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.     

Layer-by-layer electrostatic self-assembly of anionic and cationic carbon nanotubes

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

Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.     

Transparent and flexible glucose biosensor via layer-by-layer assembly of multi-wall carbon nanotubes and glucose oxidase

This paper reports a transparent and flexible glucose biosensor of which multi-wall carbon nanotubes (MWNTs) and glucose oxidase (GOx) is layer-by-layer (LBL) self-assembled on a polymer substrate. A thin Ti and Au layers is firstly deposited on the polymer substrate through plasma immersion ion implantation (PIII) and sputtering, respectively. An organic monolayer then forms on the gold surface using thiol chemistry. Subsequently, negatively charged MWNTs and GOx are stably LBL assembled on the modified Au surface, respectively, via alternative electrostatic interaction of the positively charged polyelectrolyte with the oppositely charged MWNTs and GOx. Electrochemical studies show that the multilayer membrane exhibits remarkable electrocatalytic activity to detect glucose molecule. The biosensor displays a linear response range of 0.02–2.2 mM (a correlation coefficient of 0.998) with a low detection limit of 10 μM. This remarkable performance, combined with the large area preparation process, demonstrates this CNT-based multilayer biosensor is well suited for commercial applications.     

毛细管电泳-修饰电极电化学检测法测定饮用水中溴酸盐

通过静电组装技术在碳圆盘电极（PGE）表面制备{聚二烯丙基二甲基氯化铵（PDDA）/多壁碳纳米管（MWCNT）}n/PDDA多膜,并采用循环伏安法在多膜表面电化学修饰一磷钼酸（PMo12）膜,构筑PGE/{PDDA/MWNTs}5/PDDA/PMo12复合膜修饰电极,研究该复合膜修饰电极电化学及其对溴酸盐（BrO3-）电催化还原性质.在此基础上建立毛细管电泳-PGE/{PDDA/MWNTs}5/PDDA/PMo12修饰电极电化学检法定饮用水中溴酸盐分析新方法.在优化实验条件下,电泳峰面积与溴酸根浓度在5.0×10-8～5.0×10-5mol/L范围内呈良好性关系（r=0.9954）,检出为2.0×10-8mol/L（S/N=3）.     

In situ fabrication of silver nanoarrays in hyaluronan/PDDA layer-by-layer assembled structure

We present a simple in situ method to fabricate silver (Ag) nanoparticle arrays in a layer-by-layer (LBL) assembled hyaluronan (HA)/poly(dimethyldiallylammonium chloride) (PDDA) multilayer structure, in which the LBL multilayered film is constructed by electrostatic attraction between positively charged PDDA and negatively charged HA, followed by in situ synthesis of embedded Ag nanoparticle arrays in the LBL "nanoreactors," where the abundant negatively charged carboxyl groups of HA bind and further reduce Ag(+) ions under UV-irradiating. The arrays morphology is highly dependent on the number of bilayers, and the surface density of nanoparticles in the arrays can be simply tailored by the number of irradiation/drying cycles during fabrication. The embedded Ag nanoparticle arrays possess good stability for localized surface plasmon resonance (SPR) absorption spectrum-based biosensors and superior antimicrobial capability. These render great potentials for the films in both biosensing and antimicrobial applications.     

Fabrication of multilayer-film-modified gold electrode composed of myoglobin,chitosan, and polyelectrolyte-wrapped multi-wall carbon nanotubes by layer-by-layer assembled technique and electrochemical catalysis for hydrogen peroxide and trichloroacetic acid

Electroactive multilayer film of myoglobin (Mb)-, chitosan (CS)-, and poly(dimethyldiallylammonium chloride) (PDDA)-wrapped multi-wall carbon nanotubes (MWNTs) is fabricated on a gold electrode via layer-by-layer (LBL) technique. The assembled multilayer films is characterized by scanning electron microscopy (SEM), UV-vis spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). UV-vis spectroscopy showed that Mb in the films retained its near-native structure. The stable multilayerfilm-modified gold electrodes showed good electroactivity in protein-free buffer solution, which is originated from protein heme Fe(III)/Fe(II) redox couple. The modified electrode exhibited good electrocatalytic property toward reduction of H₂O₂ and trichloroacetic acid, indicating the potential application as amperometric biosensor. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 11, pp. 1366–1376. The text was submitted by the authors in English.     

Nanostructured biosensors built by layer-by-layer electrostatic assembly of enzyme-coated single-walled carbon nanotubes and redox polymers

In this study, we describe the construction of glucose biosensors based on an electrostatic layer-by-layer (LBL) technique. Gold electrodes were initially functionalized with negatively charged 11-mercaptoundecanoic acid followed by alternate immersion in solutions of a positively charged redox polymer, poly[(vinylpyridine)Os(bipyridyl)2Cl(2+/3+)], and a negatively charged enzyme, glucose oxidase (GOX), or a GOX solution containing single-walled carbon nanotubes (SWNTs). The LBL assembly of the multilayer films were characterized by UV-vis spectroscopy, ellipsometry, and cyclic voltammetry, while characterization of the single-walled nanotubes was performed with transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. When the GOX solution contained single-walled carbon nanotubes (GOX-SWNTs), the oxidation peak currents during cyclic voltammetry increased 1.4-4.0 times, as compared to films without SWNTs. Similarly the glucose electro-oxidation current also increased (6-17 times) when SWNTs were present. By varying the number of multilayers, the sensitivity of the sensors could be controlled.     

碳纳米管/聚二烯丙基二甲基氯化铵/磷钼酸复合膜的组装及其在溴酸盐检测中的应用

通过静电层层组装技术在玻碳(GC)电极表面制备{多壁碳纳米管(MWCNT)/聚二烯丙基二甲基氯化铵(PDDA)}n多层膜,并采用循环伏安法在多层膜的表面电化学修饰一层磷钼酸(PMo12)膜,构筑GC/{MWCNT/PDDA}n-PMo12复合膜修饰电极.利用SEM对比观察{MWCNT/PDDA}n和{PDDA/MWCNT}n-PMo12的微观结构,并研究该复合膜修饰电极的电化学及其对溴酸盐(BrO3-)电催化还原性质.在此基础上研发一种基于GC/{MWCNT/PDDA}n-PMo12复合膜修饰电极的电流型BrO3-传感器,该传感器表现出明显增大的响应电流.在最优的实验条件下,采用电流时间曲线(i-t)法考察该复合膜修饰电极对BrO3-的安培响应.实验结果表明,该传感器在BrO3-浓度为50～400nmol/L的范围内具有良好的线性关系,相关系数R2为0.9950,响应时间为1.53s,检出限为20nmol/L,灵敏度为13.81mA(mmol/L)-1cm-2.     

Chemometrics to evaluate the quality of water sources for human consumption

Multilayer films of multiwalled carbon nanotubes (MWNTs) were homogeneously and stably assembled on a glassy carbon (GC) electrode using the layer-by-layer (LBL) method based on electrostatic interaction between MWNTs (negatively charged) and a biopolymer chitosan (CHIT) (positively charged). Scanning electron microscopy (SEM) image of the resulting {CHIT/MWNTs}₉ film indicated that the substrate was mostly covered with MWNTs in the form of small bundles or single nanotubes. The multilayer film was used to study the electrocatalytic oxidation of NADH. The assembled {CHIT/MWNTs}₉/GC electrode could decrease the oxidation overpotential of NADH by more than 350 mV. The {CHIT/MWNTs}₉/GC electrode exhibited a wide linear response range of 8 × 10⁻⁷ to 1.6 × 10⁻³ mol · L⁻¹ with a correlation coefficient of 0.997 for the detection of NADH. The response time and detection limit (S/N = 3) were determined to be 3 s and 0.3 × 10⁻⁶ mol · L⁻¹, respectively. Another attractive characteristic was that the method was simple and the assembled {CHIT/MWNTs}₉/GC electrode was highly stable.     

Silver nanocomposite layer-by-layer films based on assembled polyelectrolyte/dendrimer

Silver nanocomposite multilayer films were prepared through the in situ method. Multilayer thin films, prepared through the sequential electrostatic deposition of a positively charged third-generation poly(amidoamine) dendrimer (PAMAM) and negatively charged poly(styrenesulfonate) (PSS) and poly(acrylic acid) (PAA), were utilized as nanoreactors for the formation of silver nanoparticles. The silver ions were preorganized in layer-by-layer (LBL) films composed of PAMAM dendrimers and subsequently reduced with hydrogen to prepare the silver nanoparticles. The UV-vis spectrum and profilometer were used to characterize the regular growth of bilayers. UV-vis absorption from plasmon resonance at 435 nm and TEM images indicated the formation of the silver nanoparticles in the multilayer films. The silver nanocomposite LBL films were also constructed on the indium tin oxide-glass and investigated using cyclic voltammetry. The silver nanoparticles in the multilayer films have a stronger negative redox potential. The silver nanocomposite LBL films may have a potential application in the catalysis of reduction of 4-nitrophenol with sodium borohydride.     

Copper(II)-mediated layer-by-layer assembly of viologenthiol-functionalized carbon nanotube hybrid multilayers: preparation, characterization, morphology, and electrochemical properties

The metal-mediated self-assembly of coordination polymers, building blocks, and metal-organic frameworks has been widely used to construct multifunctional novel materials on the molecular level. Here, we developed this technique to build up multilayers of functionalized carbon nanotubes on the basis of both intermolecular electrostatic and coordinative interactions. Positively charged electroactive viologenthiol (VSH) was first immobilized on multiwalled carbon nanotubes (MWNTs) to form MWNT-VSH hybrids with a relative content of ～9% by weight. Field emission transmission electron microscopy images revealed that the VSH molecules randomly covered the surfaces of MWNTs with a thickness of 1 to 2 nm. Then, the MWNT-VSH hybrids were used as nanoscale multidentate "ligands" (linkers) to construct metal-mediated multilayers with the use of CuAc(2) as the connectors by the layer-by-layer (LBL) method. The assembly process was monitored by absorption and X-ray photoelectron spectroscopy as well as scanning electron and atomic force microscopy after each assembly of Cu(II) ions and MWNT-VSH hybrids. Finally, the electrochemical behaviors of the viologens in the MWNT-VS/Cu LBL multilayers were investigated.     

Fabrication of free-standing multilayer films by using pH-responsive microgels as sacrificial layers

A facile way to prepare free-standing polyelectrolyte multilayer films of poly(sodium 4-styrenesulfonate)(PSS)/poly(diallyldimethylammonium)(PDDA) was developed by applying a new pH-dependent sacrificial system based on cross-linked poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) microgels. The tertiary amine groups of PDMAEMA microgels can be protonated in acidic environment, and the protonated microgels were deposited by layer-by-layer (LbL) technique with PSS. PSS/PDDA multilayer films were constructed on the top of the PSS/microgels sacrificial layers. The LbL assembly process was investigated by UV–vis spectroscopy. Further study shows that the free-standing PSS/PDDA multilayer films can be obtained within 3 min by treating the as-prepared films in alkali aqueous solution with a pH of 12.0. The pH-triggered exfoliation of PSS/PDDA multilayer films provides a simple and facile way to prepare LbL assembled free-standing multilayer films.     

层层自组装技术制备PDDA-多壁碳纳米管-胆碱生物传感器

以PDDA分散多壁碳纳米管(MWCNTs),制得PDDA-MWCNTs悬浮液,采用层层自组装技术将PDDA-MWCNTs与胆碱氧化酶(ChOx)交替组装在铂(Pt)电极上,最后滴加Nafion制备抗干扰膜,构建了电流型胆碱生物传感器。实验结果表明,构建的复合酶膜(PDDA-MWCNTs/ChOx)n对底物胆碱的催化电流随着组装层数增多而明显增大,酶膜组装6层时最优。此传感器在5×10-6～2.5×10-4mol/L浓度范围内对胆碱有良好线性范围,响应时间为6.6s;灵敏度为21.97μA/mmol;检出限为2×10-6mol/L(S/N=3),RSD<5%,且传感器抗干扰能力强、稳定性好。     

Multilayer films of carbon nanotubes and redox polymer on screen-printed carbon electrodes for electrocatalysis of ascorbic acid

Multilayer films containing multiwall carbon nanotubes and redox polymer were successfully fabricated on a screen-printed carbon electrode using layer-by-layer (LBL) assembled method. UV-vis spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and electrochemical method were used to characterize the assembled multilayer films. The multilayer films modified electrodes exhibited good electrocatalytic activity towards the oxidation of ascorbic acid (AA). Compared with the bare electrode, the oxidation peak potential negatively shifted about 350 mV (versus Ag/AgCl). Furthermore, the modified screen-printed carbon electrodes (SPCEs) could be used for the determination of ascorbic acid in real samples.     

碳纳米管修饰电极同时测定邻苯二酚和对苯二酚

用十二烷基磺酸钠(SDS)分散碳纳米管(CNTs),通过层层组装(LBL)聚二甲基二烯丙基氯化铵(PDDA)和CNTs构筑PDDA/CNTs多层膜电极.利用紫外-可见光谱法对PDDA/CNTs多层膜的组装过程进行监测,用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了邻苯二酚和对苯二酚同时存在时PDDA/CNTs多层膜电极上的电化学行为.结果表明,碳纳米管修饰电极对邻苯二酚和对苯二酚有较好的电催化活性和电分离作用,邻苯二酚和对苯二酚无需经过分离即可同时被检出.在修饰电极上的线性范围如下:邻苯二酚为2.0×10-6~1.4×10-4mol/L,线性相关系数R=0.9991;对苯二酚为2.0×10-6~1.4×10-4mol/L,线性相关系数R=0.9987.     

Carbon Nanotubes‐Based Amperometric Cholesterol Biosensor Fabricated Through Layer‐by‐Layer Technique

A carbon nanotubes‐based amperometric cholesterol biosensor has been fabricated through layer‐by‐layer (LBL) deposition of a cationic polyelectrolyte (PDDA, poly(diallyldimethylammonium chloride)) and cholesterol oxidase (ChOx) on multi‐walled carbon nanotubes (MWNTs)‐modified gold electrode, followed by electrochemical generation of a nonconducting poly(o‐phenylenediamine) (PPD) film as the protective coating. Electrochemical impedance measurements have shown that PDDA/ChOx multilayer film could be formed uniformly on MWNTs‐modified gold electrode. Due to the strong electrocatalytic properties of MWNTs toward H₂O₂ and the low permeability of PPD film for electroacitve species, such as ascorbic acid, uric acid and acetaminophen, the biosensor has shown high sensitivity and good anti‐interferent ability in the detection of cholesterol. The effect of the pH value of the detection solution on the response of the biosensor was also investigated. A linear range up to 6.0 mM has been observed for the biosensor with a detection limit of 0.2 mM. The apparent Michaelis‐Menten constant and the maximum response current density were calculated to be 7.17 mM and 7.32 μA cm^?2, respectively.     

Double-layered TiO2-SiO2 nanostructured films with self-cleaning and antireflective properties

Dual function of self-cleaning and antireflection can be created in double-layered TiO2-SiO2 nanostructured films. The film were prepared by (1) layer-by-layer deposition of multilayered SiO2 nanoparticles with polydiallyldimethylammonium (PDDA) cations, (2) layer-by-layer deposition of multilayered titanate nanosheets with polications on PDDA/SiO2 multilayer films, and (3) burning out the polymer and converting titanate nanosheets into TiO2 by hearing at 500 degrees C. The as-prepared films, consisting of a porous SiO2 bottom layer and a dense TiO2 top layer, improved the transmittance of glass or quartz substrates, as demonstrated by transmission spectra collected at normal incidence. The photocatalytic properties of the films were studied by the change of the water contact angle together with the decay of the IR absorption of the hydrocarbon chain of octadecylphosphonic-acid-modified films under 2.6 mW cm-2 UV illumination. Both the antireflective and the photocatalytic properties of the films were dependent on the number of PDDA/nanosheet bilayers deposited. however, excellent surface wettability of the films for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the double-layered nanostructured film.     

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.     

Graphene as a spacer to layer-by-layer assemble electrochemically functionalized nanostructures for molecular bioelectronic devices

This study demonstrates the capability of graphene as a spacer to form electrochemically functionalized multilayered nanostructures onto electrodes in a controllable manner through layer-by-layer (LBL) chemistry. Methylene green (MG) and positively charged methylimidazolium-functionalized multiwalled carbon nanotubes (MWNTs) were used as examples of electroactive species and electrochemically useful components for the assembly, respectively. By using graphene as the spacer, the multilayered nanostructures of graphene/MG and graphene/MWNT could be readily formed onto electrodes with the LBL method on the basis of the electrostatic and/or π-π interaction(s) between graphene and the electrochemically useful components. Scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), and cyclic voltammetry (CV) were used to characterize the assembly processes, and the results revealed that nanostructure assembly was uniform and effective with graphene as the spacer. Electrochemical studies demonstrate that the assembled nanostructures possess excellent electrochemical properties and electrocatalytic activity toward the oxidation of NADH and could thus be used as electronic transducers for bioelectronic devices. This potential was further demonstrated by using an alcohol dehydrogenase-based electrochemical biosensor and glucose dehydrogenase-based glucose/O(2) biofuel cell as typical examples. This study offers a simple route to the controllable formation of graphene-based electrochemically functionalized nanostructures that can be used for the development of molecular bioelectronic devices such as biosensors and biofuel cells.