Electroactive core-shell nanocluster films of heme proteins, polyelectrolytes, and silica nanoparticles

Novel protein core-shell nanocluster films were assembled layer by layer on solid surfaces. In the first step, positively charged heme protein hemoglobin (Hb) or myoglobin (Mb) and negatively charged poly(styrenesulfonate) (PSS) were alternately adsorbed on the surface of SiO2 nanoparticles, forming core-shell SiO2-(protein/PSS)m nanoclusters. In the second step, the SiO2-(protein/PSS)m nanoclusters and polycationic poly(ethylenimine) (PEI) were assembled layer by layer on various solid substrates, forming [[SiO2-(protein/PSS)m]/PEI]n films. Various techniques were used to characterize the nanoclusters and monitor the film growth. [[SiO2-(protein/PSS)m]/PEI]n films at pyrolytic graphite (PG) electrodes exhibited well-defined, chemically reversible cyclic voltammetric reduction-oxidation peaks characteristic of the heme Fe(III)/Fe(II) redox couples. The proteins in the films retained near native conformations in the medium pH range, and the films catalyzed electrochemical reduction of oxygen and hydrogen peroxide. Advantages of the nanocluster films over the simple [SiO2/protein]n layer-by-layer films include a larger fraction of electroactive protein and higher specific biocatalytic activity. Using this approach, biocatalytic activity can be tailored and controlled by varying the number of bilayers deposited on the nanoparticle cores and the number of nanocluster layers on electrodes.     

Comparative bioelectrochemical study of core-shell nanocluster films with ordinary layer-by-layer films containing heme proteins and CaCO3 nanoparticles

Negatively charged heme protein hemoglobin (Hb) or myoglobin (Mb) at pH 9.0 and positively charged poly(diallyldimethylammonium) (PDDA) were alternately adsorbed on the surface of CaCO(3) nanoparticles, forming core-shell CaCO(3)-[PDDA/(protein/PDDA)(m)] ([protein-m]) nanoclusters. Oppositely charged [protein-m] and poly(styrenesulfonate) (PSS) were then assembled layer by layer on various solid substrates, forming {[protein-m]/PSS}(n) films. In the meantime, ordinary layer-by-layer films of heme proteins with CaCO(3) nanoparticles ({protein/CaCO(3)}(n)) were also grown on solid surfaces. Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV) were used to characterize the nanoclusters and monitor the growth of the two types of films. Both kinds of protein films assembled on pyrolytic graphite (PG) electrodes exhibited well-defined, nearly reversible CV reduction-oxidation peaks, characteristic of heme Fe(III)/Fe(II) redox couples, and were used to catalyze the electrochemical reduction of hydrogen peroxide. The {[protein-m]/PSS}(n) films demonstrate distinct advantages over the {protein/CaCO(3)}(n) films due to their larger fraction of electroactive proteins, higher catalytic efficiency, and better thermostability. The penetration experiments of the electroactive probe into these films indicate that the {[protein-m]/PSS}(n) nanocluster films possess more pores or channels than the simple {protein/CaCO(3)}(n) films, which may be beneficial to counterion transport in the charge-hopping mechanism and helpful for the diffusion of catalysis substrates into the films. In addition, the electrochemical and biocatalytic activity of protein nanocluster films can be tailored by controlling the number of bilayers assembled on the nanoparticle cores (m) as well as the film thickness or the number of nanocluster layers on the electrodes (n).     

Electroactive layer-by-layer films of heme protein-coated polystyrene latex beads with poly(styrene sulfonate)

In this work, a novel two-step construction strategy for protein layer-by-layer assembly films was proposed. In the first step, positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 was adsorbed on the negatively charged surface of 500 nm diameter-sized polystyrene (PS) latex beads, forming core-shell structured PS-protein particles. In the next step, the PS-protein particles were further assembled layer by layer with oppositely charged poly(styrene sulfonate)(PSS) on various solid surfaces under suitable conditions. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), and UV-vis spectroscopy were used to monitor the growth of {(PS-protein)/PSS}(n) films. The stable {(PS-protein)/PSS}(n) films modified on pyrolytic graphite (PG) electrodes demonstrated good electroactivity in protein-free buffer, which was originated from protein heme Fe(III)/Fe(II) redox couples, and the electroactivity extended to six (PS-protein)/PSS bilayers. UV-vis spectroscopy showed that Hb and Mb in the films retained their near-native structure in the medium pH range. {(PS-protein)/PSS}(n) films catalyzed electrochemical reduction of oxygen, hydrogen peroxide, trichloroacetic acid (TCA) and nitrite with a significant lowering of overpotential, and displayed better catalytic activity than corresponding cast PS-protein films.     

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.     

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.     

Multilayers of oppositely charged SiO2 nanoparticles: effect of surface charge on multilayer assembly

The growth behavior of all-silica nanoparticle multilayer thin films assembled via layer-by-layer deposition of oppositely charged SiO2 nanoparticles was studied as a function of assembly conditions. Amine-functionalized SiO2 nanoparticles were assembled into multilayers through the use of three different sizes of negatively charged SiO2 nanoparticles. The assembly pH of the nanoparticle suspensions needed to achieve maximum growth for each system was found to be different. However, the surface charge /z/ of the negatively charged silica nanoparticles at the optimal assembly pH was approximately the same, indicating the importance of this parameter in determining the growth behavior of all-nanoparticle multilayers. When /z/ of the negatively charged nanoparticles lies between 0.6z(0) and 1.2z(0) (where z(0) is the pH-independent value of the zeta-potential of the positively charged nanoparticles used in this study), the multilayers show maximum growth for each system. The effect of particle size on the film structure was also investigated. Although nanoparticle size significantly influenced the average bilayer thickness of the multilayers, the porosity and refractive index of multilayers made from nanoparticles of different sizes varied by a small amount. For example, the porosity of the different multilayer systems ranged from 42 to 49%. This study further demonstrates that one-component all-nanoparticle multilayers can be assembled successfully by depositing nanoparticles of the same material but with opposite surface charge.     

Conductive effect of gold nanoparticles encapsulated inside polyamidoamine (PAMAM) dendrimers on electrochemistry of myoglobin (Mb) in {PAMAM-Au/Mb}(n) layer-by-layer films

PAMAM-Au nanocomposites prepared by reduction of HAuCl4 with NaBH4 in the presence of the sixth-generation polyamidoamine (PAMAM) took a unique structure, in which the 2 nm-sized Au nanoparticles were encapsulated in the interior cavities of the PAMAM molecules. The PAMAM-Au nanocomposites as a new type of nanomaterial were assembled layer-by-layer with myoglobin (Mb) into {PAMAM-Au/Mb}n films on solid surfaces, which was confirmed by quartz crystal microbalance (QCM), UV-vis spectroscopy, and cyclic voltammetry (CV). The direct electrochemistry of Mb in the films assembled on pyrolytic graphite (PG) electrodes was realized and used to catalyze the reduction of hydrogen peroxide. As compared to {PAMAM/Mb}n films containing no Au nanoparticles, the {PAMAM-Au/Mb}n films showed much better electrochemical and electrocatalytic properties, indicating the conductive effect of Au nanoparticles inside PAMAM on bridging electron transfer between Mb and PG electrodes.     

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.     

Direct electrochemistry of hemoglobin in layer-by-layer films with poly(vinyl sulfonate) grown on pyrolytic graphite electrodes

Stable layer-by-layer electroactive films were grown on pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanionic poly(vinyl sulfonate) (PVS) and positively charged hemoglobin (Hb) from their aqueous solutions. Cyclic voltammetry (CV) of [PVS/Hb]n films showed a pair of well-defined and nearly reversible peaks at about - 0.28 V vs. SCE at pH 5.5, characteristic of Hb heme Fe(III)/Fe(II) redox couple. The process of (PVS/Hb) bilayer growth was monitored and confirmed by CV, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. While the amount of Hb adsorbed in each bilayer was the same, the amount of electroactive Hb in each bilayer decreased dramatically with increase of the number of bilayer, and electroactivity was just extended to 8 [PVS/Hb] bilayers. CVs of [PVS/Hb]8 films maintained stable in buffers containing no Hb. Positions of Soret band of Hb in [PVS/Hb]n films grown on transparent glass slides suggest that Hb in the films keeps its secondary structure similar to its native state in a wide pH range. Trichloroacetic acid and nitrite were catalytically reduced by [PVS/Hb]8 films with significant lowering of the electrode potential required.     

血红蛋白和SiO2凝胶层层组装膜在碳纳米管/金纳米粒子修饰电极界面上的直接电化学及电催化研究

以SiO2凝胶膜和蛋白质交互组装法固定血红蛋白(Hb), 对其进行了电化学和电催化研究. 首先制备碳纳米管/金纳米粒子复合材料修饰的MWNTs-Au/GC电极, 为防止蛋白质在电极表面流失, 将Hb和自制的SiO2凝胶膜交替滴涂到电极表面, 得到SiO2/Hb层层组装膜修饰电极, 即{SiO2/Hb}n/MWNTs-Au/GC电极, n=2为优化层数. Hb在{SiO2/Hb}2/MWNTs-Au/GC电极上仍能保持其特有的生物活性, 并能与电极进行稳定快速的电子直接转移, 同时表现出过氧化物酶特性, 对H2O2具有良好的生物电催化还原能力.     

Interaction between myoglobin and hyaluronic acid in their layer-by-layer assembly: quartz crystal microbalance and cyclic voltammetry studies

Myoglobin (Mb), with different net surface charges at different pH in buffers and negatively charged hyaluronic acid (HA) at pH 5.0 in solutions were alternately adsorbed onto various solid surfaces and successfully assembled into {Mb/HA}(n) layer-by-layer films. The Mb in {Mb/HA}(n) films showed a quasi-reversible cyclic voltammetry (CV) response for its heme Fe(III)/Fe(II) redox couple. Quartz crystal microbalance (QCM) and CV were used to confirm the film growth and characterize the films. The interaction between Mb and HA and the influencing factors for Mb adsorption on HA surface, such as pH, Mb concentration, and ionic strength, were investigated in detail. The assembly driving force for {Mb/HA}(n) films, especially for the films assembled with like-charged Mb and HA, was found to be of electrostatic origin, while the secondary interaction such as hydrophobic interaction also plays an important role in some circumstances. Although the growth of {Mb(pH 7.0)/HA}(n) and {Mb(pH 9.0)/HA}(n) films was linear with the adsorption step, the exponential growth of {Mb(pH 5.0)/HA}(n) films was observed, especially when the films became thick. This exponential increase of mass and thickness with deposition step for {Mb(pH 5.0)/HA}(n) films was most probably attributed to the diffusion mechanism in which some HA molecules could diffuse in to and out of the whole films during the film assembly. Atomic force microscopy (AFM) results supported this speculation. UV-vis and IR spectroscopies of {Mb/HA}(n) films, combined with the comparative CV experiments of {Mb/HA}(n) and {catalase/HA}(n) films, suggest that Mb in the {Mb/HA}(n) multilayer films retains its near-native structure.     

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.     

Alternate assemblies of platinum nanoparticles and metalloporphyrins as tunable electrocatalysts for dioxygen reduction

Through electrostatic layer-by-layer (LBL) assembly, negatively charged citrate-stabilized platinum nanoparticles (PtNPs) and positively charged [tetrakis(N-methylpyridyl)porphyrinato] cobalt were alternately deposited on a 4-aminobenzoic acid-modified glassy carbon electrode and also on indium tin oxide substrates, directly forming the three-dimensional nanostructured materials. Thus-prepared multilayer films were characterized by UV--visible spectroscopy, surface plasmon resonance (SPR) spectroscopy, atomic force microscopy (AFM), and cyclic voltammetry. Regular growth of the multilayer films is monitored by UV--visible spectroscopy and SPR spectroscopy. AFM provides the morphology of the multilayer films. The PtNPs containing multilayer films exhibit high electrocatalytic activity for the reduction of dioxygen with high stability. Rotating disk electrode voltammetry and rotating ring-disk electrode voltammetry demonstrate that the PtNP-containing multilayer films can catalyze an almost four-electron reduction of O(2) to H(2)O in an air-saturated 0.5 M H(2)SO(4) solution. Furthermore, the electrocatalytic activity of the films could be further tailored by simply choosing different cycles in the LBL process or more specifically the amount of the assembly components in the films. The high electrocatalytic activity and good stability for dioxygen reduction make the PtNP-containing multilayer films potential candidates for the efficient cathode material in fuel cells.     

Electrochemical and electrogenerated chemiluminescence of clay nanoparticles/Ru(bpy)(3)(2+) multilayer films on ITO electrodes

The electrochemical and electrogenerated chemiluminescence of Ru(bpy)(3)(2+) immobilized in [clay/Ru(bpy)(3)(2+)](n) multilayer films by layer-by-layer assembly were investigated. The stable multilayer films of clay and Ru(bpy)(3)(2+) were assembled by alternate adsorption of negatively charged clay platelets and positively charged Ru(bpy)(3)(2+) from their aqueous dispersions. UV-vis spectroscopy, quartz crystal microbalance (QCM), cyclic voltammetry, and electrogenerated chemiluminescence (ECL) were used to monitor the immobilization of Ru(bpy)(3)(2+) and the regular growth of the [clay/Ru(bpy)(3)(2+)](n) multilayer films. The multilayer films modified electrode was used for the ECL detection of tripropylamine (TPA) and oxalate. The proposed novel immobilized method exhibited good stability, reproducibility and high sensitivity for the determination of TPA and oxalate, which mainly resulted from the contributing of clay nanoparticles with appreciable surface area, special structural features and unusual intercalation properties. Detection limits were 20 and 100 nM for TPA and oxalate, respectively and the linear concentration range extended from 60 nM to 0.66 mM for TPA.     

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.     

Salt-induced swelling and electrochemical property change of hyaluronic acid/myoglobin multilayer films

The ionic strength in supporting electrolyte solution had a significant influence on the electrochemical and electrocatalytic behaviors of myoglobin (Mb) in {HA/Mb}n films, which were assembled layer-by-layer on pyrolytic graphite (PG) electrodes with oppositely charged hyaluronic acid (HA) and Mb. The results of cyclic voltammetry (CV), quartz crystal microbalance (QCM), scanning electron microscopy (SEM), rotating disk voltammetry (RDV), and electrochemical impedance spectroscopy (EIS) showed that after incubation with testing solution at high concentration of salt (CKCl), the {HA/Mb}n films swelled and the film permeability was enhanced, suggesting that the external salt ions and accompanied water molecules in the exposure solution are incorporated into the films. Systematic investigation of the type and size effect of counterions in supporting electrolyte solution on the electrochemical responses for the {HA/Mb}n films and the positive shift of the formal potential (E degrees ') with CKCl suggest that it is cationic rather than anionic counterions that control the electrode process of {HA/Mb}n films at PG electrodes with electron hopping mechanism. The salt-induced swelling of {HA/Mb}n films facilitated the transportation of counterions, and then accelerated the electron transfer of Mb in the films with the underlying electrodes, making the film electrodes show better CV responses. The comparative study showed that only Mb layer-by-layer films assembled with "soft" and flexible polyions could demonstrate the salt-induced effect and that the {HA/Mb}n films showed better swelling capability than {PSS/Mb}n films (PSS = poly(styrenesulfonate)) due to the unique character of HA.     

Construction of hyaluronan-silver nanoparticle–hemoglobin multilayer composite film and investigations on its electrocatalytic properties

In this work, hyaluronan-silver nanoparticles (HSNPs) were prepared by UV-initiated photoreduction, and protein hemoglobin (Hb) was then alternately assembled with the prepared negatively charged HSNPs into layer-by-layer (LBL) films on solid surface. The electrochemical behavior and electrocatalytic activities toward oxygen and hydrogen peroxide of the resulting films were studied. It was found that the HSNPs greatly enhanced the electron transfer reactivity of Hb as a bridge. The assembly films showed a pair of nearly reversible redox peaks with a formal potential of −0.32 V (vs. Ag/AgCl) for the heme Fe(III)/Fe(II) redox couple. The immobilized Hb in the films maintained its biological activity, showing a surface-controlled process with a heterogeneous electron transfer rate constant (k _s) of 1.0 s⁻¹ and displaying the same features of a peroxidase in the electrocatalytic reduction of oxygen and hydrogen peroxide. This work provides a novel model to fabricate LBL films with protein, polysaccharide and nanoparticles, which may establish a foundation for fabricating new type of biosensors based on the direct electron transfer of redox proteins immobilized in nanocomposite multilayer films with underlying electrodes.     

多金属氧酸盐K17[Ce(P2Mo17O61)2]多层膜修饰电极的组装及其电化学行为

利用层接层自组装法(LbL), 制备出有序且稳定的多金属氧酸盐K17[Ce(P2Mo17O61)2]多层膜. 应用电化学, 紫外光谱和X射线光电子能谱等方法研究该化合物的电化学性质及其膜修饰电极的电化学性质.     

Loading behavior of {chitosan/hyaluronic acid}n layer-by-layer assembly films toward myoglobin: an electrochemical study

When {CS/HA}n layer-by-layer films assembled by oppositely charged chitosan (CS) and hyaluronic acid (HA) were immersed in myoglobin (Mb) solution at pH 5.0, Mb was gradually loaded into the {CS/HA}n films, designated as {CS/HA}n-Mb. The cyclic voltammetric (CV) peak pair of Mb FeIII/FeII redox couple for {CS/HA}n-Mb films on pyrolytic graphite (PG) electrodes was used to investigate the loading behavior of {CS/HA}n films toward Mb. The various influencing factors, such as the number of bilayers (n), the pH of Mb loading solution, and the ionic strength of solution, were investigated by different electrochemical methods and other techniques. The results showed that the main driving force for the bulk loading of Mb was most probably the electrostatic interaction between oppositely charged Mb in solution and HA in the films, while other interactions such as hydrogen bonding and hydrophobic interaction may also play an important role. Other polyelectrolyte multilayer (PEM) films with different components were compared with {CS/HA}n films in permeability and Mb loading, and electroactive probes with different size and surface charge were compared in their incorporation into PEM films. The results suggest that due to the unique structure of CS and HA, {CS/HA}n films with relatively low charge density are packed more loosely and more easily swelled by water, and have better permeability, which may lead to the higher loading amount and shorter loading time for Mb. The protein-loaded PEM films provide a new route to immobilize redox proteins on electrodes and realize the direct electrochemistry of the proteins.     

Stable superhydrophobic organic-inorganic hybrid films by electrostatic self-assembly

Organic-inorganic hybrid films were prepared through layer-by-layer (LBL) deposition of poly(allylamine hydrochloride) (PAH) and ZrO(2) nanoparticles coated with poly(acrylic acid) (PAA), allowing facile control of surface roughness and hydrophobicity. Superhydrophobic behavior was observed after deposition of silica nanoparticles and a simple fluorination of the surface. The structure of films was controlled by the number of deposition cycles using PAA-coated 100 nm ZrO(2) nanoparticles, the particle size, and the prelayer with PAH and PAA. The change in the apparent water contact angle of (PAH/PAA-coated ZrO(2)n surfaces without fluorination of the surface agrees with Cassie and Baxter's model for nonwetted surfaces even though the outermost surface itself is hydrophilic. Superhydrophobic surfaces were then successfully developed by the deposition of hydrophilic silica nanoparticles on a 10 bilayer surface of PAH/PAA-coated ZrO(2), and a simple fluorination. Moreover, the chemical stability of the film was greatly increased by heat-induced cross-linking of the film. The incorporation of ZrO(2) nanoparticles in superhydrophobic films promises better mechanical properties than the organic film.