Preparation of PMMA/acid-modified chitosan core-shell nanoparticles and their potential as gene carriers

The core-shell nanoparticles consisting of poly(methyl methacrylate) (PMMA) cores surrounded by various acid-modified chitosan shells were synthesized using a surfactant-free emulsion copolymerization, induced by a tert-butylhydroperoxide (TBHP) solution. Methyl methacrylate (MMA) was grafted onto four acid-modified chitosans (hydrochloric, lactic, aspartic, and glutamic acids) with MMA conversions up to 64%. The prepared nanoparticles had diameter ranging from 100 to 300 nm characterized by atomic force microscopy and displayed highly positive surface charges up to +77 mV. Transmission electron microscopic images clearly revealed well-defined core-shell morphology of the nanoparticles where PMMA cores were coated with acid-modified chitosan shells. The effect of acid-modified chitosans on particle size, intensity of surface charge, morphology, and thermal stability were determined systematically. The plasmid DNA/nanoparticles complexes were investigated with ζ-potential measurement. The results suggested that these nanoparticles can effectively complex with plasmid DNAs via electrostatic interaction and could be used as gene carriers.

In situ spectroscopic ellipsometry of pH-responsive polymer brushes on gold substrates

The dynamic and reversible switching behaviour of polyelectrolyte brushes of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) toward changes of the pH value was studied by in situ VIS-spectroscopic ellipsometry (SE). For this, PDMAEMA brushes with three different molecular weights were synthesized via the “grafting from” method using surface initiated atom transfer radical polymerization. In detail, the applicability of different SE data modelling to describe the optical properties of the different brush layers in the swollen and collapsed state was investigated. Especially for the PDMAEMA brushes with a high molecular weight, an improved optical modelling of the experimental data could be achieved and revealed an exponential distribution of the PDMAEMA fraction in the brush layer.

Radical polymerization of methyl methacrylate with 2,2,3-triphenylpropanoic acid as an initiator

An unsymmetrical compound, 2,2,3-triphenylpropanoic acid (TPPA), was successfully prepared from phenyllithium, 1,1-diphenylethylene (DPE), gas carbon dioxide (CO₂), and aqueous standard solution of hydrochloric acid with LiCl deprivation. Characterization of the compound was performed by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The polymerization of methyl methacrylate (MMA) was performed in the presence of TPPA at 95 °C. The free radicals obtained were characterized by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS). Gel permeation chromatography (GPC) traces of the average molecular weight of poly(MMA) (PMMA) showed a series of translations with increasing time. The average molecular weight of PMMA indicated narrow polydispersity, and an approximately linear relationship was found between ln ([M]₀/[M]) and polymerization time.

Preparation of macroporous polyHIPE foams via radiation-induced polymerization at room temperature

PolyHIPEs are highly porous, crosslinked polymer foams typically synthesized within high internal-phase emulsions (HIPEs). Two kinds of polyHIPEs including poly(styrene-divinylbenzene) [P(St-DVB)] and poly(methyl methacrylate-divinylbenzene) [P(MMA-DVB)] foams are synthesized in this work, which are fabricated from HIPEs template via radiation-induced polymerization at room temperature. Traditional free radical polymerization initiated by potassium peroxydisulfate (KPS) at 60 °C for producing polyHIPE P(St-DVB) foams is also conducted for comparison. It is found that the amount of emulsifier can be reduced greatly in the radiation-induced polymerization of HIPEs at room temperature, compared with the traditional polymerization approach. Besides, P(MMA-DVB) PolyHIPE foams with a fine microstructure of highly interconnected pores have been successfully fabricated via radiation-induced polymerization in this work, which is usually difficult to be prepared by thermal-initiation method because of the intermediate hydrophobicity of methyl methacrylate monomer. The influences of the fraction of internal aqueous phase and the concentration of emulsifier on the structure and performance of foams are carefully explored. The structure and compression strength of the foams are characterized by scanning electron microscopy and a mechanical testing machine, respectively.

Detection of mRNA from Escherichia coli in drinking water on nanostructured polymeric surfaces using liquid crystals

In this study, we demonstrate the detection of mRNA from Escherichia coli in drinking water using thermotropic liquid crystals (LCs). After hybridization of complementary mRNA with the single-stranded DNA immobilized on a polymer substrate containing periodic sinusoidal wave patterns, the orientation of LCs transits from a uniform to a non-uniform state, thereby inducing a change in the optical response of LCs. The periodic sinusoidal features of the polymer substrate are obtained through buckling the poly-(dimethylsiloxane) slide on a cylindrical surface, followed by replicating the associated relief structures on a poly-(urethaneacrylate) surface, where a film of gold was deposited. Then, thiol-modified single-stranded DNA was functionalized on the gold film as an mRNA receptor. The formation of mRNA–single-stranded DNA complex, which covers the sinusoidal nanostructures on the surface, induces the orientational transition of LCs. This result indicates that LCs can be used to report the specific hybridization of mRNA with single-stranded DNA, which holds promise for the sensitive and label-free detection of viable bacterial pathogens in drinking water.

Synthesis and properties of polyfluoro(silyl)acetylene nanoparticles by reaction of fluoro(silyl)acetylenes with triethylamine

Fluoro(silyl)acetylenes, which were prepared by reaction of 1,1-difluoroethylene with silyl chlorides, reacted with triethylamine to give dark-brown colored polyfluoro(silyl)acetylene powders in excellent to moderate isolated yields. In contrast, the corresponding nonfluorinated acetylene was unable to react with triethylamine at all to afford poly(silyl)acetylene under similar conditions. Polyfluoro(silyl)acetylenes thus obtained were nanometer size-controlled cubic fine particles with a good dispersibility and stability in a variety of solvents. These polyfluoro(silyl)acetylene nanoparticles exhibited clear absorption and emission spectra related to the conjugated units in polymer main chain. Furthermore, these polyfluoro(silyl)acetylene nanoparticles were applied to the surface modification of poly(methyl methacrylate) [PMMA] film to exhibit a higher oleophobicity imparted by fluorine on their surface, compared to that on the reverse side.

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Efficient sample proteolysis based on a microchip containing a glass fiber core with immobilized trypsin

Trypsin was immobilized on cellulose-coated glass fibers via a condensation reaction between the aldehyde groups of the oxidized cellulose and the primary amino groups of trypsin. A piece of the modified fiber was inserted into the main channel of a poly(methyl methacrylate) microchip to form a microfluidic proteolytic bioreactor. Scanning electron microscopy of the cross section of the fiber revealed a rough film on the surface of the fiber glass. The performance of the bioreactor was demonstrated by the tryptic digestion of hemoglobin and cytochrome c, where the time for digestion was reduced to <10?s. The digests were identified by MALDI-TOF-MS to obtain peptide mass fingerprint spectra. The results indicated that the digestion in the microfluidic bioreactor is comparable to that of a 12-h solution tryptic digest and thus provides a promising platform for the high throughput identification of proteins.

Iron oxide film growth under ultrathin polysiloxane networks

This study focuses on the preparation and characterization of magnetic switchable thin iron oxide–polymer films. In a series of experiments, the formation and growth of iron oxide under ultrathin polysiloxane layers was controlled by changing the concentration of iron ions in the aqueous subphase or by varying the residence time of ammonia in the gas phase above the liquid sample. The growth of the combined film structures is studied in situ by interfacial rheology, optical microscopy, and x-ray scattering experiments and ex situ by scanning electron microscopy. Different stages of iron oxide aggregation, from a very thin layer of amorphous iron oxide with thickness of a few nanometers up to micrometer thick coatings of crystalline maghemite (γ-Fe₂O₃) were investigated. The specific interactions between the inorganic iron oxide and the polymer membranes cause the creation of new composite materials which are sensitive to magnetic forces.

Correlation between wetting properties and electrical performance of solution processed PEDOT:PSS/CNT nano-composite thin films

Nano-composite thin films of poly(3,4-ethylenedioxythiophene) poly(styrene-sulfonate) (PEDOT:PSS) with different loading concentrations of multi-walled carbon nanotubes (MWCNT) were deposited on glass substrates using inkjet printing and spin coating techniques. The surface energy of the substrate was modified using an oxygen plasma to achieve different degrees of wetting by the composite solution. We show that the electrical properties strongly depend on the wetting of the substrate and by controlling the wettability, the conductivity of the nano-composite samples can be improved. Based on polymer conductivity, the electrical conductivity of the composite film can be improved or degraded by orders of magnitude with the incorporation of the same concentration of MWCNT. Moreover, electrical measurements show strong correlation between the conductivity of the carbon nanotube network and the resulting nano-composite films. The dependence of electrical properties on the wettability and the conductivity of the composite components could explain the diversity in the electrical behaviour reported in the literature for PEDOT:PSS/MWCNT nano-composite thin films.

Facile fabrication of snowman-like Janus particles with asymmetric fluorescent properties via seeded emulsion polymerization

This paper presents a facile method for the preparation of snowman-like Janus particles (SJP) with asymmetric fluorescent property via seeded emulsion polymerization, in which in situ formed raspberry-like cadmium sulfide/poly(styrene–divinylbenzene–acrylic acid) nanocomposite particles (RNP) were used as the seeds. The as-prepared RNP and SJP have been thoroughly characterized by transmission electron microscopy, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray powder diffraction, Fourier transform infrared, ultraviolet visible, and photoluminescent spectrometry. It is found that the size ratio of the polymer bulge/inorganic seed part could be continuously tuned as well as the composition of polymer bulges by changing the composition of monomer mixtures and monomer/seed weight ratio. The obtained Janus particles possess amphiphilic properties which can be further used as solid surfactants to stabilize W/O emulsions and successively to construct hierarchical structured materials. Meanwhile, their asymmetric fluorescent properties may be exploited to detect their assembled situation and orientation at the oil–water interface of emulsions as well as at the surface of hierarchical structured materials.

Influence of second virial coefficient and persistence length on dilute solution polymer conformation

The effect of different types of short- and long-range intrachain interactions along the polymeric backbone on the persistence length of a polymer, as well as on other properties such as solvation (characterized by the second virial coefficient), dilute solution conformation, specific refractive index increment, and intrinsic viscosity, were studied using multi-detector size-exclusion chromatography and off-line techniques. The polymers in this study, namely, polystyrene (PS), poly(vinyl chloride) (PVC), and poly(p-vinylbenzyl chloride) (PpVBC), were chosen based on intrachain interactions specific to each, intrachain repulsion in PVC, attraction in PS, and hindered attraction in PpVBC, and also based on a coincidence in molar mass averages and distributions between the polymers. The latter allowed polymeric properties of the three polymers to be compared to each other at the same molar mass and/or degree of polymerization. From the comparisons emerged the effects of intrachain repulsion between consecutive monomers and of the second virial coefficient on chain stiffness and solvation. The increase in the second virial coefficient corresponded to an increase in both polymer solvation and rigidity, while increased intrachain repulsion between consecutive monomers increased polymer solvation while decreasing chain rigidity.

Preparation of a nanocomposite film from poly(diallydimethyl ammonium chloride) and gold nanoparticles by in-situ electrochemical reduction, and its application to SERS spectroscopy and sensing of ascorbic acid

A nanocomposite film is described that is composed of alternating layers of poly(diallydimethyl ammonium chloride) and gold nanoparticles that interact through electrostatic forces. The films of varying thickness were prepared by the layer-by-layer technique, and Au-NPs were generated by electrochemical reduction of hexachloroauric acid. The composite films were characterized by UV?Cvis spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Most nanocomposite films exhibit linear, uniform, and regular layer-by-layer growth during the process of formation. The films exhibit unique performance in terms of surface enhanced Raman scattering and electrocatalytic activitiy towards the oxidation of ascorbic acid.

Electrochemical sensor for nitrobenzene based on carbon paste electrode modified with a poly(3,4-ethylenedioxythiophene) and carbon nanotube nanocomposite

A sensitive and selective electrochemical sensor for the determination of nitrobenzene (NB) was developed based on a carbon paste electrode (CPE) modified with a nanocomposite prepared from the conducting polymer poly(3,4-ethylenedioxythiophene) and carbon nanotubes. The modified CPE exhibits good conductivity, a large surface area, and excellent catalytic activity towards the electrochemical reduction of NB. Under optimal conditions, the modified CPE is capable of detecting NB in the 0.25 to 43 μM concentration range and with a detection limit at 83 nM. Moreover, the sensor is highly stable and reusable, and free of interferences by other commonly present nitro compounds. It was used to determine NB in wastewater samples.

The complete replacement of antibodies by protein-imprinted poly(ethylene-co-vinyl alcohol) in sandwich fluoroimmunoassays

The replacement of antibodies by molecularly imprinted polymers (MIPs) has been investigated for many decades. However, indirect protocols (including natural primary and secondary antibodies) are still utilized to evaluate the ability of MIP thin films to recognize target molecules. MIPs can be prepared as either a thin film or as particles, and cavities that are complementary to the template can be generated on their surfaces. We have prepared thin film MIPs and particle MIPs prepared by solvent evaporation and phase inversion, respectively, from solutions of poly(ethylene-co-vinyl alcohol) (pEVAL) in the presence of the target analytes amylase, lysozyme, and lipase. These were first adsorbed on MIP thin films and by MIP particles that contain fluorescent quantum dots. Sandwich fluoroimmunoassays were then conducted to quantify them in MIP-coated 96-well microplates. The method was applied to determine amylase in saliva, and results were compared with a commercial analytical system.

pH/Thermosensitive Hydrogels Formed at Low pH by a PMMA‐PAA‐P2VP‐PAA‐PMMA Pentablock Terpolymer

A poly(methyl methacrylate)‐block‐poly(acrylic acid)‐block‐poly(2‐vinyl pyridine)‐block‐poly(acrylic acid)‐block‐poly(methyl methacrylate) (PMMA‐PAA‐P2VP‐PAA‐PMMA), pentablock terpolymer has been synthesized by anionic polymerization with sequential addition of monomers and studied in aqueous media at low pH. The system exhibits combined properties and adopts the behavior of ‘telechelic’ polyelectrolytes and that of double hydrophilic polyampholytes. This complex behavior leads to the pentablock terpolymer forming a pH and temperature sensitive reversible hydrogel at very low polymer concentration.

     

Graft copolymers via combination of cationic polymerization and atom transfer radical polymerization and their phase separation into spherical/worm-like nanostructures

Poly(p-chloromethyl styrene)-graft-poly(methyl methacrylate) (PCMS-g-PMMA) and poly(p-chloromethyl styrene)-graft-poly(benzyl methacrylate) (PCMS-g-PBzMA) graft copolymers with asymmetric branches are synthesized via the combination of cationic polymerization and atom transfer radical polymerization (ATRP). The process involves first, the preparation of poly(p-chloromethyl styrene) (PCMS-CH₂Cl) macroinitiator without any cross-linking or side reactions through pendant benzyl chloride (?CH₂Cl) functionality by cationic polymerization using a simple FeCl₃-based initiating system at 25 °C. The as-synthesized PCMS-CH₂Cl, without any transformation, is then used as the macroinitiator to graft PMMA and PBzMA branches by ATRP to produce PCMS-g-PMMA and PCMS-g-PBzMA graft copolymers of varying compositions with controlled molecular weight and moderately narrow polydispersities (M _w/M _n?≤?1.32). The resulting PCMS₂₁ -g-PMMA₂₃₂ graft copolymer in thin film form phase separates into spherical morphology with an average diameter of 170?±?72 nm. Whereas the PCMS₂₁ -g-PBzMA₁₅₆ graft copolymer gives worm-like nanostructures with an average length of 94 nm and width of 31 nm due to phase separation as visualized through atomic force microscopy. On the other hand, the phase-separated morphology is not very well-defined for other graft copolymers (PCMS₁₁₃ -g-PMMA₂₂₇ and PCMS₁₁₃ -g-PBzMA₁₅₄) thin films containing longer PCMS chains. This approach represents a rapid and convenient route to prepare unique spherical/worm-like polymer nanostructures. Figure

Well-defined poly(p-chloromethyl styrene)-graft-poly(methyl methacrylate) (PCMS-g-PMMA) and poly(p-chloromethyl styrene)-graft-poly(benzyl methacrylate) (PCMS-g-PBzMA) graft copolymers with asymmetric branches are synthesized by the combination of living cationic polymerization and atom transfer radical polymerization (ATRP). The resulting PCMS₂₁ -g-PMMA₂₃₂ and PCMS₂₁ -g-PBzMA₁₅₆ graft copolymers phase separate into nanostructured spherical and worm-like morphologies, respectively, in thin film form. The phase-separated morphology is not very well-defined for graft copolymers (PCMS₁₁₃ -g-PMMA₂₂₇ and PCMS₁₁₃ -g-PBzMA₁₅₄) thin films containing longer PCMS chains.     

A surface plasmon resonance study on the optical properties of gold nanoparticles on thin gold films

We report on an investigation of the optical properties of gold nanoparticles assembled as thin films of different thickness. The nanoparticles were linked to the surface of a gold chip by dithiol reagents and studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy. There is good correlation between the experimental findings and theoretical simulation, and the respective data reveal the presence of ordered nanostructures in the assemblies. The shift in the SPR angle is linearly dependent on the particle size and the ratio of the different particles. SPR spectroscopy also reveals important information in terms of the optical constants of such films. This shall be further applied to in-situ quality control in the fabrication of optoelectronic, solar cell and semiconductor devices.

Hydrophilic modification of poly(vinylidene fluoride) (PVDF) by in situ polymerization of methyl methacrylate (MMA) monomer

The hydrophilicity of poly(vinylidene fluoride) (PVDF) was first improved by in situ polymerization of polar monomer in PVDF solution. Methyl methacrylate was adopted as the reaction monomer, and the polymerization occurred in a solution of PVDF in N,N-dimethylformamide. PVDF/poly(methyl methacrylate) (PMMA) blend was obtained after in situ polymerization. The relative hydrophilicity of the in situ blend was characterized by contact angle measurement. At the same time, the hydrophilicity of the PVDF/PMMA blends prepared by solution blending was compared with that of the in situ blend. The contact angle measurements indicated that in situ polymerization has a stronger modifying effect on the hydrophilicity of PVDF than solution blending.     

Visualization of red-ox proteins on the gold surface using enzymatic polypyrrole formation

We describe a new method for the visualization of the activity of red-ox proteins on a gold interface. Glucose oxidase was selected as a model system. Surfaces were modified by adhesion of glucose oxidase on (a) electrochemically cleaned gold; (b) gold films modified with gold nanoparticles, (c) a gold surface modified with self-assembled monolayer, and (d) covalent immobilization of protein on the gold surface modified with a self-assembled monolayer. The simple optical method for the visualization of enzyme on the surfaces is based on the enzymatic formation of polypyrrole. The activity of the enzyme was quantified via enzymatic formation of polypyrrole, which was detected and investigated by quartz microbalance and amperometric techniques. The experimental data suggest that the enzymatic formation of the polymer may serve as a method to indicate the adhesion of active redox enzyme on such surfaces.