Layer Assembly Research Articles

A pathogen imprinted hybrid polymer capacitive sensor for selective Escherichia coli detection

AbstractA versatile pathogen imprinted polymer electrochemical sensor has been developed for Escherichia coli detection. The sensor is based on layer by layer assembly of multi‐walled carbon nanotubes (CNT), nanocellulose (CNC) films, integrated with polyaniline (PANI) doped phenylboronic acid (PBA). The sensing layer is a poly(methacrylic acid) based pathogen microcontact imprinted polymer (PIP). The PIP@PBA/PANI@CNT/CNC sensor exhibits a high affinity towards E. coli in real biological matrices, while effective in discriminating E. coli amidst other bacteria. Using capacitance and impedance as transduction methods, the PIP sensor recorded a low limit of E. coli detection of 8.7 ± 0.5 cfu/ml, with a rapid response of ≤5 min.

Enhancing scratch damage resistance of PMMA via layer assembly with PVDF: Numerical modeling prediction and experimental verification

In this work, finite element modeling (FEM) and experimental test were combined to study the scratch damage behaviors of poly(methyl methacrylate) (PMMA) side of alternating multi-layered PMMA/polyvinylidene fluoride (PVDF) materials. Firstly, FEM was conducted to uncover the effect of layer thickness on critical normal load of material removal (Fcr) of the PMMA side, and the optimal thickness was determined. Then scratch tests were performed on PMMA side of the multi-layered materials, the layer thickness of which was controlled by changing layer numbers. It was found that 8-layer material possessed the highest Fcr on PMMA side (even 25% higher than pure PMMA), which was consistent with the FEM results. A more uniform deformation occurring at the surface layer was ascribed to decreasing the von Mises stress and ultimately preventing localized large deformation of PMMA, which therefore opened a new strategy to improve the scratch resistance of rigid polymers by introducing soft components.

One-dimensional Photonic Crystals Fabricated Using Stereolithographic Single Layer Assembly for the Terahertz Spectral Range

A polymer-based one-dimensional photonic crystal with a photonic bandgap in terahertz frequency range was designed and fabricated through stereolithography and was characterized using THz spectroscopy. The photonic crystal studied here consists of alternating compact and low-density layers. The compact layers were fabricated from fully polymerized polymethacrylate without any intentional internal structure. The low-density layers consist of sub-wavelength sized columns, where the volume density was selected to provide sufficient contrast between the dielectric functions of adjacent layers. The photonic crystal samples were fabricated in a single step using a commercial stereolithography system and polymethacrylate compatible with the system. Transmission spectroscopy in a range from 82 to 125 GHz was used to determine the THz spectral response of the sample. The transmission data were analyzed using stratified optical layer model calculations. A distinct photonic bandgap with a center frequency of 111 GHz was observed in the experimental transmission spectra. Bruggeman effective medium approximation was found to accurately describe the dielectric function of the low-density layers. An excellent agreement between the relevant model parameters and the corresponding design parameters was found, indicating the versatility of the approach for the fabrication of photonic crystals for the THz spectral range.

Electrodeposition Assisted Dynamic Assemblies of Chitosan/Alginate Composite Multi-Membrane

Electrodeposition of natural polymer as an effective approach to improve bioactivity of the conductive substrate has receives much attentions in medical and other applications. In this work, we developed a novel chitosan/alginate (CS/ALG) multi-membrane on titanium plate via the electrodeposition assisted dynamic assembly approach. Specifically, the electrical signal induced CS coating can serve as a versatile platform for layer by layer assemblies of ALG into the multi-membrane through strong electrostatic interaction. The prepared multi-membranes exhibit great swelling performance and excellent mechanical properties at dried states, with the tensile stress and strain values reaching to 58.2 MPa and 4.25 % for the 10 layers sample. In summary, we believe such green, low cost and rapid fabrication approach and mild processing environment would spur great potential for construction of multi-functional coating and smart drug elution system on the conductive implants.

Interlayer‐Sensitized Linear and Nonlinear Photoluminescence of Quasi‐2D Hybrid Perovskites Using Aggregation‐Induced Enhanced Emission Active Organic Cation Layers

AbstractA concept of interlayer‐sensitized photoluminescence (PL) of quasi‐2D hybrid perovskite (PVK) with a π‐conjugated optically interacting organic cation layer is introduced and demonstrated. A rod‐shaped aggregation‐induced enhanced emission (AIEE) organic cation (BPCSA+), well fitted into the lattice size of 2D PVK layers, is designed and synthesized to prolong the exciton lifetime in a condensed layer assembly in the PVK. The BPCSA+ promotes the PL of this hybrid PVK up to 10‐folds from that of a non‐π‐conjugated organic cation (OA) 2D PVK. Notably, different from PL of OA 2D PVK, the increased PL intensity of BPCSA 2D PVKs with an increase of the BPCSA ratio in the PVK indicates a critical photon‐harvesting contribution of BPCSA. The films of BPCSA 2D PVKs are incredibly stable in ambient environments for more than 4 months and even upon direct contact with water. Additionally, due to the strong two‐photon absorption property of BPCSA, the BPCSA 2D PVK displays superior emission properties upon two‐photon excitation with a short wavelength IR laser. Thus, the AIEE sensitization system for quasi‐2D PVK hybrid system can make a drastic improvement in performance as well as in the stability of the PVK emitter and PVK based nonlinear optical devices.

Composition‐dependent crystallization behavior of copolyperoxides from methyl methacrylate and 4‐vinylbenzyl stearate

AbstractTo study the composition‐dependent crystallization behavior of copolyperoxides, herein a series of copolymers were prepared by varying the ratios of methyl methacrylate (MMA) and 4‐vinylbenzyl stearate (VBS) under 100 psi oxygen pressure using AIBN as an initiator at 50°C in toluene. Both 13C NMR and electron impact mass spectroscopy (EI‐MS) approved an alternative placement of either of the monomer and peroxy (–O–O–) links throughout the polymer chain. Thermal stability of the resulting copolyperoxides was investigated by thermogravimetric analysis (TGA) and the degradation fragments have been recognized from EI‐MS study. In addition, differential scanning calorimetry (DSC) displayed an endothermic peak as well as an exotherm associated with the melting of the side chain crystalline domains and degradation of –O–O– links in the polymer main chain, respectively. Furthermore, DSC thermograms unveiled a systematic decrease of the crystalline melting temperature (Tm) with the enhancement of MMA content in the copolymers. Small angle X‐ray scattering (SAXS) revealed the existence of lamellar morphology (depends on VBS content in the copolyperoxide) in the synthesized polyperoxide materials, further supported by atomic force microscopy (AFM) analysis showing a layered fibrillar assembly with multiple heights of the lamella. The significant crystalline nature of the polyperoxides was further evidenced from the appearance of lattice fringes in the transmission electron microscope (TEM) micrographs. The crystalline morphology with birefringent texture was further evidenced from the polarized optical microscopy (POM) study. Thus, the present study reported the effective variation of crystalline behavior in copolyperoxide materials with the incorporation of MMA units in the copolyperoxide chains.

Enhanced electrochemical enantiorecognition of tryptophan enantiomers based on synergistic effect of porous β-CD-containing polymers and multiwalled carbon nanotubes

Porous β-CD-containing polymers (P-CDPs), the polymerization product of β-CD and tetrafluoroterephthalonitrile, demonstrate the high surface area and permanent porosity, which has been applied in removal of organic micropollutants and sulfides by molecular recognition. In this manuscript, an enhanced electrochemical enantioselective platform for tryptophan (Trp) enantiomers was constructed by layer by layer assembly of multiwalled carbon nanotubes (MWCNTs) and P-CDPs on the surface of GCE. The morphologies and performances of the modified electrodes were fully characterized and determined by high resolution field emission scanning electron microscopy (FESEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). And the operation parameters such as temperature and pH on the performance of electrochemical recognition were optimized. Under the optimal experimental conditions, the peak current ratio (Il-Trp/Id-Trp) could reach 2.60. The linear range for the detection of l-Trp on P-CDP/MWCNT/GCE is 8 × 10-6 M to 2 × 10-3 M and for d-Trp is 8 × 10-6 M to 4 × 10-3 M. In addition, the method could predict the ratio of l- or d-isomers in racemic mixture.

Self-stabilized fibronectin films at the air/water interface

ABSTRACTFibronectin (FN) is a mediator molecule, which can connect cell receptors to the extracellular matrix (ECM) in tissues. This function is highly desirable for biomaterial surfaces in order to support cell adhesion. Controlling the fibronectin adsorption profile on substrates is challenging because of possible conformational changes after deposition, or due to displacement by secondary proteins from the culture medium. Here, we aim to develop a method to realize self-stabilized ECM glycoprotein layers with preserved native secondary structure on substrates. Our concept is the assembly of FN layers at the air-water (A-W) interface by spreading FN solution as droplets on the interface and transfer of the layer by the Langmuir-Schäfer (LS) method onto a substrate. It is hypothesized that 2D confinement and high local concentration at A-W interface supports FN self-interlinking to form cohesive films. Rising surface pressure with time, plateauing at 10.5 mN·m-1 (after 10 hrs), indicated that FN was self-assembling at the A-W interface. In situ polarization-modulation infrared reflection absorption spectroscopy of the layer revealed that FN maintained its native anti-parallel β-sheet structure after adsorption at the A-W interface. FN self-interlinking and elasticity was shown by the increase in elastic modulus and loss modulus with time using interfacial rheology. A network-like structure of FN films formed at the A-W interface was confirmed by atomic force microscopy after LS transfer onto Si-wafer. FN films consisted of native, globular FN molecules self-stabilized by intermolecular interactions at the A-W interface. Therefore, the facile FN self-stabilized network-like films with native anti-parallel β-sheet structure produced here, could serve as stable ECM protein coatings to enhance cell attachment on in vitro cell culture substrates and planar implant materials.

Flexible molecularly imprinted electrochemical sensor for cortisol monitoring in sweat.

A selective cortisol sensor based on molecularly imprinted poly(glycidylmethacrylate-co ethylene glycol dimethacrylate) (poly(GMA-co-EGDMA)) has been demonstrated for detection of cortisol in human sweat. The non-enzymatic biomimetric flexible sweat sensor was fabricated inexpensively by layer by layer (LbL) assembly. The sensor layers comprised a stretchable polydimethylsiloxane (PDMS) base with carbon nanotubes-cellulose nanocrystals (CNC/CNT) conductive nanoporous nanofilms. The imprinted (MIP) poly(GMA-co-EGDMA) deposited on the CNC/CNT was the cortisol biomimetric receptor. Rapid in analyte response (3min), the cortisol MIP sensor demonstrated excellent performance. The sensor has a limit of detection (LOD) of 2.0ng/mL ± 0.4ng/mL, dynamic range of 10-66ng/mL, and a sensor reproducibility of 2.6% relative standard deviation (RSD). The MIP sensor also had high cortisol specificity and was inherently blind to selected interfering species including glucose, epinephrine, β-estradiol, and methoxyprogestrone. The MIP was four orders of magnitude more sensitive than its non-imprinted (NIP) counterpart. The MIP sensor remains stable over time, responding proportionately to doses of cortisol in human sweat. Graphical abstract.

Computation of effective piezoelectric properties of stratified composites and application to wave propagation analysis

AbstractA methodology for the computation of the homogenized response of stratified piezoelectric materials is proposed. The stratified composite consists of the periodic repetition of piezoelectric layers. Its effective piezoelectric properties are obtained through a homogenization approach based on the method of oscillating functions. The method can fully consider not only the elastic attributes, but also the polarizations of the materials contained within the structure's layers. As such, it proves able to obtain the homogenized electromechanical response of the stratified piezoelectric structure in the form of parametric, closed‐form expressions, which depend on the material attributes of the layers building up the repetitive unit‐cell. The applicability of the method is demonstrated for the quasi‐electrostatic wave propagation analysis of stratified composites using the nonlocal piezoelectric (NLPE) theory. A two‐layer stratified composite is employed, created as an assembly of LiNbO3 and PVDF layers. The structure's homogenized properties are used to compute the wave propagation characteristics with and without the influence of internal length parameters of the NLPE theory. The obtained results suggest that the effective properties of the stratified composite can be handily used to compute the effect of the electric field on the longitudinal and shear modes for the propagation direction of interest.

Layered Assembly of Silver Nanocubes/Polyelectrolyte/Gold Film as an Efficient Substrate for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is of great importance for the sensitive, rapid, and repeatable detection of target analytes. The electromagnetic enhancement has a major contribution to th...

Layerwise Theories of Laminated Composite Structures and Their Applications: A Review

It is very challenging to accurately analyze the displacement and stress fields in the laminated composite structures due to the transverse anisotropy and higher transverse flexibilities. The equivalent single-layer theory (EST) is first developed to simplify this complex 3D problem to a pure 2D problem based on a displacement assumption in the thickness direction. The EST gives good results for the global responses of the very thin laminates with minimum computation cost, but poor results for the local responses at the interfaces and can not presents the zig-zag distribution of in-plane displacements. The elasticity solutions based on the 3D displacement-based finite element method (FEM) can present the accurate displacement and stress fields, but requires huge computational cost. As a quasi 3D method, the layerwise theories (LWT) is more accurate than most of the ESTs, and its computational cost is less than that of the 3D-based displacement FEMs, so it is attracting more and more attention with the rapid development of computer technology. This paper presents an overall review for the LWTs of the laminated composite structures and their applications. In general, there are two basic schemes employed to establish a LWT according to the construction of the displacements fields in the thickness direction. In the first scheme, the laminated composite structures are described as an assembly of individual layers, and these individual layers are combined by the interlaminar relationships to keep the displacement continuity and stress equilibrium. All of the individual layers are simulated by using the EST. In the second scheme, the displacement and/or stress fields along the thickness direction are constructed by a 1D interpolation functions and the in-plane displacement and/or stress fields are discretized by the 2D finite elements. The review in this paper is organized by the this classification.

Sustained delivery of growth factors with high loading efficiency in a layer by layer assembly.

Layer by layer (LBL) assembly has garnered considerable interest due to its ability to generate multifunctional films with high tunability and versatility in terms of substrates and polyelectrolytes, allowing the option to use complex devices and drugs. Polyelectrolytes, such as growth factors (GFs), are essential, but costly, delicate, biological molecules that have been used in various tissue regeneration applications. For this reason, the controlled drug delivery of efficiently loaded GFs via LBL assembly (GF-LBL) can contribute to the establishment of cost-effective biologically triggered biomedical applications. We have developed an LBL method to load GFs (specifically, transforming growth factor beta 1, platelet-derived growth factor ββ, and insulin growth factor 1), with up to 90% efficiency approximately, by gas plasma surface activation and tuning the pH to increase the ionic strength of polyelectrolytes. Poly(styrenesulfonate) (PSS) and poly(ethyleneimine) (PEI) have been used to provide the initial necessary charge for multilayer build-up. Heparin and dextran sulphate have been investigated as counter polyelectrolytes to enhance the activity of GFs by protecting their ligands, where heparin resulted in the highest achievable loading efficiency for all GFs. Oxygen gas plasma and acidic pH levels also resulted in a significant increase in GF loading efficiency. The three GFs were released by diffusion and erosion in a controlled manner over lengthy time scales and the bioactivity was maintained for up to 14 days. When tested as implants in vitro, GF-LBL constructs increased fibroblast proliferation, influenced cell morphology and migration, and enhanced myofibroblast differentiation, indicating that the biological functionalities of the GFs were preserved. In conclusion, this developed LBL assembly method can provide a simple drug delivery system, which may yield more effective applications for tissue regeneration as well as biomedical sciences at large.

Improved microwave absorption performance of a multi-dimensional Fe2O3/CNTCM@CN assembly achieved by enhanced dielectric relaxation

The novel multi-dimensional hollow Fe2O3/CNTCM@CN-2 hybrid microspheres fabricated by the forcible assembly of 0D nanoparticles, 1D CNTs, and 2D N-doped carbon layers are favorable for achieving superior microwave absorption performance.

Layered double hydroxide-oriented assembly by negatively charged graphene oxide for NO2 sensing at ppb level

The ZnTi-LDHs/rGO composite is structured by combination with GO, to overcome the general stacking and low conductivity of pure ZnTi-LDHs.

Study of supercapacitive pursuance of polypyrrole/sulphonated poly (ether ether ketone) /multi walled carbon nanotubes composites for energy storage

Abstract An ample approach is adopted to fabricate an operative electrode material comprising an immaculate nanocomposite i.e. sulfonated poly (ether ether ketone) (SPEEK) and functionalized multi walled carbon nanotube (f-MWCNT) as reassuring components for polypyrrole to enhance the overall capacitance of the composited electrode. Due to effective and mutual strengthening of PPy/ SPEEK/f-MWCNT, the electrode appreciably improves its electrical response also, that sustains comfortably even with the enhanced scan rates and cyclic stability with high conductive behavior than that of their individual constituents. This research is also directed towards gaining a safe operation with minimal electrical series resistance and high charge discharge capacity. A layer by layer assembly formation by SPEEK, PPy and f-MWCNT, successfully aids this electrode, prepared for supercapacitor applications. Electrochemical properties are examined by cyclic voltammetry (CV), Nyquist plots and galvanostatic charge discharge (GCD) curves while the morphological analysis is performed by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microcopy (TEM) analyzers. Composite SPM22 prepared by combination of 98 wt% PPy/SPEEK (80:20) with 2 wt% of f-MWCNT is observed as a better electrode material for energy storage devices yielding 593 F/g specific capacitance at scan rate of 2 mV/s. An elegant course of mechanism for redox reactions is also assisting the worth of interweaved electrode material.

Chitosan-based flame retardant coatings for polyamide 66 textiles: One-pot deposition versus layer-by-layer assembly

Chitosan (CS) and phosphorylated chitosan (PCS) were deposited onto the polyamide 66 (PA66) fabric surfaces along with poly-acrylate sodium (PAS) via ‘one pot’ and layer by layer (LbL) assembly methods in preparing flame retardant coatings. Subsequently, to stabilize the deposited coatings, some of the fabric samples were treated under the UV-irradiation and additionally, a thermal treatment was also carried out for the remaining fabric samples. The LbL assembled fabrics showed a better homogeneity in the coating structure over the one pot deposited fabrics as appeared in scanning electron microscopy (SEM). Nonetheless, the LbL treated fabric sample (i.e., PA66-10BL-UV) with a higher weight gain% exhibited a greater improvement in limiting oxygen index (LOI) (i.e., 23%), and a reduced peak heat release rate (pHRR) (i.e., 25%). Yet more, only the LbL assembled and thermally cross-linked fabric sample could able to retain the flame retardant behavior in the vertical burning test even after 5 washing cycles.

Microwave-assisted preparation of ZnFe2O4-Ag/rGO nanocomposites for amplification signal detection of alpha-fetoprotein

In this study, a novel signal-amplified immunosensor was designed by using a microwave-assisted self-assembly method to synthesize ZnFe2O4-Ag/rGO nanocomposites. The conductivity of ZnFe2O4-rGO nanocomposites was significantly improved due to the effective inhibition of rGO accumulation by the insertion of ZnFe2O4 and Ag nanoparticles (NPs) into graphene sheets. Excellent sensitivity and reproducibility were achieved through the microwave-assisted preparation of ZnFe2O4-Ag/rGO nanocomposites as a substrate, with the Ag NPs enhancing the signal because of the effective conductive matrix. The layer assembly process of the immunosensor was verified by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimal conditions, the fabricated immunosensor showed good linearity over a wide concentration range from 1 pg mL−1 to 200 ng mL−1 with a low detection limit of 0.98 pg mL−1, and exhibited excellent specificity, good stability, and reproducibility. These qualities can contribute to the successful application of a label-free immunosensor in the detection of AFP in human serum.

Capillary electrophoresis-integrated immobilized enzyme microreactor with graphene oxide as support: Immobilization of negatively charged L-lactate dehydrogenase via hydrophobic interactions.

We report the first application of hydrophobic interaction between graphene oxide (GO) and negatively charged enzymes to fabricate CE-integrated immobilized enzyme microreactors (IMERs) by a simple and reliable immobilization procedure based on layer by layer assembly. L-lactate dehydrogenase (L-LDH), which is negatively charged during the enzymatic reaction, is selected as the model enzyme. Various spectroscopic techniques, including SEM, FTIR, and UV-vis are used to characterize the fabricated CE-IMERs, demonstrating the successful immobilization of enzymes on the negatively charged GO layer in the capillary surface. The IMER exhibits excellent repeatability with RSDs of inter-day and batch-to-batch less than 3.49 and 6.37%, respectively, and the activity of immobilized enzymes remains about 90% after five-day usage. The measured Km values of pyruvate and NADH of the immobilized L-LDH are in good agreement with those obtained by free enzymes. The results demonstrate that the hydrophobic interactions and/or π-π stacking is significant between the GO backbone and the aromatic residues of L-LDH and favorable to fabrication of CE-integrated IMERs. Finally, the method is successfully applied to the determination of pyruvate in beer samples.

Enhancing desalination performance of thin film composite membrane through layer by layer assembly of oppositely charged titania nanosheet

Reverse osmosis (RO) is a mature desalination technology that provides an effective solution to solve global water scarcity issues. In this study, thin film nanocomposite (TFN) membrane for RO desalination was fabricated by depositing positively charged titania nanosheet (pTNS) and negatively charged titania nanosheet (nTNS) on the surface of polyamide (PA) layer through layer by layer (LbL) assembly. The pTNS was synthesized through solid-state calcination and acid ion-exchange. Though the additional step of exfoliation, single sheet nTNS with improved hydrophilicity property was obtained. The hydration layer created on the surface of TNS-PA could hinder the direct contact of salt ions with the surface of TFN membrane, hence significantly enhance the water permeability and salt rejection. The membrane surface hydrophilicity was improved and surface roughness was decreased with the increasing number of bilayers. However, the excessive pTNS/nTNS bilayer coating has imposed additional hydraulic resistance hence resulted in the reduction of water permeability. The highest water permeability of 0.8L·m−2·h−1·bar−1 (60% improvement) was achieved with the 2 bilayers of TNS-PA TFN as compared to the pristine PA membrane. The sodium chloride (NaCl) rejection was 98.45% which was also higher than pristine membrane with rejection of 96.65%.