB-PEG-N6 surfaces; this phenomenon was completely opposite to that observed with an M-PEG-N6 tethered chain surface. The results show that SB moieties located close to the gold surface perform well with regard to protein rejection. Actually, low-molecular weight alkane thiol SB (SB-SH) showed minimum BSA adsorption. To evaluate protein recognition efficacy on a PEGylated surface, an antibody (IgG) immobilized surface was then constructed on a gold sensor chip using SB-PEG-N6 as the blocking agent. The specific protein recognition efficacy of SB-PEG-N6/IgG co-immobilized surfaces was higher than that obtained using SB-SH/IgG co-immobilized surfaces. We conclude that SB-terminated PEG exhibits the optimal qualities of a blocking agent, as it possesses both high suppression efficacy of nonspecific protein adsorption and specific protein recognition ability.

Thermoresponsive anionic block copolymer brushes with a strongly anionic bottom segment for effective interactions with biomolecules

Thermoresponsive anionic block copolymer brushes were prepared on silica bead surfaces by multistep surface-initiated atom-transfer radical polymerization. The anionic properties of the prepared brushes changed with temperature changes.

Synthesis of catechol and zwitterion-bifunctionalized poly(ethylene glycol) for the construction of antifouling surfaces

Versatile antifouling coatings from catechol and zwitterion-bifunctionalized poly(ethylene glycol).

Protein separations via thermally responsive ionic block copolymer brush layers

Thermoresponsive materials were prepared via multi-step surface-initiated ATRP. Because of the hydrophobic/hydrophilic transitions in the materials, proteins are adsorbed and eluted by simply changing the column temperature.

Responsive inverse opal hydrogels for the sensing of macromolecules

Dual responsive inverse opal hydrogels were designed as autonomous sensor systems for (bio)macromolecules, exploiting the analyte-induced modulation of the opal's structural color. The systems that are based on oligo(ethylene glycol) macromonomers additionally incorporate comonomers with various recognition units. They combine a coil-to-globule collapse transition of the LCST type with sensitivity of the transition temperature toward molecular recognition processes. This enables the specific detection of macromolecular analytes, such as glycopolymers and proteins, by simple optical methods. While the inverse opal structure assists the effective diffusion even of large analytes into the photonic crystal, the stimulus responsiveness gives rise to strong shifts of the optical Bragg peak of more than 100 nm upon analyte binding at a given temperature. The systems' design provides a versatile platform for the development of easy-to-use, fast, and low-cost sensors for pathogens.

Superhydrophilic and underwater superoleophobic poly(sulfobetaine methacrylate)-grafted glass fiber filters for oil-water separation

Oil-water separation is a major problem in industries such as oil production and wastewater treatment, where millions of gallons of oil-contaminated water are produced. Zwitterionic poly(sulfobetaine methacrylate) (pSBMA) is a superhydrophilic polymer due to its strong interaction with water via electrostatic interactions. By coating surfaces of filter media with such a superhydrophilic polymer, it is expected that one can effectively separate oil and water. In this work, pSBMA was grafted onto glass fiber surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP). The in-air water contact angle of the pSBMA-treated glass was 8-15°, as compared to 31° for the control untreated glass, whereas the underwater-oil contact angle of the pSBMA-grafted glass was 162-169°, as compared to 142° for the control pristine glass, suggesting that the pSBMA-grafted glass slides are superhydrophilic and underwater superoleophobic. Such superhydrophilicity and underwater superoleophobicity were realized by modifying surface chemistry only, with no need to create rough surfaces. The pSBMA-grafted glass fiber filters demonstrated exceptional results at separating oil from water without even allowing miniscule amounts of visible oil to permeate through.

Exploiting endocytosis for nanomedicines

In this article, we briefly review the endocytic pathways used by cells, pointing out their defining characteristics and highlighting physical limitations that may direct the internalization of nanoparticles to a subset of these pathways. A more detailed description of these pathways is presented in the literature. We then focus on the endocytosis of nanomedicines and present how various nanomaterial parameters impact these endocytic processes. This topic is an area of active research, motivated by the recognition that an improved understanding of how nanomaterials interact at the molecular, cellular, and whole-organism level will lead to the design of better nanomedicines in the future. Next, we briefly review some of the important nanomedicines already on the market or in clinical development that serve to exemplify how endocytosis can be exploited for medical benefit. Finally, we present some key unanswered questions and remaining challenges to be addressed by the field.

Design and fabrication of biosensing interface for waveguide-mode sensor

In order to develop a biosensing system with waveguide-mode sensor, fabrication of a biosensing interface on the silica surface of the sensing chip was carried out using triethoxysilane derivatives with anti-leptin antibody. Triethoxysilane derivatives bearing succinimide ester and oligoethylene glycol moieties were synthesized to immobilize the antibody and to suppress nonspecific adsorption of proteins, respectively. The chip modified with triethoxysilane derivatives bearing oligoethylene glycol moiety suppressed nonspecific adsorption of proteins derived from human serum effectively by rinse with PBS containing surfactant (0.05% Tween 20). On the other hand, it was confirmed that antibody was immobilized on the chip by immersion into antibody solution to show response of antigen-antibody reaction, where the chip was modified with triethoxysilane derivatives bearing succinimide ester moiety. When the interface was fabricated with antibody and a mixture of triethoxysilane derivatives bearing succinimide ester and oligoethylene glycol moieties, the response of antigen-antibody reaction depended on composition of the mixture and enhanced with the increase of ratio for triethoxysilane derivatives bearing succinimide ester moiety reflecting the antibody concentration immobilized on the chip. While introduction of excess triethoxysilane derivatives bearing succinimide ester moiety induced nonspecific adsorption of proteins derived from human serum, the immobilized antibody on the chip kept its activity after 1-month storage in a refrigerator. Taking into consideration those factors, the biosensing interface was fabricated using triethoxysilane derivatives with anti-leptin antibody to examine performance of the waveguide-mode sensor. It was found that the detection limits for human leptin were 50 ng/mL in PBS and 100 ng/mL in human serum. The results demonstrate that the waveguide-mode sensor powered by the biosensing interface fabricated with those triethoxysilane derivatives and antibody has potential to detect several tens of nanograms per milliliter of biomarkers in human serum with an unlabeled detection method.

Surface modification of a biodegradable magnesium alloy with phosphorylcholine (PC) and sulfobetaine (SB) functional macromolecules for reduced thrombogenicity and acute corrosion resistance

Siloxane functionalized phosphorylcholine (PC) or sulfobetaine (SB) macromolecules (PCSSi or SBSSi) were synthesized to act as surface modifying agents for degradable metallic surfaces to improve acute blood compatibility and slow initial corrosion rates. The macromolecules were synthesized using a thiol-ene radical photopolymerization technique and then utilized to modify magnesium (Mg) alloy (AZ31) surfaces via an anhydrous phase deposition of the silane functional groups. X-ray photoelectron spectroscopy surface analysis results indicated successful surface modification based on increased nitrogen and phosphorus or sulfur composition on the modified surfaces relative to unmodified AZ31. In vitro acute thrombogenicity assessment after ovine blood contact with the PCSSi and SBSSi modified surfaces showed a significant decrease in platelet deposition and bulk phase platelet activation compared with the control alloy surfaces. Potentiodynamic polarization and electrochemical impedance spectroscopy data obtained from electrochemical corrosion testing demonstrated increased corrosion resistance for PCSSi- and SBSSi-modified AZ31 versus unmodified surfaces. The developed coating technique using PCSSi or SBSSi showed promise in acutely reducing both the corrosion and thrombotic processes, which would be attractive for application to blood contacting devices, such as vascular stents, made from degradable Mg alloys.

Block copolymer modified surfaces for conjugation of biomacromolecules with control of quantity and activity

Polymer brush layers based on block copolymers of poly(oligo(ethylene glycol) methacrylate) (POEGMA) and poly(glycidyl methacrylate) (PGMA) were formed on silicon wafers by activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). Different types of biomolecule can be conjugated to these brush layers by reaction of PGMA epoxide groups with amino groups in the biomolecule, while POEGMA, which resists nonspecific protein adsorption, provides an antifouling environment. Surfaces were characterized by water contact angle, ellipsometry, and Fourier transform infrared spectroscopy (FTIR) to confirm the modification reactions. Phase segregation of the copolymer blocks in the layers was observed by AFM. The effect of surface properties on protein conjugation was investigated using radiolabeling methods. It was shown that surfaces with POEGMA layers were protein resistant, while the quantity of protein conjugated to the diblock copolymer modified surfaces increased with increasing PGMA layer thickness. The activity of lysozyme conjugated on the surface could also be controlled by varying the thickness of the copolymer layer. When biotin was conjugated to the block copolymer grafts, the surface remained resistant to nonspecific protein adsorption but showed specific binding of avidin. These properties, that is, well-controlled quantity and activity of conjugated biomolecules and specificity of interaction with target biomolecules may be exploited for the improvement of signal-to-noise ratio in sensor applications. More generally, such surfaces may be useful as biological recognition elements of high specificity for functional biomaterials.

Molecular recognition: from solution science to nano/materials technology

In the 25 years since its Nobel Prize in chemistry, supramolecular chemistry based on molecular recognition has been paid much attention in scientific and technological fields. Nanotechnology and the related areas seek breakthrough methods of nanofabrication based on rational organization through assembly of constituent molecules. Advanced biochemistry, medical applications, and environmental and energy technologies also depend on the importance of specific interactions between molecules. In those current fields, molecular recognition is now being re-evaluated. In this review, we re-examine current trends in molecular recognition from the viewpoint of the surrounding media, that is (i) the solution phase for development of basic science and molecular design advances; (ii) at nano/materials interfaces for emerging technologies and applications. The first section of this review includes molecular recognition frontiers, receptor design based on combinatorial approaches, organic capsule receptors, metallo-capsule receptors, helical receptors, dendrimer receptors, and the future design of receptor architectures. The following section summarizes topics related to molecular recognition at interfaces including fundamentals of molecular recognition, sensing and detection, structure formation, molecular machines, molecular recognition involving polymers and related materials, and molecular recognition processes in nanostructured materials.

Endocytosis at the nanoscale

Endocytosis is a fundamental process in which eukaryotic cells internalise molecules and macromolecules via deformation of the membrane and generation of membrane-bound carriers. Functional aspects are not only limited to uptake of nutrients, but also play a primary role in evolutionary conserved processes such as the regulation of plasma membrane protein activity (i.e. signal-transducing receptors, small-molecule transporters and ion channels), cell motility and mitosis. The macromolecular nature of the material transported by endocytosis makes this route one of the most important targets for nanomedicine. Indeed, many nanoparticle formulations have been customised to enter cells through endocytosis and deliver the cargo within the cell. In this critical review, we present an overview of the biology of endocytosis and discuss its implications in cell internalisation of nanoparticles. We discuss how nanoparticle size, shape and surface chemistry can control this process effectively. Finally, we discuss different drug delivery strategies on how to evade lysosomal degradation to promote effective release of the cargo (376 references).

Bioconjugation of protein-repellent zwitterionic polymer brushes grafted from silicon nitride

A new method for attaching antibodies to protein-repellent zwitterionic polymer brushes aimed at recognizing microorganisms while preventing the nonspecific adsorption of proteins is presented. The poly(sulfobetaine methacrylate) (SBMA) brushes were grafted from α-bromo isobutyryl initiator-functionalized silicon nitride (Si(x)N(4), x ≥ 3) surfaces via controlled atom-transfer radical polymerization (ATRP). A trifunctional tris(2-aminoethyl)amine linker was reacted with the terminal alkylbromide of polySBMA chains. N-Hydroxysuccinimide (NHS) functionalization was achieved by reacting the resultant amine-terminated polySBMA brush with bifunctional suberic acid bis(N-hydroxysuccinimide ester). Anti-Salmonella antibodies were subsequently immobilized onto polySBMA-grafted Si(x)N(4) surfaces through these NHS linkers. The protein-repellent properties of the polySBMA-grafted surface after antibody attachment were evaluated by exposing the surfaces to Alexa Fluor 488-labeled fibrinogen (FIB) solution (0.1 g·L(-1)) for 1 h at room temperature. Confocal laser scanning microscopy (CLSM) images revealed the minimal adsorption of FIB onto the antibody-coated polySBMA in comparison with that of antibody-coated epoxide monolayers and also bare Si(x)N(4) surfaces. Subsequently, the interaction of antibodies immobilized onto polySBMA with SYTO9-stained Salmonella solution without using blocking solution was examined by CLSM. The fluorescent images showed that antibody-coated polySBMA efficiently captured Salmonella with only low background noise as compared to antibody-coated monolayers lacking the polymer brush. Finally, the antibody-coated polySBMA surfaces were exposed to a mixture of Alexa Fluor 647-labeled FIB and Salmonella without the prior use of a blocking solution to evaluate the ability of the surfaces to capture bacteria while simultaneously repelling proteins. The fluorescent images showed the capture of Salmonella with no adsorption of FIB as compared to antibody-coated epoxide surfaces, demonstrating the potential of the zwitterionic layer in preventing the nonspecific adsorption of the proteins during the detection of bacteria in complex matrices.