Chitosan/Sodium Alginate Multilayer pH-Sensitive Films Based on Layer-by-Layer Self-Assembly for Intelligent Packaging

The abuse of plastic food packaging has brought about severe white pollution issues around the world.Developing green and sustainable biomass packaging is an effective way to solve this problem.Hence,a chitosan/sodium alginate-based multilayer film is fabricated via a layer-by-layer(LBL)self-assembly method.With the help of superior interaction between the layers,the multilayer film possesses excellent mechanical properties(with a tensile strength of 50 MPa).Besides,the film displays outstanding water retention property(blocking moisture of 97.56%)and ultraviolet blocking property.Anthocyanin is introduced into the film to detect the food quality since it is one natural plant polyphenol that is sensitive to the pH changes ranging from 1 to 13 in food when spoilage occurs.It is noted that the film is also bacteriostatic which is desired for food packaging.This study describes a simple technique for the development of advanced multifunctional and fully biodegradable food packaging film and it is a sustainable alternative to plastic packaging.

Enhanced performance of a solar cell based on a layer-by-layer self-assembled luminescence down-shifting layer of core–shell quantum dots

In this paper, core–shell quantum dots(QDs) with two polar surface functional groups(ZnSe/ZnS–COOH QDs and ZnSe/ZnS–NH_2 QDs) are synthesized in an aqueous phase. Photoluminescence(PL) and absorption spectra clearly indicate luminescence down-shifting(LDS) properties. On the basis of QDs, surface functional group multilayer LDS films(MLDSs) are fabricated through an electrostatic layer-by-layer(LBL) self-assembly method. The PL intensity increases linearly with the number of bilayers, showing a regular and uniform film growth. When the M-LDS is placed on the surface of a Si-based solar cell as an optical conversion layer for the first time, the external quantum efficiency(EQE) and shortcircuit current density(Jsc) notably increases for the LDS process. The EQE response improves in a wavelength region extending from the UV region to the blue region, and its maximum increase reaches more than 15% between 350 nm and 460 nm.

Layer-by-layer electrostatic selfassembly of anionic and cationic carbon nanotubes

The layer-by-layer(LBL) self assembly of anionic and cationic multi-walled carbon nanotubes(MWNTs) through electrostatic interaction has been carried out to fabricate all-MWNT multilayer films.The alternate uniform assembly of anionic and cationic MWNTs was investigated by UV-vis spectroscopy.Scanning electron microscopy(SEM) images displayed the growth of the MWNT films.

Layer-by-layer self-assembly and clinical application in orthopedics

Orthopedic implants for the treatment of bone defects from various causes have been challenged by insufficient osseointegration,bacterial infection,oxidative stress,immune rejection,and insufficient individualized treatment.These challenges not only impact treatment outcomes but also severely impact patients’daily lives.Layer-by-Layer(LbL)serves as a simple surface coating technique,in simple terms,to functionalize implants by sequentially adsorbing oppositely charged materials onto a substrate.In orthopaedics,LbL self-assembly technology solves some of the challenges by loading various drugs or biological agents on the implant surface and controlling their release precisely to the site of bone defects in a personalized way.This review will introduce the basic principle and the development of LbL in orthopaedics,review and analyze the chemical strategy of LbL in the preparation of bone implants to ensure the stability of the implant,and introduce the use of LbL bone implants in orthopaedics in recent years.The application of LbL includes the realization of programmed drug delivery and sustained release,thereby promoting osseointegration and the formation of new blood vessels,antibacterial,antioxidant,etc.This review focuses on the LbL technology,involving the technology selection for the preparation of bone implants,the chemical strategies of the stability guarantee of LbL implants,the pharmacological properties,loading and release mechanisms of loaded drugs,and the molecular mechanisms of osteogenesis and angiogenesis.The aim of this review is to provide an overview of current research advances,and a prospect in this field was also described.

Mg-Zn-Y-Nd coated with citric acid and dopamine by layer-by-layer self-assembly to improve surface biocompatibility

Magnesium alloy has been generally accepted as an important biodegradable material on cardiovascular stent development for a long time. However, its limited biocompatibility, especially delayed endothelialization process restricts its further application. In this contribution, we modified the Mg-Zn-Y-Nd alloy surface with citric acid and dopamine via a layer-by-layer self-assembly assay, aiming at improving the biocompatibility of the magnesium alloy. The citric acid/dopamine(CA/PDA) layer exhibited a remarkable suppression of platelet activation/aggregation and thrombosis under 15 dyn/cm2 blood flowing. Inhibition on vascular smooth muscle cells growth and macrophages attachment/activation were also observed on this layer. In particular, the CA/PDA layer presented a promoted property for the vascular endothelial cells growth and spreading compared with the bare magnesium alloy, suggesting the pro-endotelialized function. In conclusion, this research may support potential application on surface modification of magnesium alloy based cardiovascular stents for better biocompatibility.

Fabrication of PTFE/Nomex fabric/phenolic composites using a layer-by-layer self-assembly method for tribology field application

Fabric composites are widely applied as self-lubricating liner for radial spherical plain bearings owing to their excellent mechanical and tribological properties.Nevertheless,the poor interfacial strength between fibers and the resin matrix limits the performance of composites utilized as tribomaterials.To overcome this drawback,a mild layer-by-layer(LbL)self-assembly method was successfully used to construct hybrid fabric composites in the present work.In addition,this investigation addressed the effect of self-assembly cycles on the friction and wear behaviors of hybrid fabric composites under dry sliding condition.The results demonstrate that fabric composites with three or more self-assembly cycles have significantly enhanced surface activities and anti-wear performances.The results obtained in this work can provide guidance in the preparation of self-lubricating liner composites and highlight how the LbL self-assembly techniques could influence the properties of hybrid fabric composites.

Preparation of Au/Ag Multilayers via Layer-by-Layer Self-assembly in Spherical Polyelectrolyte Brushes and Their Catalytic Activity

Spherical polyelectrolyte brushes （SPBs） consisting of polystyrene （PS） core and poly（2-aminoethyl methacrylate hydrochloride） （PAEMH） shell were prepared by photo-emulsion polymerization. Au nanoparticles （Au-NPs） with controlled size and size distribution were synthesized in situ using SPBs as nanoreactors. Via layer-by-layer deposition technique on the surface of SPBs, nano-composite particles with Au/Ag-NPs bilayer and Au/Ag/Au-NPs trilayer were prepared. The structures of the as-prepared Au/Ag multilayer SPBs were characterized by UV-Vis spectroscopy, TEM, ICP-AES and DLS. The charge reversal of the nano-composite particles observed by zeta potential confirmed the success of layer-by-layer assembly. The Au/Ag-NPs bilayer nano-composite particles showed high catalytic efficiency with an apparent activation energy of about 41.2 kJ/mol in the reduction reaction of 4-nitrophenol to 4-aminophenol in the existence of sodium borohydride monitored. The catalytic activity ofAu/Ag-NPs multilayer SPBs close to that of Au-NPs SPBs and much higher than that of Ag-NPs SPBs reveals its potential applications in cost-effective catalysts with high-performance.

Sensing Escherichia coli O157:H7 via frequency shift through a self-assembled monolayer based QCM immunosensor

By means of the specific immuno-recognition and ultra-sensitive mass detection, a quartz crystal microbalance (QCM) biosensor for Escherichia coli O157:H7 detection was developed in this work. As a suitable surfactant, 16-mercaptohexadecanoic acid (MHDA) was introduced onto the Au surface of QCM, and then self-assembled with N-hydroxysuccinimide (NHS) raster as a reactive intermediate to provide an active interface for the specific antibody immobilization. The binding of target bacteria with the immobilized antibodies decreased the sensor’s resonant frequency, and the frequency shift was correlated to the bacterial concentration. The stepwise assembly of the immunosensor was characterized by means of the electrochemical techniques. Using the immersion-dry-immersion procedure, this QCM biosensor could detect 2.0×102 colony forming units (CFU)/ml E. coli O157:H7. In order to reduce the fabrication time, a polyelectrolyte layer-by-layer self-assembly (LBL-SA) method was adopted for fast construction. Finally, the reproducibility of this biosensor was discussed.

Layer-by-layer stacked graphene nanocoatings by Marangoni self-assembly for corrosion protection of stainless steel

Graphene nanosheets are widely used in anti-corrosion polymeric coating as filler,owing to the excellent electrochemical inertness and barrier property.However,as the arrangement of graphene nanosheets is difficult to form a perfect layered structure,polymeric coating with graphene nanosheets usually needs micron-scale thickness to ensure the enhancement of corrosion protection.In this work,layer-by-layer stacked graphene nanocoatings were fabricated on stainless steel by self-assembly based on Marangoni effect.The anti-corrosion property of graphene coatings were studied through Tafel polarization curves,electrochemical impedance spectroscopy and accelerated corrosion test with extra applied voltage.The self corrosion current density of optimized three-layered graphene coated sample was one quarter of that of bare stainless steel.And the self corrosion potential of optimized sample is increased to-0.045 V.According to the results,graphene nanocoatings composed of layered nanosheets exhibits good anticorrosion property.Besides,the self-assembly method provide a promising approach to make layeredstructure coating for other researches about 2 D material nanosheets.

Layer-by-layer Multilayer Films Self-assembled from a Rare-earth-containing Poly-oxometalate Na_9[Eu(W_5O_(18))_2] and Poly(allylamine hydrochloride) and Their Photoluminescent Properties

Ultrathin multilayer films of a rare-earth-containing polyoxo-metalateNa_9[Eu(W_5O_(18))_] (EW) and poly ( allylamine hydrochloride) (PAH) have been prepared bylayer-by-layer self-assembly from dilute aqueous solutions. The fabrication process of the EW/PAHmultilayer films was followed by UV-vis spec-troscopy and ellipsometry, which show that thedeposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayerthickness of ca. 2.1 nm was determined by ellipsometry. In addition, the scanning electronmicroscopy (SEM) image of the EW/PAH film indicates that the film surface is relatively uniform andsmooth. The photolumi-nescent properties of these films were also investigated by fluorescencespectroscopy.

光敏自组装多层膜用于向列型液晶光控取向的研究

合成了含有光敏基团、双端为季铵阳离子的有机铵盐 .将这种季铵盐与聚乙烯基苯磺酸钠用 LBL(Layer-by-layer)方法组装成多层分子沉积膜 ,紫外光谱证明 ,这个过程为逐层、均匀沉积过程 .在偏振紫外光照射下 ,多层膜中和光矢量方向匹配的光敏基团发生 [2 +2 ]环加成反应 ,形成表面张力各向异性膜 .用该薄膜作向列相液晶的取向膜制成反平行液晶器件 ,在偏光显微镜下观察 ,发现取得均一、稳定的取向效果 .

共价反应型多层有机-无机复合膜组装及其渗透汽化性能

对共价反应型多层有机-无机复合膜组装及其渗透汽化性能进行了研究.采用经硅烷偶联剂改性后的管式陶瓷膜作为基膜,通过动态层层吸附自组装(layer-by-layer,LbL)技术在管式陶瓷膜内表面分别组装聚丙烯酸(poly acrylic acid,PAA)/聚乙烯醇(poly vinyl alcohol,PVA)/戊二醛(glutaraldehyde,GA),再通过热交联引发层间反应,生成共价键,形成稳定性较强的多层复合分离膜,并将其用于渗透汽化领域.考察了组装层数、复合时间、交联温度和PVA相对分子质量等条件对复合膜性能的影响.结果表明:当组装层数为5层、进料液温度为75℃时,有机-无机复合膜对95%的乙醇/水体系,其透过液水的质量分数为99.5%,渗透通量可达102 g/(m2·h).

Study of enzyme biosensor based on carbon nanotubes modified electrode for detection of pesticides residue

The paper describes a controllable layer-by-layer （LBL） self-assembly modification technique of multi-walled carbon nanotubes （MWNTs） and poly（diallyldimethylammonium chloride） （PDDA） towards glassy carbon electrode （GCE）, Acetylcholinesterase （ACHE） was immobilized directly to the modified GCE by LBL self-assembly method, the activity value of AChE was detected by using i-t technique based on the modified Ellman method. Then the composition of carbaryl were detected by the enzyme electrode with 0.01U activity value and the detection limit of carbaryl is 10^- 12 g L ^-1 so the enzyme biosensor showed good properties for pesticides residue detection.

Delivery of surface-mediated non-viral gene nanoparticles from ultrathin layer-by-layer multilayers

An efficient and safe gene delivery system remains a challenge in the development of gene therapy.Polycation-based gene nanoparticles are a typical non-viral gene delivery system,which are able to transfect cells in vitro and in vivo.This paper reported a facile method for constructing biodegradable multilayers via layer-by-layer self-assembly,in which the polycation-based gene nanoparticles were loaded.Through this surface-mediated delivery system,adherent cells on the multilayer could be transfected in situ.Gene nanoparticles-loaded multilayers transfect cells with higher efficiency than naked DNA-loaded multilayers because of the complex configuration of the DNA.DNA nanoparticles/PGA multilayers constructed on the scaffold surface could also realize in situ transfection on the adherent cells.The well-structured,easy-processed multilayers may provide a novel approach to precisely controlled delivery of gene nanoparticles,which may have potential applications for gene therapy in tissue engineering and medical implants.

Layer-by-layer slot-die coated high-efficiency organic solar cells processed using twin boiling point solvents under ambient condition

Layer-by-layer (LbL) strategy has been developed to form bulk heterojunction (BHJ) structure for processing efficient organic solar cells (OSCs). Herein, LbL slot-die coating with twin boiling point solvents (TBPS) strategy was developed to fabricate highly efficient OSCs, which matches with large-scale, high throughput roll-to-roll (R2R) industrialized mass process. The TBPS strategy could produce high-quality thin film without any additive, leading to the optimized vertical phase separation with interpenetrating nanostructures, as well as the enhanced charge transport and extraction. Thus, the power conversion efficiency up to 14.42% was achieved for [(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo [1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)]:2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4″,5″]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene)) bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (PM6:Y6) OSCs fabricated via sequentially LbL slot-die coating using the TBPS strategy under ambient condition. The research provides a potential route for industrialized production of high-efficiency and large-area OSC devices.

Determination of carcinoembryonic antigen using a novel amperometric enzyme-electrode based on layer-by-layer assembly of gold nanoparticles and thionine

Electrochemical sensing of carcinoembryonic antigen(CEA)on a gold electrode modified by the se- quential incorporation of the mediator,thionine(Thi),and gold nanoparticles(nano-Au),through co- valent linkage and electrostatic interactions onto a self-assembled monolayer configuration is de- scribed in this paper.The enzyme,horseradish peroxidase(HRP),was employed to block the possible remaining active sites of the nano-Au monolayer,avoid the non-specific adsorption,instead of bovine serum albumin(BSA),and amplify the response of the antigen-antibody reaction.Electrochemical ex- periments indicated highly efficient electron transfer by the imbedded Thi mediator and adsorbed nano-Au.The HRP kept its activity after immobilization,and the studied electrode showed sensitive response to CEA and high stability during a long period of storage.The working range for the system was 2.5 to 80.0 ng/mL with a detection limit of 0.90 ng/mL.The model membrane system in this work is a potential biosensor for mimicking the other immunosensor and enzyme sensor.

PREPARATION OF POLYELECTROLYTE MULTILAYER COATED MICROBUBBLES FOR USE AS ULTRASOUND CONTRAST AGENT

Objeelive To prepare and characterize polyelectrolyte multilayer film coated microbubbles for use as ultrasound contrast agent （UCA） and evaluate its effects in ultrasonic imaging on normal rabbit＇s fiver parenchyma. Methods Perfluorocarbon （PFC）-containing microbubbles （ST68-PFC） were prepared by sonication based on suffactant （ Span 60 and Tween 80）. Subsequently, the resulting ST68-PFC microbubbles were coated using oppositely charged polyelectrolytes by microbubble-templated layer-by-layer self-assembly technique via electrostatic interaction. The enhancement effects in ultrasonic imaging on normal rabbit＇s liver parenchyma were assessed. Results The obtained microbubbles exhibited a narrow size distribution. The polyelectrolytes were successfully assembled onto the surface of ST68-PFC microbubbles. In vivo experiment showed that polyelectrolyte multilayer film coated UCA effectively enhanced the imaging of rabbit＇s liver parenchyma. Conclusions The novel microbubbles UCA coated with polyelectrolyte multilayer, when enabled more function, has no obvious difference in enhancement effects compared with the pre-modified microbubbles. The polymers with chemically active groups （ such as amino group and carboxyl group） can be used as the outermost layer for attachment of targeting ligands onto microbubbles, allowing selective targeting of the microbubbles to combine with desired sites.

Assembly of layer-by-layer films of superoxide dismutase and gold nanorods:A third generation biosensor for superoxide anion

Based on the layer-by-layer self-assembly of positively charged cetyltrimethylammonium bromide （CTAB） wrapped gold na- norods （AuNRs） and negatively charged superoxide dismutase （SOD） from their aqueous solutions on cysteine modified gold electrode （Cys/Au）, a third generation electrochemical biosensor （（SOD/AuNRs）2/Cys/Au） for superoxide anion （02＂-） was developed. The two layers assembly of SOD/AuNRs can significantly enhance the direct electron transfer between SOD and the electrode. The functional enzymatic activities of the SOD offer an electrochemical approach to the determination of 02＂-. In the reductive regions, the proposed sensor exhibits excellent analytical performances, such as wide linear range （200 nM to 0.2 mM O2-）, low detection limit （100 nM O2-）, high sensitivity （22.11 nA cm-2 μM-1）, short response time （less than 5 s）, good stability and reproducibility, while no obvious interferences are caused by commonly met interfering species including hydrogen peroxide （H202）, uric acid （UA） and ascorbic acid （AA）.

Fabrication of Covalently Linked PAH/PVS Layer-by-layer Assembled Multilayers via a Post-photochemical Cross-linking Strategy

A post-photochemical cross-linking strategy was successfully demonstrated to enhance the stability of polyelectrolyte poly（allylamine hydrochloride）（PAH）/poly（vinylsulfonic acid sodium salt）（PVS） multilayers. Con- ventional polyelectrolyte multilayers of PAH/PVS are usually fabricated through electrostatic layer-by-layer（LbL） assembly, resulting in poor stability, especially in basic solutions, which leads to the urgent demand for converting weak electrostatic interactions into covalent bonds to enhance the stability of the multilayers. This stability problem has been ultimately addressed by post-infiltrating a photosensitive cross-linking agent, 4,4＇-diazostilbene-2,2＇- disulfonie acid disodium salt（DAS）, into the LbL assembled films to initiate the photochemical reaction to cross-link the multilayers. The obviously improved stability of the photo-cross-linked multilayers was demonstrated through experiments with basic solution treatments. Compared to the complete decomposition of uncross-linked multilayers in basic solution, over 74.4% of the covalently cross-linked multilayers were retained under the same conditions, even after a longer duration of basic solution treatment.

LIGHT-SCATTERING STUDY OF POLYELECTROLYTE HOLLOW CAPSULES

Silver halide (AgX) microcrystal was used as template to synthesize hollow polyelectrolyte capsules. These hollow capsules were characterized by laser light scattering (LLS) used to measure the size of the capsules in solution. The ratio of hydrodynamic radius (R h ) from dynamic LLS to the radius of gyration (Rg) from static LLS is almost unity, revealing that the entities are hollow in solution. The results suggest that the LLS method can be regarded as a good complement to the confocal laser scanning microscopy (CLSM) method for the characterization of small hollow capsules, and it possesses the advantage of not needing fluorescence labeling.