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.     

pH-dependent behaviors of electroactive myoglobin loaded into layer-by-layer films assembled with alginate and hydroxyethyl cellulose ethoxylate

In the present work, strong polybase quaternized hydroxyethyl cellulose ethoxylate (HECE) and weak polyacid alginate (AA) were assembled into {HECE/AA} n layer-by-layer (LBL) films on electrodes by electrostatic interaction between them, and the films were then immersed in myoglobin (Mb) solution to load Mb into the films, designated as {HECE/AA}n-Mb. The {HECE/AA}n-Mb films showed a nearly reversible cyclic voltammetric (CV) peak pair at about -0.34 V vs SCE in pH 7.0 buffers for Mb heme Fe(III)/Fe(II) redox couple, and the surface concentration of electroactive Mb in the films (Gamma*) was affected significantly by the pH of Mb loading solution and testing solution. The amount of Mb loaded from pH 5.0 solution was much larger than that from pH 9.0 solution, which is mainly attributed to the higher degree of swelling, porosity, and permeability of {HECE/AA}n films at pH 5.0 than at pH 9.0. In addition, the electrostatic interaction between Mb and the AA component in the films might also play an important role in Mb loading. The pH of the testing solution where {HECE/AA}n-Mb films were tested by CV also influenced the Gamma* value, showing that the fraction of electroactive Mb among the total Mb loaded into the films increased remarkably as the pH of the testing solution decreased. This result is rationalized in terms of the pH-dependent film permeability toward counterions and the electron-hopping mechanism in electron transfer of redox proteins in the film phase. This model system may provide a general and effective approach to control the electroactivity of immobilized redox proteins in the multilayer assembly containing weak polyions by adjusting pH and may guide us to develop the new kind of controllable electrochemical biosensors based on the direct electrochemistry of enzymes.     

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.     

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.     

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.     

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).     

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.     

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.     

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 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.     

Influence of Ionic Strength on Electrochemical Responses of Myoglobin Loaded in Polysaccharide Layer‐by‐Layer Assembly Films

Two polysaccharides hydroxyethyl cellulose ethoxylate (HECE) and hyaluronic acid (HA) were assembled into {HECE/HA}_n layer‐by‐layer films on electrodes. The films were then immersed in myoglobin (Mb) solutions to load Mb into the films. The Mb‐loaded films showed a nearly reversible cyclic voltammetric (CV) peak pair at ?0.34 V vs. SCE in pH 7.0 buffers. The effect of ionic strength in Mb loading solutions and CV testing solutions on the CV response of the films was investigated. The direct electrochemistry of Mb loaded in the films could also be used to electrocatalyze the reduction of oxygen and H₂O₂ in solution.     

Electrochemical Investigation of Myoglobin in Layer‐by‐Layer Films Assembled with Sulfonated‐β‐Cyclodextrin

In this work, myoglobin (Mb) and sulfonated‐β‐cyclodextrin (S‐CD) were assembled into {S‐CD/Mb}_n layer‐by‐layer films on solid substrates. In pH 7.0 buffers, the {S‐CD/Mb}_n films assembled on electrodes showed a pair of well‐defined and nearly reversible CV peaks at about ?0.35 V vs. SCE. The stable CV response of {S‐CD/Mb}_n films could be used to electrocatalyze reduction of oxygen and hydrogen peroxide in solution. For comparison, another modified β‐cyclodextrin, carboxyethyl‐β‐cyclodextrin (C‐CD), was also assembled with Mb into {C‐CD/Mb}_n multilayer films. The driving forces of the assembly were explored and discussed.     

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.     

In situ electro-deposition of Pt micro-nano clusters on the surface of {[PMo12O40]3-/PAMAM}n multilayer composite films and their electrocatalytic activities regarding methanol oxidation

The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films are prepared by LBL electrostatic assembly technique, and their uniform and homogeneous traits have been verified by cyclic voltammetry. The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films with PAMAM as the outmost layer, having an open structure and exhibiting good penetrability for the solvent molecules at low pH, are used as matrices for electro-deposition of Pt micro-nano clusters in situ. X-ray photoelectron spectroscopy (XPS) analysis and field emission scanning electron microscope (FE-SEM) characterization show that the unique Pt micro-nano clusters with flower-like structure have been immobilized on the surface of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. The morphologies of Pt micro-nano clusters are influenced by electro-deposition conditions such as deposition potential, deposition time, and the number of layers of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. Pt(-clusters)-{PMo(12)/PAMAM}(3) composite films demonstrate good electrocatalytic activities regarding methanol oxidation and improved tolerance of CO.     

Direct Electrochemistry and Electrocatalysis of Myoglobin with Ionic Liquid through Multilayers Film on Carbon Ionic Liquid Electrode

Multilayers of myoglobin (Mb) with ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM]BF₄) was assembled on carbon ionic liquid electrode (CILE) based on the electrostatic attraction between the negatively charged Mb and the positively charged imidazolium ion of IL. The CILE was fabricated with 1‐ethyl‐3‐methylimidazolium ethylsulfate ([EMIM]EtOSO₃) as the modifier, which exhibited imidazolium ion on the electrode surface. Then Mb molecules were assembled on the surface of CILE step‐by‐step to get a {IL/Mb}_n multilayer film modified electrode. UV‐Vis adsorption and FT‐IR spectra indicated that Mb remained its native structure in the IL matrix. In deaerated phosphate buffer solution (pH 7.0) a pair of well‐defined quasi‐reversible redox peaks appeared with the apparent formal potential (E^0′) as ‐0.212 V (vs. SCE), which was the characteristic of Mb heme Fe(III)/Fe(II) redox couples. The results indicated that the direct electron transfer of Mb was realized on the modified electrode. The {IL/Mb}_n/CILE displayed excellent electrocatalytic ability to the trichloroacetic acid reduction in the concentration range from 2.0 to 22.0 mmol/L with the detection limit of 0.6 mmol/L (3σ). The proposed method provides a new platform to fabricate the third generation biosensor based on the self‐assembly of redox protein with ILs.     

Direct Electrochemistry of Hemoglobin in Layer-by-layer {PDDA/Hb}_n Films Assembled on Pyrolytic Graphite Electrodes

The principle of alternate adsorption can be used to design and control specific molecular architectures1. Protein-polyion layer-by-layer assembly opens a possibility of organizing proteins with specific molecular architectural plan1 and studying redox proteins with electrochemical methods2. Recently, we reported electrochemistry of layer-by-layer {PSS/Mb}n films grown on PG electrodes1. In this work, layer-by-layer {PDDA/Hb}n films were fabricated on PG electrodes. Electrochemistry and …     

Driving forces for layer-by-layer self-assembly of films of SiO2 nanoparticles and heme proteins

Heme protein hemoglobin (Hb) or myoglobin (Mb) and silica nanoparticles in a variety of charge states were assembled layer-by-layer into films on solid surfaces to investigate the driving forces for film assembly. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and UV-vis and reflectance absorption infrared (RAIR) spectroscopy were used to characterize the different [SiO2/protein]n films. Even when the proteins and silica were both negatively charged, stable layer-by-layer [SiO2/protein]n films were successfully fabricated, although amounts of protein were smaller than when nanoparticles and proteins had opposite charges. Results suggest the importance of localized Coulombic attractions between the negative nanoparticle surface and positively charged amino acid residues on the Mb or Hb surfaces in the assembly and for the stability of [SiO2/protein]n films.     

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.     

Electrochemistry and Electrocatalysis of Myoglobin Loaded into Multilayer Films Assembled with Phytic Acid and Chitosan

Natural polymer polysaccharides chitosan (CS) was successfully assembled with phytic acid (PA) into {PA/CS}_n layer-by-layer films. Myoglobin (Mb) could be gradually “absorbed” or loaded into {PA/CS}_n films when the films were immersed into Mb solutions, forming {PA/CS}_n-Mb films. The {PA/CS}_n-Mb films demonstrated well-defined and quasi-reversible cyclic voltammetry (CV) responses for Mb Fe^III/Fe^II redox couple and were used to catalyze electrochemical reduction of oxygen and hydrogen peroxide. The interaction between Mb and {PA/CS}_n films was explored and discussed, which suggested that the electrostatic attraction might play a major role in loading Mb into the films. This new kind of film incorporated with redox proteins could be used to fabricate the new type of biosensors or bioreactors without using mediators.