Precise Size‐Selective Sieving of Nanoparticles Using a Highly Oriented Two‐Dimensional Supramolecular Polymer

The development of size‐selective membranes with well‐defined nanopores towards the precise separation of nanometer‐sized substances is a challenging task to achieve. Here a supramolecular membrane is presented that comprises a highly oriented, honeycomb‐like, 2D supramolecular polymer on a polycarbonate filter support. It enables precise size‐selective sieving of colloidal nanoparticles (NPs). Owing to the uniform parallel‐aligned nanocavities within the 2D supramolecular polymers, the composite membrane shows a high size‐selectivity with a sub‐nanometer accuracy in the cutoff size of about 4.0 nm. In principle, the species of size‐separable particles are unlimited, as demonstrated by quantum dots, noble metal, and metal oxide NPs. This supramolecular membrane combined with filtration advances the potential of NPs in terms of their monochromatic emission and size monodispersity, and also enables rapid removal of small magnetic NP adsorbents that are otherwise difficult to capture.     

Cationic Salt‐Responsive Bottle‐Brush Polymers

A class of cationic bottle‐brush polymers that show ionic strength‐dependent stimuli responsiveness is prepared. Brush polymers with norbornene as backbone and quaternary ammonium (QA)‐containing polycaprolactone copolymers as side chains are synthesized by a combination of ring‐opening metathesis polymerization, ring‐opening polymerization, and click reaction. In water with low ionic strength, brush polymers are soluble due to the strong electrostatic repulsion between cationic QA groups. As the addition of salt to increase ionic strength, single brush polymers undergo a transition from extended conformation to collapsed state and finally become insoluble in solution due to the screening effect of salts that yield the once‐dominant electrostatic interactions among QA species to hydrophobic–hydrophobic interactions.

     

Hydrophilic polymer foams with well‐defined open‐cell structure prepared from pickering high internal phase emulsions

Open‐cell hydrophilic polymer foams are prepared through oil‐in‐water Pickering high internal phase emulsions (HIPEs). The Pickering HIPEs are stabilized by commercial titania (TiO₂) nanoparticles with adding small amounts of non‐ionic surfactant Tween85. The morphologies, such as average void diameter and interconnectivity, of the foams can be tailored easily by varying the TiO₂ nanoparticles and Tween85 concentrations. Further, investigation of the HIPE stability, emulsion structure and the location of TiO₂ nanoparticles in resulting foams shows that the surfactant tends to occupy the oil‐water interface at the contact point of adjacent droplets, where the interconnecting pores are hence likely to be formed after the consolidation of the continuous phase. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Solvent‐Responsive Behavior of Polymer‐Brush‐Modified Amphiphilic Gold Nanoparticles

Amphiphilic polymer brushes grafted onto gold nanoparticles impart distinct solvent‐responsive behavior via the change to particle size and surface chemistry and, therefore, wide application prospects can be expected. Coarse‐grained simulations are performed for block and/or mixed polystyrene (PS)/poly(ethylene oxide) (PEO)‐modified amphiphilic gold nanoparticles (AuNP) to investigate their responsive behavior in five different solvents by analyzing their morphology, distribution density profiles, and gyration radii. Typical core–shell, Janus‐type, buckle‐like, ring‐like, jellyfish‐like, and octopus‐like morphologies are formed. Influence of block sequence, mixing mode, and several other effects are discussed. Responsive particle size and surface hydrophilicity can be successfully reproduced by altering solvents.

     

Salt‐Driven Deposition of Thermoresponsive Polymer‐Coated Metal Nanoparticles on Solid Substrates

Here we report on a simple, generally applicable method for depositing metal nanoparticles on a wide variety of solid surfaces under all aqueous conditions. Noble‐metal nanoparticles obtained by citrate reduction followed by coating with thermoresponsive polymers spontaneously form a monolayer‐like structure on a wide variety of substrates in presence of sodium chloride whereas this phenomenon does not occur in salt‐free medium. Interestingly, this phenomenon occurs below the cloud point temperature of the polymers and we hypothesize that salt ion‐induced screening of electrostatic charges on the nanoparticle surface entropically favors hydrophobic association between the polymer‐coated nanoparticles and a hydrophobic substrate.     

Silica‐Coated Metal Nanoparticles

The advanced high‐quality synthesis of dense and porous silica‐coated nanostructures is enjoying ever‐increasing research interests for their important properties and diverse applications, especially for catalytic, controlled release, colorimetric diagnostics, photothermal therapy, surface enhanced Raman scattering (SERS) detection, and so forth. In this timely Focus Review, we summarize the up‐to‐date synthesis strategies, improved properties, and emerging applications of silica‐coated metal nanoparticles. In particular, the large scale synthesis of silica‐coated metal nanoparticles and the recent development of hollowed‐out silica‐coated metal nanoparticles by silica dissolution are emphasized for new and practical applications.     

Mitigation of Inflammatory Immune Responses with Hydrophilic Nanoparticles

While hydrophobic nanoparticles (NPs) have been long recognized to boost the immune activation, whether hydrophilic NPs modulate an immune system challenged by immune stimulators and how their hydrophilic properties may affect the immune response is still unclear. To answer this question, three polymers, poly(ethylene glycol) (PEG), poly(sulfobetaine) (PSB) and poly(carboxybetaine) (PCB), which are commonly considered hydrophilic, are studied in this work. For comparison, nanogels with uniform size and homogeneous surface functionalities were made from these polymers. Peripheral blood mononuclear cells (PBMCs) stimulated by lipopolysaccharide (LPS) and an LPS‐induced lung inflammation murine model were used to investigate the influence of nanogels on the immune system. Results show that the treatment of hydrophilic nanogels attenuated the immune responses elicited by LPS both in vitro and in vivo. Moreover, we found that PCB nanogels, which have the strongest hydration and the lowest non‐specific protein binding, manifested the best performance in alleviating the immune activation, followed by PSB and PEG nanogels. This reveals that the immunomodulatory effect of hydrophilic materials is closely related to their hydration characteristics and their ability to resist non‐specific binding in complex media.     

Hydrogen‐Bond‐Selective Phase Transfer of Nanoparticles across Liquid/Gel Interfaces

In the swim : Colloidal nanoparticles coated with polylactide (PLA, red) and poly(ethylene glycol) brushes (PEG, black) can transfer from organic to aqueous phases across liquid/liquid or liquid/gel interfaces during degradation of the PLA coating (see picture: first step), which is driven selectively by the hydrogen bonding of the PEG coating with the aqueous phase (second step).

     

Self‐Assembled Fluorescent Organic Nanoparticles for Live‐Cell Imaging

Fluorescent, cell‐permeable, organic nanoparticles based on self‐assembled π‐conjugated oligomers with high absorption cross‐sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge‐mediated cellular uptake by a straightforward self‐assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non‐toxic nanoparticles are suitable for both one‐ and two‐photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.     

Sodium 1‐Naphthalenesulfonate‐Functionalized Reduced Graphene Oxide Stabilizes Silver Nanoparticles with Lower Cytotoxicity and Long‐Term Antibacterial Activity

Silver nanoparticles (AgNPs) are increasingly used in daily life for their antibacterial properties, but their low stability and high cytotoxicity hamper practical applications. In this work, sodium 1‐naphthalenesulfonate‐functionalized reduced graphene oxide (NA‐rGO) was used as a substrate for AgNPs to produce a AgNP‐NA‐rGO hybrid. This hybrid showed substantially higher antibacterial activity than polyvinyl pyrrolidone(PVP)‐stabilized AgNPs, and the AgNPs on NA‐rGO were more stable than the AgNPs on PVP, resulting in long‐term antibacterial effects. More importantly, this hybrid showed excellent water solubility and low cytotoxicity, suggesting the great potential application as sprayable reduced graphene oxide based antibacterial solutions.     

Modification of porous poly(ether sulfone) membranes by low‐temperature CO2‐plasma treatment

A general method of modifying the entire cross section of porous poly(ether sulfone) membranes with a low‐temperature CO₂‐plasma treatment is reported. Both surfaces of the membranes are highly hydrophilic, with a water drop on the surface disappearing in less than 1 s, even 6 months after plasma treatment. This high hydrophilicity of both membrane surfaces results from the incorporation of hydrophilic functionalities, as evidenced by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The incorporation of these hydrophilic functionalities takes place primarily during plasma treatment, with some incorporation of atmospheric oxygen and nitrogen immediately upon exposure to air. Scanning electron microscopy shows that the membrane surface is covered by a thin, white layer that is likely the result of etching and redeposition of sputtered surface fragments. An increase in the water bubble point and glass‐transition temperature is also observed for CO₂‐plasma‐treated membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2473–2488, 2002     

Bacitracin‐Conjugated Superparamagnetic Iron Oxide Nanoparticles: Synthesis,Characterization and Antibacterial Activity

Bacitracin‐conjugated superparamagnetic iron oxide (Fe₃O₄) nanoparticles were prepared by click chemistry and their antibacterial activity was investigated. After functionalization with hydrophilic and biocompatible poly(acrylic acid), water‐soluble Fe₃O₄ nanoparticles were obtained. Propargylated Fe₃O₄ nanoparticles were then synthesized by carbodiimide reaction of propargylamine with the carboxyl groups on the surface of the iron oxide nanoparticles. By further reaction with N₃‐bacitracin in a Cu^I‐catalyzed azide–alkyne cycloaddition, the magnetic Fe₃O₄ nanoparticles were modified with the peptide bacitracin. The functionalized magnetic nanoparticles were characterized by powder X‐ray diffraction, X‐ray photoelectron spectroscopy, TEM, zeta‐potential analysis, FTIR spectroscopy and vibrating‐sample magnetometry. Cell cytotoxicity tests indicate that bacitracin‐conjugated Fe₃O₄ nanoparticles show very low cytotoxicity to human fibroblast cells, even at relatively high concentrations. In view of the antibacterial activity of bacitracin, the biofunctionalized Fe₃O₄ nanoparticles exhibit an antibacterial effect against both Gram‐positive and Gram‐negative organisms, which is even higher than that of bacitracin itself. The enhanced antibacterial activity of the magnetic nanocomposites allows the dosage and the side effects of the antibiotic to be reduced. Due to the antibacterial effect and magnetism, the bacitracin‐functionalized magnetic nanoparticles have potential application in magnetic‐targeting biomedical applications.     

Hydrophilic modification of polypropylene ultrafiltration membrane by air‐assisted polydopamine coating

Coating by a mussel inspired polydopamine (PDA) is a simple and promising strategy to modify the hydrophilicity of polymer membrane surfaces. In this work, PDA coating was used to modify polypropylene (PP) ultrafiltration hollow fiber membrane. PDA coating parameters, ie, solution concentration and coating time were varied, and the effect of those parameters on membrane morphology, porosity, water contact angle, and pure water flux was investigated. In addition, air‐assisted PDA coating process was also conducted by channelling the air through PP membrane to avoid pore blocking and prevent water flux decline. The results showed that PDA coating successfully improved the hydrophilicity of PP membrane indicated by the decrease of water contact angle from 110° to 67° after coated by 3 g/L of PDA solution for 3 hours. The addition of air permeation on membrane lumen also increased pure water flux up to 511.2 L/m².h, a 270% increase from unmodified PP membrane. It might be associated to the pore blocking prevention that has been proven by SEM image and the membrane porosity that was increased about 4%.     

Oxidase‐Like Activity of Polymer‐Coated Cerium Oxide Nanoparticles

Inorganic enzyme? Ceria nanoparticles exhibit unique oxidase‐like activity at acidic pH values. These redox catalysts can be used in immunoassays (ELISA) when modified with targeting ligands (see picture; light blue and yellow structures are nanoparticles with attached ligands). This modification allows both for binding and for detection by the catalytic oxidation of sensitive colorimetric dyes (e.g. TMB).

     

Hydrophilic Conjugated Polymers with Large Bandgaps and Deep‐Lying HOMO Levels as an Efficient Cathode Interlayer in Inverted Polymer Solar Cells

Two hydrophilic conjugated polymers, PmP‐NOH and PmP36F‐NOH, with polar diethanol­amine on the side chains and main chain structures of poly(meta‐phenylene) and poly(meta‐phenylene‐alt‐3,6‐fluorene), respectively, are successfully synthesized. The films of PmP‐NOH and PmP36F‐NOH show absorption edges at 340 and 343 nm, respectively. The calculated optical bandgaps of the two polymers are 3.65 and 3.62 eV, respectively, the largest ones so far reported for hydrophilic conjugated polymers. PmP‐NOH and PmP36F‐NOH also possess deep‐lying highest occupied molecular orbital levels of −6.19 and −6.15 eV, respectively. Inserting PmP‐NOH and PmP36F‐NOH as a cathode interlayer in inverted polymer solar cells with a PTB7/PC₇₁BM blend as the active layer, high power conversion efficiencies of 8.58% and 8.33%, respectively, are achieved, demonstrating that the two hydrophilic polymers are excellent interlayers for efficient inverted polymer solar cells.

     

Selective Electrochemical Determination of Dopamine with Molecularly Imprinted Poly(Carbazole‐co‐Aniline) Electrode Decorated with Gold Nanoparticles

Dopamine (DA) is a significant neurotransmitter in the central nervous system, coexisting with uric acid (UA) and ascorbic acid (AA). UA and AA are easily oxidizable compounds having potentials close to that of DA for electrochemical analysis, resulting in overlapping voltammetric response. In this work, a novel molecularly imprinted (MI) electrochemical sensor was proposed for selective determination of DA (in the presence of up to 80‐fold excess of UA and AA), relying on gold nanoparticles (Au_nano)‐decorated glassy carbon (GC) electrode coated with poly(carbazole (Cz)‐co‐aniline (ANI)) copolymer film incorporating DA as template (DA imprinted‐GC/P(Cz‐co‐ANI)‐Au_nano electrode, DA‐MIP‐Au_nano electrode). The DA recognizing sensor electrode showed great electroactivity for analyte oxidation in 0.2 mol L^?1 pH 7 phosphate buffer. Square wave voltammetry (SWV) was performed within 10^?4–10^?5 mol L^?1 of DA, of which the oxidation peak potential was observed at 0.16 V. The limit of detection (LOD) and limit of quantification (LOQ) were 2.0×10^?6 and 6.7×10^?6 mol L^?1, respectively. Binary and ternary synthetic mixtures of DA‐UA, DA‐AA and DA‐UA‐AA yielded excellent recoveries for DA. Additionally, DA was quantitatively recovered from a real sample of bovine serum spiked with DA, and determined in concentrated dopamine injection solution. The developed SWV method was statistically validated against a literature potentiodynamic method using a caffeic acid modified‐GC electrode.