Low potential detection of NADH based on Fe₃O₄ nanoparticles/multiwalled carbon nanotubes composite: fabrication of integrated dehydrogenase-based lactate biosensor

Fe(3)O(4) magnetic nanoparticles were in situ loaded on the surface of multiwalled carbon nanotubes (MWCNTs) by a simple coprecipitation procedure. The resulting Fe(3)O(4)/MWCNTs nanocomposite brings new capabilities for electrochemical sensing by combining the advantages of Fe(3)O(4) magnetic nanoparticles and MWCNTs. It was found that Fe(3)O(4) has redox properties similar to those of frequently used mediators used for electron transfer between NADH and electrode. The cyclic voltammetric results indicated the ability of Fe(3)O(4)/MWCNTs modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.0 mV vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 650 mV compared with the bare GC electrode. The catalytic oxidation current allows the stable and selective amperometric detection of NADH at an applied potential of 0.0 mV (Ag/AgCl) with a detection limit of 0.3 μM and linear response up to 300 μM. This modified electrode can be used as an efficient transducer in the design of biosensors based on coupled dehydrogenase enzymes. Lactate dehydrogenase (LDH) and NAD(+) were subsequently immobilized onto the Fe(3)O(4)/MWCNTs nanocomposite film by covalent bond formation between the amine groups of enzyme or NAD(+) and the carboxylic acid groups of the Fe(3)O(4)/MWCNT film. Differential pulse voltammetric detection of lactate on Fe(3)O(4)/MWCNT/LDH/NAD(+) modified GC electrode gives linear responses over the concentration range of 50-500 μM with the detection limit of 5 μM and sensitivity of 7.67 μA mM(-1). Furthermore, the applicability of the sensor for the analysis of lactate concentration in human serum samples has been successfully demonstrated.     

D-fructose detection based on the direct heterogeneous electron transfer reaction of fructose dehydrogenase adsorbed onto multi-walled carbon nanotubes synthesized on platinum electrode

Multi-walled carbon nanotubes (MWCNTs) were synthesized on platinum plate electrodes by the chemical vapor deposition (CVD) method. From the results of X-ray photoelectron spectroscopy and voltammetric investigation, the iron nanoparticles used as a catalyst for the MWCNT synthesis were enclosed with MWCNTs. The MWCNTs synthesized on the Pt plate (MWCNTs/Pt) electrode were immediately immersed into solutions of d-fructose dehydrogenase (FDH) to immobilize the enzyme onto the MWCNTs/Pt electrode surfaces. After the FDH was immobilized onto the MWCNTs/Pt electrode, a well-defined catalytic oxidation current based on FDH was observed from ca. -0.15V (versus Ag/AgCl/sat'd KCl), which was close to the redox potential of heme c as a prosthetic group of FDH. From an analysis of a plot of the catalytic current versus substrate, the calibration range for the fructose concentration was up to ca. 40mmoldm(-3), and the apparent Michaelis-Menten constant was evaluated to be 11+/-1mmoldm(-3).     

Direct electrochemistry and electrocatalytic activity of catalase incorporated onto multiwall carbon nanotubes-modified glassy carbon electrode

The direct voltammetry and electrocatalytic properties of catalase, which was adsorbed on the surface of multiwall carbon nanotubes (MWCNTs), was investigated. A pair of well-defined and nearly reversible cyclic voltammetry peaks for Fe(III)/Fe(II) redox couple of catalase adsorbed on the surface of MWCNTs at approximately -0.05 V versus reference electrode in pH 6.5 buffer solution, indicating the direct electron transfer between catalase and electrode. The surface coverage of catalase immobilized on MWCNTs glassy carbon electrode was approximately 2.4x10(-10) molcm-2. The transfer coefficient (alpha) was calculated to be 0.4, and the heterogeneous electron transfer rate constant was 80 s-1 in pH 7, indicating great facilitation of the electron transfer between catalase and MWCNTs adsorbed on the electrode surface. The formal potential of catalase Fe(III)/Fe(II) couple in MWCNTs film had a linear relationship with pH values between 2 and 11 with a slope of 58 mV/pH, showing that the electron transfer is accompanied by single proton transportation. Catalase adsorbed on MWCNTs exhibits a remarkable electrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The value for calculated Michaelis-Menten constant (1.70 mM) was high, indicating the potential applicability of the films as a new type of reagentless biosensor based on the direct electrochemistry of the catalase enzyme.     

Biocompatible poly(L-lactide)/MWCNT nanocomposites: morphological characterization, electrical properties, and stem cell interaction

The promising perspectives of PLLA-based nanostructured biomaterials and their relevance in tissue engineering are reported. Nanocomposites based on PLLA and MWCNTs are developed with an MWCNT content ranging from 0 to 3 wt%. The electrical properties show a percolation threshold within a range of 0.21-0.33 wt% MWCNTs, and the conductivity increases by six orders of magnitude. The surface structure shows changes with the carbon nanotube concentration. The functional role of MWCNTs incorporation in terms of interactions with adult stem cells suggests that PLLA/MWCNT nanocomposites are suitable substrates for primary stem cell culture.     

Multi-Wall Carbon Nanotubes Effects on Plant Seedlings Growth and Cadmium/Lead Uptake In Vitro

The effects of multi-wall carbon nanotubes (MWCNTs) on plant growth and Cd/Pb accumulation was investigated on seedlings of three plant species including Brassica napus L., Helianthus annus L. and Cannabis sativa L. The experiment consisted of MWCNTs on three concentration levels (0, 10, 50 mg/L) and 200 μM CdCl₂ or 500 μM Pb(NO₃)₂. MWCNTs application effectively improved root and shoot growth inhibited by Cd and Pb salts. In B. napus, total chlorophyll (Chl) content increased by both MWCNTs 10 and 50 mg/L exposure under cadmium or lead stress. MWCNT 10 mg/L mitigated the deleterious effects of Cd ions on total chlorophyll content of H. annus and C. sativa. Wherease higher concentration of MWCNTs decreased Chl content under either Cd or Pb treatments on sunflower seedlings. MWCNT10 effectivly raised cadmium accumulation in seedlings of all three species. MWCNT10 and 50 mg/L also caused higher Pb accumulation in canola and cannabis seedlings, respectively. Based on the results, it seems that the effects of MWCNTs on growth parameters and heavy metal accumulation in plant seedlings is strongly depends on heavy metal type, MWCNTs concentration and plant species.     

A highly efficient buckypaper-based electrode material for mediatorless laccase-catalyzed dioxygen reduction

The redox enzyme laccase from Trametes versicolor efficiently catalyzes the oxygen reduction reaction (ORR) in mediatorless biofuel cell cathodes when adsorbed onto multi-walled carbon nanotubes (MWCNTs). In this work we demonstrate that the fabrication of MWCNTs in form of buckypaper (BP) results in an excellent electrode material for laccase-catalyzed cathodes. BPs are mechanically stable, self-entangling mats with high dispersion of MWCNTs resulting in easy to handle homogeneous layers with highly mesoporous structures and excellent electrical conductivities. All biocathodes have been electrochemically investigated in oxygen-saturated buffer at pH 5 by galvanostatic polarization and potentiodynamic linear sweep voltammetry. Both methods confirm an efficient direct interaction of laccase with BP with a high open circuit potential of 0.882 V vs. normal hydrogen electrode (NHE). The high oxygen reduction performance leads to high current densities of 422±71 μA cm(-2) at a typical cathode potential of 0.744 V vs. NHE. When the current density is normalized to the mass of the electrode material (mass activity), the BP-based film electrodes exhibit a 68-fold higher current density at 0.744 V vs. NHE than electrodes fabricated from the same MWCNTs in a non-dispersed agglomerated form as packed electrodes. This clearly shows that MWCNTs can act more efficiently as cathode when prepared in form of BP. This can be attributed to reduced diffusional mass transfer limitations and enhanced electrical conductivity. BP is thus a very promising material for the construction of mediatorless laccase cathodes for ORR in biofuel cells. In addition we demonstrated that these electrodes exhibit a high tolerance towards glucose, the most common bioanode fuel.     

Application of a novel plasma-induced CD/MWCNT/iron oxide composite in zinc decontamination

Herein, β-cyclodextrin (β-CD) was grafted onto magnetic MWCNT/iron oxide particles by using low temperature plasma-induced technique to synthesize a novel nanocomposite. The prepared composite (denoted as CD/MWCNT/iron oxide) exhibited high magnetic property (saturation magnetization M(s)=37.8emu/g) and good dispersion property in aqueous solution. Batch experiments were conducted to evaluate the application potential of CD/MWCNT/iron oxide in the decontamination of Zn(II) from aqueous solutions. The sorption amount of Zn(II) on CD/MWCNT/iron oxide was higher than that of Zn(II) on MWCNT/iron oxides and oxidized MWCNTs, indicating that the grafted β-CD could enhance the sorption capacity of CD/MWCNT/iron oxide composite toward Zn(II) by providing multiple hydroxyl functional groups. Due to its high magnetic, CD/MWCNT/iron oxide could be easily separated from aqueous solution with an external magnetic field. Regeneration studies suggested that CD/MWCNT/iron oxide can support long term use as a cost-effective material in sewage treatment with minimum replacement costs.     

Significantly Enhanced Actuation Performance of IPMC by Surfactant-Assisted Processable MWCNT/Nafion Composite

The performance of Ionic Polymer Metal Composite (IPMC) actuator was significantly enhanced by incorporating surfactant-assisted processable Multi-Walled Carbon Nanotubes (MWCNTs) into a Nafion solution. Cationic surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) was employed to disperse MWCNTs in the Nafion matrix, forming a homogeneous and stable dispersion of nanotubes. The processing did not involve any strong acid treatment and thus effectively preserved the excellent electronic properties associated with MWCNT. The as-obtained MWCNT/Nafion-IPMC actuator was tested in terms of conductivity, bulk and surface morphology, blocking force and electric current. It was shown that the blocking force and the current of the new IPMC are 2.4 times and 1.67 times higher compared with a pure Nafion-based IPMC. Moreover, the MWCNT/IPMC performance is much better than previously reported Nafion-IPMC doped by acid-treated MWCNT. Such significantly improved performance should be attributed to the improvement of electrical property associated with the addition of MWCNTs without acid treatment.     

A third-generation hydrogen peroxide biosensor based on horseradish peroxidase immobilized in a tetrathiafulvalene-tetracyanoquinodimethane/multiwalled carbon nanotubes film

A new third-generation biosensor for H(2)O(2) assay was developed on the basis of the immobilization of horseradish peroxidase (HRP) in a nanocomposite film of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ)/multiwalled carbon nanotubes (MWCNTs) modified gold electrode. The prepared HRP/TTF-TCNQ/MWCNTs/Au electrode was used for the bioelectrocatalytic reduction of H(2)O(2), with a linear range from 0.005 to 1.05mM and a detection limit of 0.5muM for amperometric sensing of H(2)O(2). In addition, a novel method on the basis of electrochemical quartz crystal microbalance (EQCM) measurements was proposed to determine the effective enzymatic specific activity (ESA) of the immobilized HRP for the first time, and the ESA was found to be greater at the TTF-TCNQ/MWCNTs/Au electrode than that at the MWCNTs/Au or TTF-TCNQ/Au electrode, indicating that the TTF-TCNQ/MWCNTs film is a good HRP-immobilization matrix to achieve the direct electron transfer between the enzyme and the electrode.     

Incorporation of Indium Tin Oxide Nanoparticles in PEMFC Electrodes

Carbon materials suffer from corrosion at the cathode of polymer electrolyte membrane fuel cells (PEMFCs). In the presence of water, carbon support materials are oxidized to carbon dioxide even at low potentials. Hence, nowadays it is very fashionable to look for alternative support materials, like oxides or conductive polymers. To gain the maximum performance for a new material one should also consider an appropriate electrode structure. This study shows the results for the incorporation of nanosized alternative support materials into advanced electrode architectures. Commercially available indium tin oxide (ITO) nanoparticles (<50 nm) are used as support for Pt nanoparticles in combination with Nafion‐coated multi‐walled carbon nanotubes (MWCNTs) on the cathode side of a PEMFC. The MWCNTs promote a high electronic conductivity and help to form a porous network, which could accommodate the Pt/ITO nanoparticles. The microscopic investigations show a homogeneous electrode structure composed of Pt/ITO and MWCNT/Nafion multilayer. Single cell measurements show a maximum power density of 73 mW cm^?2 and a Pt utilization of 1468 mW mg_Pt^?1 for the cathode. The performance data and the Pt utilization are comparable to a standard Pt/carbon black electrode possessing the same Pt loading in the electrode. Beside this, it is shown for the first time that ITO serves as support material under real fuel cell conditions.     

In vitro comparative cytotoxic assessment of pristine and carboxylic functionalized multiwalled carbon nanotubes on LN18 cells

Multiwalled carbon nanotubes (MWCNTs) have been used in biomedical applications due to their ability to enter the cells. Carboxylic functionalization of MWCNT (MWCNT-COOH) is used to mitigate the toxicity of MWCNTs. Our study focuses on comparing the toxicity of MWCNT and MWCNT-COOH on the neuronal cells, LN18. Concentrations of 5, 10, 20, and 40 µg ml⁻¹ were used for the study, and cytotoxicity was determined at 0, 1, 3, 6, 12, 24, and 48 h of incubation. Cell viability was assessed by Trypan Blue, MTT, and Live dead cell assays, and the oxidative stress produced was determined by reactive oxygen species (ROS) and Lipid peroxidation assays. MWCNT-COOH showed higher cell viability than MWCNT for 20 and 40 µg ml⁻¹ at 24 and 48 h. This was also visually observed in the live dead cell imaging. However, at 48 h, the morphology of the cells appeared more stretched for all the concentrations of MWCNT and MWCNT-COOH in comparison to the control. A significant amount of ROS production can also be observed at the same concentration and time. Viability and oxidative stress results together revealed that MWCNT-COOH is less toxic when compared to MWCNT at longer incubation periods and higher concentrations. However, otherwise, the effect of both are comparable. A concentration of 5–10 µg ml⁻¹ is ideal while using MWCNT and MWCNT-COOH as the toxicity is negligible. These findings can further be extended to various functionalizations of MWCNT for wider applications.     

Anionic complexes of MWCNT with supergiant cyanobacterial polyanions

Multi‐walled carbon nanotubes (MWCNTs) were well dispersed in an aqueous solution of the cyanobacterial polysaccharide, sacran, with an ultra‐high molecular weight >10 million g/mol. MWCNTs powder was put into aqueous solutions of various polysaccharides including sacran and was dispersed under sonication. As a result of the turbidity measurement of the supernatant, it was found that sacran showed the highest MWCNT‐dispersion efficiency of all the polysaccharides used here. Cryogenic transmission electron microscopic (Cryo‐TEM) studies directly demonstrated the existence of MWCNTs in the supernatant, and high‐resolution TEM observation revealed that MWCNTs covered by sacran chains made their efficient dispersion in water. Raman spectroscopy demonstrated the existence of MWCNT in dried sample from supernatant and the interaction between MWCNT and sacran. The ζ‐potential measurement of the dispersion indicated the negative surface charges of the sacran/MWCNT complexes. Then the MWCNT complexes were able to fabricate by ionic interaction; electrophoresis of the anionic complex formed the sacran/MWCNT gels on the anode while the droplet of sacran/MWCNT dispersion formed gel beads in the presence of the lanthanoid cations. © 2012 Wiley Periodicals, Inc.     

Multiwalled carbon nanotubes dispersed in carminic acid for the development of catalase based biosensor for selective amperometric determination of H(2)O(2) and iodate

We report the preparation of stable dispersion of multiwalled carbon nanotubes (MWCNTs) using carminic acid (CA) as a dispersing agent. The transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) results confirmed that MWCNT is well dispersed in CA aqueous solution and CA has been well adsorbed at MWCNT walls. Fourier transform infrared (FTIR) and UV-vis absorption spectra results also confirmed the adsorption of CA at MWCNT. To develop a highly selective amperometric biosensor for H(2)O(2) and iodate, the model enzyme catalase (CAT) was immobilized at CACNT modified glassy carbon electrode surface. The immobilized CAT exhibits well defined quasi reversible redox peaks at a formal potential (E°') of -0.559V in 0.05M pH 7 phosphate buffer solution (PBS). The proposed CAT/CACNT biosensor exhibits excellent amperometric response towards H(2)O(2) and iodate in the linear concentration range between 10μM to 3.2mM and 0.01-2.16mM. The sensitivity values are 287.98μAmM(-1)cm(-2) and 0.253mAmM(-1)cm(-2), respectively. Moreover, the developed CAT biosensor exhibits high affinity for H(2)O(2) and iodate with good selectivity.     

Immobilization of glucose oxidase on graphene oxide for highly sensitive biosensors

Glucose oxidase (GOx) was immobilized onto graphene oxide (GRO) via three different preparation methods: enzyme adsorption (EA), enzyme adsorption and crosslinking (EAC), and enzyme adsorption, precipitation and crosslinking (EAPC). EAPC formulations, prepared via enzyme precipitation with 60% ammonium sulfate, showed 1,980 and 1,630 times higher activity per weight of GRO than those of EA and EAC formulations, respectively. After 59 days at room temperature, EAPC maintained 88% of initial activity, while EA and EAC retained 42 and 45% of their initial activities, respectively. These results indicate that the steps of precipitation and crosslinking in the EAPC formulation are critical to achieve high enzyme loading and stability of EAPC. EA, EAC and EAPC were used to prepare enzyme electrodes for use as glucose biosensors. Optimized EAPC electrode showed 93- and 25-fold higher sensitivity than EA and EAC, respectively. To further increase the sensitivity of EAPC electrode, multi-walled carbon nanotubes (MWCNTs) were mixed with EAPC for the preparation of enzyme electrode. Surprisingly, the EAPC electrode with additional 99.5 wt% MWCNTs showed 7,800-fold higher sensitivity than the EAPC electrode without MWCNT addition. Immobilization and stabilization of enzymes on GRO via the EAPC approach can be used for the development of highly sensitive biosensors as well as to achieve high enzyme loading and stability.     

微丝电极阵列的参考电极内置与外置的对比研究*

目的: 通过对比内置和外置参考电极的微丝电极阵列在记录大鼠脑神经元放电过程中的优缺点,优化微丝电极阵列的制作与埋置,为多通道电生理实时记录系统提供更加实惠、优异的媒介工具。方法: 采用镍铬合金丝、电路板、电极引脚和地线(银线)制作16通道的微丝电极阵列,通过内置(参考电极与电极阵列并列排布)或外置(参考电极与地线分别焊接在电极一侧的两端)微丝电极阵列的参考电极,观察对比两种电极在记录大鼠ACC脑区神经元放电中的区别。实验大鼠分为内置组(8只)和外置组(9只),检测指标有信噪比(n=8)、放电幅度(n=380)和放电频率(n=54)。结果: 内置与外置参考电极的微丝电极阵列均可顺利记录出大鼠ACC脑区神经元的电信号;与外置组相比,内置组的神经元电信号具有信噪比高(P＜0.05)、背景信号幅度小、受噪音干扰小,和放电幅度大(P＜0.05)的优点;锋电位放电频率没有显著差异(P＞0.05)。结论: 在记录大鼠ACC脑区神经元电活动时,内置参考电极的微丝电极阵列记录到更高信噪比、更大放电幅度的电信号,为多通道电生理技术提供更加可靠的工具。     

Vitamin B(12) incorporated with multiwalled carbon nanotube composite film for the determination of hydrazine

Electrochemically active composite film containing multiwalled carbon nanotubes (MWCNTs) and vitamin B₁₂ was synthesized on glassy carbon, gold, and indium tin oxide electrodes by the potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT–B₁₂) modified electrode mediates vitamin B₁₂’s redox reaction, whereas vitamin B₁₂’s redox reaction does not occur at bare electrode. The electrochemical impedance spectroscopy studies reveal that MWCNTs present in MWCNT–B₁₂ film enhance electron shuttling between the reactant and electrode surface. The surface morphology of bare electrode, MWCNT film. and MWCNT–B₁₂ composite film was studied using atomic force microscopy, which reveals vitamin B₁₂ incorporated with MWCNTs. The MWCNT–B₁₂ composite film exhibits promising enhanced electrocatalysis toward hydrazine. The electrocatalysis response of hydrazine at MWCNT film and MWCNT–B₁₂ composite film was measured using cyclic voltammetry and amperometric current–time (i–t) curve techniques. The linear concentration range of hydrazine obtained at MWCNT–B₁₂ composite film using the i–t curve technique is 2.0 μM–1.95 mM. Similarly, the sensitivity of MWCNT–B₁₂ composite film for hydrazine determination using the i–t curve technique is 1.32 mA mM⁻¹ cm⁻², and the hydrazine’s limit of detection at MWCNT–B₁₂ composite film is 0.7 μM.     

Synergetic Protective Effect of the Ultralight MWCNTs/NCQDs Modified Separator for Highly Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are highly attractive due to their high energy density, potentially low cost, and environmental compatibility. However, their commercialization has been greatly hindered by their poor cycle life and severe self‐discharge, which can be attributed to the polysulfides dissolution. To overcome these issues, much effort has been devoted to engineering the electrode structure and composition to improve the performance which is often expensive and laborious. In this study, an ultralight multiwall carbon nanotube/N‐doped carbon quantum dot (MWCNT/NCQD)‐coated separator is first designed, which is cost effective and facile. The MWCNTs/NCQDs‐coated separator is then applied in Li–S batteries. The MWCNTs/NCQDs coating provides a physical shield against polysulfide shuttling and chemical adsorption of polysulfides by MWCNTs and NCQDs. The synergetic effect of MWCNTs and NCQDs enables the production of Li–S cell with a relative high initial discharge capacity of 1330.8 mA h g^?1 and excellent cyclic performance with a corresponding capacity fade rate of as low as 0.05% per cycle at 0.5 C over 1000 cycles. Excellent rate capability and anti‐self‐discharge behavior are also displayed. The design of MWCNTs/NCQDs‐coated separator is a viable approach for successfully developing practical Li–S batteries.     

A mediatorless biosensor for putrescine using multiwalled carbon nanotubes

Poly(diallyldimethylammonium) chloride, having a capability of dispersing multiwalled carbon nanotubes (MWCNTs), permits the modification of electrode surfaces. Together with putrescine oxidase, a MWCNT modified glassy carbon electrode was constructed for the development of a mediatorless putrescine biosensor. Nanoscale "dendrites" of MWCNTs were reasoned to form a network, projecting outward from the electrode surface acting like bundled ultra-microelectrodes, thereby permitting access to the active site and facilitating direct electron transfer to the immobilized enzyme. Our biosensor was capable of efficiently monitoring the direct electroactivity of putrescine oxidase at the electrode surface. Direct electron transfer permits the detection of putrescine at negative potentials, circumventing the interference of endogenous ascorbic and uric acids, which often complicate the analysis of important compounds in plasma. Compared with the most common interfering species, such as spermine, spermidine, cadaverine, and histamine, a detection limit of 5 microM and a response 20 times greater were found for putrescine. Tests performed on plasma of cancerous mice demonstrated that the detection of putrescine could be carried out very quickly on mammalian plasma without previous purification.     

Bimetallic PtM (M=Pd, Ir) nanoparticle decorated multi-walled carbon nanotube enzyme-free, mediator-less amperometric sensor for H₂O₂

A new highly catalytic and intensely sensitive amperometric sensor based on PtM (where M=Pd, Ir) bimetallic nanoparticles (NPs) for the rapid and accurate estimation of hydrogen peroxide (H(2)O(2)) by electrooxidation in physiological conditions is reported. PtPd and PtIr NPs-decorated multiwalled carbon nanotube nanocatalysts (PtM/MWCNTs) were prepared by a modified Watanabe method, and were characterized by XRD, TEM, ICP, and XAS. The sensors were constructed by immobilizing PtM/MWCNTs nanocatalysts in a Nafion film on a glassy carbon electrode. Both PtPd/MWCNTs and PtIr/MWCNTs assemblies catalyzed the electrochemical oxidation of H(2)O(2). Cyclic voltammetry characterization measurements revealed that both the PtM (M=Pd, Ir)/MWCNTs/GCE possessed similar electrochemical surface areas (～0.55 cm(2)), and electron transfer rate constants (～1.23 × 10(-3)cms(-1)); however, the PtPd sensor showed a better performance in H(2)O(2) sensing than did the PtIr counterpart. Explanations were sought from XAS measurements to explain the reasons for differences in sensor activity. When applied to the electrochemical detection of H(2)O(2), the PtPd/MWCNTs/GC electrode exhibited a low detection limit of 1.2 μM with a wide linear range of 2.5-125 μM (R(2)=0.9996). A low working potential (0V (SCE)), fast amperometric response (<5s), and high sensitivity (414.8 μA mM(-1)cm(-2)) were achieved at the PtPd/MWCNTs/GC electrode. In addition, the PtPd/MWCNTs nanocatalyst sensor electrode also exhibited excellent reproducibility and stability. Along with these attractive features, the sensor electrode also displayed very high specificity to H(2)O(2) with complete elimination of interference from UA, AA, AAP and glucose.     

Dual functional nisin-multi-walled carbon nanotubes coated filters for bacterial capture and inactivation

Background

Removal of pathogens from water is one way to prevent waterborne illness. In this paper, we developed dual functional carbon nanotube (CNT) modified filters for bacterial capture and inactivation, utilizing multi-walled CNTs (MWCNTs) to coat on commercially available filters and making use of the exceptional adsorption property of CNTs to adsorb a natural antimicrobial peptide-nisin on it. Two types of MWCNTs with different outer layer diameters were used (MWCNTs1: <8 nm in diameter; MWCNTs2: 10–20 nm in diameter).

Results

The thickness of MWCNT layers, surface morphology, and surface hydrophobicity of both types of MWCNT coated filters were characterized. The MWCNT coating on filters significantly increased the surface hydrophobicity. The absorption of nisin and the capture of bacterial pathogens were correlated with increased surface hydrophobicity. The MWCNTs1 and MWCNTs2 filters with 1.5 mg MWCNTs loading captured 2.44 and 3.88 log of cells, respectively, from aqueous solutions containing a total of ~10⁶ CFU/mL cells. Nisin deposit at the amount of 0.5 mg on the surfaces of MWCNT filters significantly reduced the viability of captured B. anthracis cells by 95.71–97.19 %, and inhibited the metabolic activities of the captured cells by approximately 98.3 %.

Conclusions

The results demonstrated that the MWCNT-nisin filters achieved dual functions in bacterial pathogen capture and inhibition in one single filtration step, which is potentially applicable in removing undesired microorganisms from water sources and inhibiting captured Gram positive bacteria activities.