Assembly of electroactive layer-by-layer films of myoglobin and small-molecular phytic acid

In the present work, small-molecular phytic acid (PA) with its unique structure was successfully assembled with myoglobin (Mb) into {PA/Mb}_n layer-by-layer films on solid surfaces. Quartz crystal microbalance (QCM) and cyclic voltammetry (CV) were used to monitor or confirm the assembly process. IR and UV–vis spectroscopy indicate that the Mb in {PA/Mb}_n films retains its near native structure. The direct electrochemistry of Mb was realized in this new kind of films at pyrolytic graphite (PG) electrodes, and was used to electrocatalyze the reduction of various substrates. The interaction between PA and Mb under different pH conditions was also explored. Not only the oppositely charged PA and Mb at pH 5.0, but also the likely charged PA and Mb at pH 9.0, could be assembled into {PA/Mb}_n films. This work provides a novel avenue to fabricate protein multilayer films with small molecules and realizes the direct electrochemistry of redox proteins in the films.     

Fabrication of electroactive layer-by-layer films of myoglobin with gold nanoparticles of different sizes

Alternate adsorption of oppositely charged myoglobin (Mb) and gold nanoparticles with different sizes were used to assemble {Au/Mb}n layer-by-layer films on solid surfaces by electrostatic interaction between them. The direct electrochemistry of Mb was realized in {Au/Mb}n films at pyrolytic graphite (PG) electrodes, showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the Mb heme FeIII/FeII redox couple. Quartz crystal microbalance (QCM), electrochemical impedance spectroscopy (EIS), and CV were used to monitor or confirm the growth of the films. Compared with other Mb layer-by-layer films with nonconductive nanoparticles or polyions, {Au/Mb}n films showed much improved properties, such as smaller electron-transfer resistance (Rct) measured by EIS with Fe(CN)3-/4- redox probe, higher maximum surface concentration of electroactive Mb (Gamma*max), and better electrocatalytic activity toward reduction of O2 and H2O2, mainly because of the good conductivity of Au nanoparticles. Because of the high biocompatibility of Au nanoparticles, adsorbed Mb in the films retained its near native structure and biocatalytic activity. The size effect of Au nanoparticles on the electrochemical and electrocatalytic activity of Mb in {Au/Mb}n films was investigated, demonstrating that the {Au/Mb}n films assembled with smaller-sized Au nanoparticles have smaller Rct, higher Gamma*max, and better biocatalytic reactivity than those with larger size.     

Assembly of electroactive layer-by-layer films of myoglobin and ionomer poly(ester sulfonic acid)

Layer-by-layer films were assembled on solid substrates by alternate adsorption of negatively charged ionomer poly(ester sulfonic acid) or Eastman AQ55 from its aqueous dispersion and positively charged myoglobin (Mb) from its solution at pH 4.5. The film assembly process was monitored by cyclic voltammetry (CV), UV-vis spectroscopy, and quartz crystal microbalance (QCM). [AQ/Mb](n) films grown on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible CV peaks at about -0.20 V vs Ag/AgCl in pH 5.5 buffers, characteristic of the Mb heme Fe(III)/Fe(II) redox couple. Although the amount of Mb adsorbed in each bilayer was essentially the same, the fraction of electroactive Mb decreased dramatically with an increase of bilayer number (n). Soret absorption bands of [AQ/Mb](n) films on glass slides suggest that Mb in the films retains its native state in the medium pH range. Trichloroacetic acid, oxygen, and hydrogen peroxide were electrochemically catalyzed by [AQ/Mb](6) films with significant lowering of reduction overpotential.     

Facile cation electro-insertion into layer-by-layer assembled iron phytate films

Molecular layer-by-layer assembly from pre-saturated aqueous solutions of Fe³⁺ and phytate is employed to build up iron phytate deposits on tin-doped indium oxide (ITO) electrodes. Globular films with approximately 1 nm growth per layer are observed by AFM imaging and sectioning. In electrochemical experiments the iron phytate films show well-defined voltammetric responses consistent with an immobilised Fe(III/II) redox system in aqueous (LiClO₄, NaClO₄, KClO₄, phosphate buffer) and in ethanolic (LiClO₄, NaClO₄, NBu₄ClO₄) electrolyte solutions. The Fe(III/II) redox system is reversible and cation insertion/expulsion occurs fast on the timescale of voltammetric experiments even for more bulky NBu₄⁺ cations and in ethanolic solution. Peak shape analysis and scan rate dependent midpoint potentials suggest structural changes accompanying the redox process and limiting propagation. Iron phytate is proposed as a versatile and essentially colourless cation electro-insertion material and as a potential energy storage material.     

Preparation and characterization of hybrid cationic hydroxyethyl cellulose/sodium alginate polyelectrolyte antimicrobial films

This study aimed to develop polyelectrolyte‐structured antimicrobial food packaging materials that do not contain any antimicrobial agents. Cationic hydroxyethyl cellulose was synthesized and characterized by Fourier‐transform infrared, ¹H NMR, and ¹³C NMR spectroscopy. Its nitrogen content was determined by Kjeldahl method. Polyelectrolyte‐structured antimicrobial food packaging materials were prepared using hydroxyethyl cellulose, cationic hydroxyethyl cellulose, and sodium alginate. Antimicrobial activity of materials was defined by inhibition zone method (disc diffusion method). Thermal stability of samples was evaluated by thermal gravimetric analysis and differential scanning calorimetry. Surface morphology of samples was investigated by SEM. The obtained results prove that produced food packaging materials have good thermal and antimicrobial properties, and they can be used as food packaging material in many industries.     

Thermal modification of layer-by-layer assembled gold nanoparticle films

Gold nanoparticle films are assembled on glass and quartz substrates by a simple and highly efficient layer-by-layer deposition procedure that uses only commercially available cationic polymers. The film samples are then modified by heat curing in the temperature range of 25–1100 °C. The changes in the film conductance and colour with the curing temperature are related to the respective changes in micro-morphology of films on quartz as observed by scanning electron microscopy. In addition, we have demonstrated that the heat curing can embed the gold nanoparticle layer in the glass substrates. Because of the preparation simplicity and peculiar properties of these films, they could be used in various practical applications.     

Assembly of layer-by-layer films of electroactive hemoglobin and surfactant didodecyldimethylammonium bromide

When a solid substrate with negative surface charges was placed in an aqueous didodecyldimethylammonium bromide (DDAB) vesicle dispersion, the cationic surfactant DDAB with two hydrocarbon chains could be assembled into the biomembrane-like tail-to-tail double-layer structure on the solid surface with the positively charged head groups toward outside, making the surface charge reverse from negative to positive. After the solid substrate with DDAB was immersed in a hemoglobin (Hb) solution at pH 9.0, the negatively charged Hb was adsorbed on the surface of DDAB layer by electrostatic attraction, forming a DDAB/Hb film. By repeating this adsorption cycle, the {DDAB/Hb}(n) layer-by-layer films were assembled on solid surfaces, which was confirmed by UV-vis spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV). The stable {DDAB/Hb}(n) films assembled on pyrolytic graphite (PG) electrodes showed two pairs of nearly reversible redox peaks at about -0.22 and -1.14 V vs SCE in pH 7.0 buffers, characteristic of the Hb heme Fe(III)/Fe(II) and Fe(II)/Fe(I) redox couples, respectively. The direct electrochemistry of Hb in the films could be used to electrocatalyze reduction of various substrates. UV-vis and IR spectroscopic results and comparison experiments with {DDAB/hemin}(n) films indicate that Hb in the {DDAB/Hb}(n) films essentially retains its native structure. Atomic force microscopy (AFM) was used to characterize the morphology of the films with different outermost layers.     

Layer-by-layer assembled films of cellulose nanowires with antireflective properties

Natural nanowires (NWs) of cellulose obtained from a marine animal tunicate display surprisingly high uniformity and aspect ratio comparable with synthetic NWs. Their layer-by-layer assembled (LBL) films show strong antireflection (AR) properties having an origin in a novel highly porous architecture reminiscent of a "flattened matchsticks pile", with film-thickness-dependent porosity and optical properties created by randomly oriented and overlapping NWs. At an optimum number of LBL deposition cycles, light transmittance reaches nearly 100% (lambda approximately 400 nm) when deposited on a microscope glass slide and the refractive index is approximately 1.28 at lambda = 532 nm. In accordance with AR theory, the transmittance maximum red-shifts and begins to decrease after reaching the maximum with increasing film thickness as a result of increased light scattering. This first example of LBL layers of cellulose NWs can be seen as an exemplary structure for any rigid axial nanocolloids, for which, given the refractive index match, AR properties are expected to be a common property. Unique mechanical properties of the tunicate NWs are also a great asset for optical coatings.     

Electroactive porous films of myoglobin within calcium alginate

In this work, a novel two-step construction strategy for protein assembly films was proposed. The first step was the preparation of porous calcium alginate (CA) films by spraying calcium chloride (CaCl₂) solution over the mixture surface of sodium alginate and polyethylene glycol on various solid substrates. The second step involved the cast of myoglobin (Mb) onto the porous CA films and then formed the electroactive porous Mb-CA films. The nitrogen adsorption desorption isotherm, scanning electron microscope, alternating current impendence and cyclic voltammetry were used to characterize the porous films. Fully hydrated porous CA films had nearly 90 wt% water contents and UV–vis showed that Mb in the porous films retained its near native conformation at medium pH. The stable films modified on glassy carbon electrode demonstrated good electroactivity in protein-free buffer, which was originated from protein heme Fe(III)/Fe(II) redox couples. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (k _s) and formal potential (E ^o′) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. It was observed that the formal potential of the Mb Fe(III)/Fe(II) couple in porous CA films shifted linearly between pH 4.0 and 11.0 with a slope of −52.7 mV/pH, suggesting that one proton transfer was coupled to each electron transfer in the electrochemical reaction. The porous Mb-CA films showed the electrocatalytic activity toward dioxygen, hydrogen peroxide, and nitrite with significant decreases in the electrode potential required, and exhibited good operational and storage stability, reproducibility and fast response time for H₂O₂ detection. It is showing the possible future application of the films for biosensors and biocatalysis.     

Spontaneous wrinkling of layer-by-layer assembled polyelectrolyte films for humidity-responsive superhydrophobicity

The fabrication of smart films with reversible wettability enabled by the stimulus-induced morphology changes has attracted growing interest but remains a challenge. Here we report a smart film that can reversibly changes its wettability between transparent hydrophobicity to translucent superhydrophobicity through the humidity-induced wrinkling/de-wrinkling process. The film was fabricated by depositing hydrophobic SiO₂ nanoparticles (NPs) on poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) films, followed by partially exfoliating the films from the underlying substrates. The partially exfoliated PAA/PAH film can reversibly wrinkle and de-wrinkle when being alternately subjected to humid and dry environments. The deposition of hydrophobic SiO₂ NPs on the wrinkling PAA/PAH film does not hinder the humidity-enabled wrin-kling/de-wrinkling ability of the composite film. The hydrophobic SiO₂ NPs and the underlying humidity-wrinkling PAA/PAH film enable the composite film to spontaneously change from hydrophobic and transparent to superhydrophobic and translucent with the rise of environmental humidity.     

X-ray nanoscale profiling of layer-by-layer assembled metal/organophosphonate films

The nanoscale structure of multilayer metal/phosphonate thin films prepared via a layer-by-layer assembly process was studied using specular X-ray reflectivity (XRR), X-ray fluorescence (XRF), and long-period X-ray standing wave (XSW) analysis. After the SiO(2) X-ray mirror surfaces were functionalized with a monolayer film terminated with phosphonate groups, the organic multilayer films were assembled by alternating immersions in (a) aqueous solutions containing Zr(4+), Hf(4+), or Y(3+) cations and then (b) organic solvent solutions of PO(3)-R-PO(3), where R was a porphyrin or porphyrin-square spacer molecule. The different heavy metal cations provided X-ray fluorescence marker layers at different heights within the different multilayer assemblies. The XSW measurements used a 22 nm period Si/Mo multilayer mirror. The long-period XSW generated by the zeroth-order (total external reflection) through fourth-order Bragg diffraction conditions made it possible to examine the Fourier transforms of the fluorescent atom distributions over a much larger q(z)() range in reciprocal space than previously achieved.     

Direct electron transfer and electrocatalysis of hemoglobin in layer-by-layer films assembled with Al-MSU-S particles

In this paper, layer-by-layer (LBL) {MSU/Hb}(n)/PDDA films assembled by alternate adsorption of positively charged hemoglobin (Hb) and negatively charged mesoporous molecular sieves of Al-MSU-S onto a glassy carbon electrode (GCE) were reported. Al-MSU-S was synthesized by the precursor of zeolite Y and ionic liquids 1-hexadecane-3-methylimidazolium bromide (CMIMB) as a template in basic medium. It exhibited larger pore diameter, pore volume and surface area. Direct electrochemical and electrocatalytic properties of Hb in these layer-by-layer films were investigated. A pair of well-defined nearly reversible cyclic voltammetric peaks was observed and the formal potential of the heme Fe(III)/Fe(II) redox couple was found to be -0.295V (vs. SCE). The influences of layer's number and the pH of the external solution to the electron transfer behavior of Hb in {MSU/Hb}(n)/PDDA films were also estimated by cyclic voltammetry and a set of optimized conditions for film fabrication was inferred. The hemoglobin in{MSU/Hb}(n)/PDDA films displayed a good electrocatalytic activity to the reduction of hydrogen peroxide, which had linear current responses from 1.0 x 10(-6) to 1.86 x 10(-4)mol/L with the detection limit of 5.0 x 10(-7)mol/L (S/N=3). The apparent Michaeli-Menten constant (K(m)(app)) was 0.368 mmol/L. Thus, this methodology shows potential application of the preparation of third-generation biosensors.     

Layer-by-layer films of hemoglobin or myoglobin assembled with zeolite particles: electrochemistry and electrocatalysis

Positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 in solutions and negatively charged zeolite particles in dispersions were alternately adsorbed onto solid surfaces forming [zeolite/protein](n) layer-by-layer films, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The protein films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV peaks at about -0.35 V vs. SCE at pH 7.0, characteristic of the heme Fe(III)/Fe(II) redox couples. Hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)) in solution were catalytically reduced at [zeolite/protein](7) film modified electrodes, and could be quantitatively determined by CV and amperometry. The shape and position of infrared amide I and II bands of Hb or Mb in [zeolite/protein](7) films suggest that the proteins retain their near-native structure in the films. The penetration experiments of Fe(CN)(6)(3-) as the electroactive probe into these films and scanning electron microscopy (SEM) results indicate that the films possess a great amount of pores or channels. The porous structure of ]zeolite/protein](n) films is beneficial to counterion transport, which is crucial for protein electrochemistry in films controlled by the charge-hopping mechanism, and is also helpful for the diffusion of catalysis substrates into the films. The proteins with negatively charged net surface charges at pH 9.0 were also successfully assembled with like-charged zeolite particles into layer-by-layer films, although the adsorption amount was less than that assembled at pH 5.0. The possible reasons for this were discussed, and the driving forces were explored.     

肌红蛋白在海藻酸钠水凝胶中的电化学和电催化特性

海藻酸钠(Sodium Alginate,SA)是由L-葡萄糖醛酸与D-甘露糖醛酸组成的高分子线性糖醛酸,常作为固定化酶包埋材料。本文研究了海藻酸钠水凝胶膜中的肌红蛋白在磷酸盐缓冲溶液中的直接电化学和酶催化性质,探讨了测定H2O2和NO2^-的可能性。     

(−)-Epigallocatechin gallate/gelatin layer-by-layer assembled films and microcapsules

A new type of protein/polyphenol microcapsules on the basis of naturally occurring polyphenol (−)-epigallocatechin gallate (EGCG) and gelatin, type A, was obtained using the layer-by-layer (LbL) assembly method. The microcapsules show a more pronounced dependence of permeability on molecular weight of permeating substances than commonly used polyallylamine/polystyrene sulfonate capsules. The regularities of EGCG adsorption in alternation with type A and B gelatins have been investigated using quartz crystal microbalance and electrophoretic mobility measurements on microparticles and found to be dependent on gelatin properties. EGCG in the LbL assemblies retains its antioxidant activity. The kinetics of the reaction of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) cation-radicals with films consisting of 1–10 gelatin/EGCG bilayers is affected by film structure. The EGCG content in the protein/polyphenol film material is as high as 30% w/w. Encapsulation of EGCG via its alternated adsorption with gelatins can be a perspective way to new formulations containing the polyphenol for drug delivery applications.     

Electrochemical and electrocatalytic properties of myoglobin and hemoglobin incorporated in carboxymethyl cellulose films

Protein-CMC films were made by casting a solution of myoglobin (Mb) or hemoglobin (Hb) and carboxymethyl cellulose (CMC) on pyrolytic graphite electrodes. In pH 7.0 buffers, Mb and Hb incorporated in CMC films gave a pair of well-defined and quasi-reversible cyclic voltammetric peaks at about -0.34 V vs. SCE, respectively, characteristic of heme Fe(III)/Fe(II) redox couples of the proteins. The electrochemical parameters such as apparent standard heterogeneous electron transfer rate constants (k(s)) and formal potentials (E degrees ') were estimated by square wave voltammetry with nonlinear regression analysis. In aqueous solution, stable CMC films absorbed large amounts of water and formed hydrogel. Scanning electron microscopy of the films showed that interaction between Mb or Hb and CMC would make the morphology of dry protein-CMC films different from the CMC films alone. Positions of Soret absorbance band suggest that Mb and Hb in CMC films retain their secondary structure similar to the native states in the medium pH range. Trichloroacetic acid, nitrite, oxygen, and hydrogen peroxide were catalytically reduced at protein-CMC film electrodes.     

Preparation and properties of epichlorohydrin-cross-linked chitosan/hydroxyethyl cellulose based CuO nanocomposite films

This study introduces an effective route to fabricate chitosan (CS)-based film. The films were prepared through cross-linking reaction between CS and hydroxyethyl cellulose (HEC) using epichlorohydrin (ECH) as the cross-linker and simultaneously in-situ loading with CuO nanoparticles. FT-IR and loading efficiency results indicated the occurrence of inter- and intra-molecular cross-linking reaction between CS and HEC. XRD and EDS analyses showed that the CuO nanoparticles were evenly deposited onto CS film matrixes. SEM characterization showed that the films were of compact, dense and uniform cross morphologies, as well as obvious voids. The films also exhibited desired swelling ratio and water vapor permeability. The enhanced tensile strength was obtained with a maximum value of 77.02?±?3.26 MPa, while the stretch-ability slightly decreased. The thermal stability of the films decreased after cross-linking with HEC. The antibacterial ability of the films was generally improved with the increase of HEC and ECH contents.

Graphical abstract

Preparation and properties of epichlorohydrin-cross-linked chitosan/hydroxyethyl cellulose based CuO nanocomposite films

     

The selective and enhanced adsorptive behaviors of supramolecular recrystallized 1,3,5-benzenetricarboxylic acid assembled nano-bacterial cellulose

The effluent discharge produced in the textile printing and dyeing, leather and other fields, will cause the irreversible environmental pollution and extremely threatening safety of living organisms. The appropriate and efficient disposal method of dyestuff originated wastewater has been widely concerned in the past decades. In this study, the recrystallization of 1,3,5-benzene tricarboxylic acid (RCTMA) was put forward via a hydrothermal method to form the supramolecular RCTMA-based hexamer and thereafter assembled into the porous nano-bacterial cellulose (NBC) to construct the RCTMA@NBC composite. The morphology and surface properties of RCTMA@NBC were examined by scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy. This RCTMA@NBC was employed to adsorb methylene blue (MB) adjusting the pH, temperature, and dosage of adsorbent. The result showed the maximal absorption capacity of RCTMA@NBC appeared under pH = 7.1 and higher temperature will hinder the adsorption of dyes. Moreover, the adsorption isotherms and kinetics were evaluated which was more confirmed to Langmuir model and quasi-second-order kinetic equation, and the simulated maximum adsorption capacities of MB was 1162.12 mg/g. Moreover, cationic golden XGL and anionic brilliant crocein were selected to further verify the distinct adsorptive behavior. The excellent affinity towards cationic dyes proved the easy combination was based on the chemical force originated from mutual attraction between opposite charges, π–π interactions, and H-bonding, whereas the poor attraction for brilliant crocein was due to the electrostatic repulsion between sulfonic and carboxyl groups. The synthesized RCTMA@NBC possesses higher efficiency and selective adsorption, which exhibits the promising potential in the field of precise treatment of organic dye wastewater.     

Characterization of gamma irradiated carboxymethyl cellulose (CMC) films loaded with metal salts and fertilizers

Carboxymethyl cellulose (CMC) films loaded with different metal ions and fertilizers have been successfully prepared by the solution casting technique. The prepared films were subjected to different doses of gamma radiation at room temperature. The preparation conditions such as effect of type of metals, fertilizers and radiation dose on gel fraction (%) and swelling (%) were investigated. The maximum value of gel fraction was obtained at 10 kGy radiation dose. The formation of CMC/metal complexes was confirmed by X-ray diffraction (XRD), infrared spectroscopy and scanning electron microscope (SEM) which confirm the existence of possible interaction between CMC and metal ions. The loading of various metal ions to CMC films were found to enhance the mechanical properties of the prepared films. The results provided confirmation that metal coordination between the metal cation and the carboxylate group of CMC occurred.