Composite film of carbon nanotubes and chitosan for preparation of amperometric hydrogen peroxide biosensor

A new amperometric biosensor for hydrogen peroxide was developed based on cross-linking horseradish peroxidase (HRP) by glutaraldehyde with multiwall carbon nanotubes/chitosan (MWNTs/chitosan) composite film coated on a glassy carbon electrode. MWNTs were firstly dissolved in a chitosan solution. Then the morphology of MWNTs/chitosan composite film was characterized by field-emission scanning electron microscopy. The results showed that MWNTs were well soluble in chitosan and robust films could be formed on the surface. HRP was cross-linked by glutaraldehyde with MWNTs/chitosan film to prepare a hydrogen peroxide biosensor. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for H₂O₂ in the absence of a mediator. The linear range of detection towards H₂O₂ (applied potential: −0.2 V) was from 1.67 × 10⁻⁵ to 7.40 × 10⁻⁴ M with correction coefficient of 0.998. The biosensor had good repeatability and stability for the determination of H₂O₂. There were no interferences from ascorbic acid, glucose, citrate acid and lactic acid.     

Synergistic degradation to prepare oligochitosan by γ-irradiation of chitosan solution in the presence of hydrogen peroxide

Synergistic degradation of chitosan by γ-irradiation of chitosan solution (3%) in the presence of hydrogen peroxide (0.25%, 0.5% and 1%) was investigated. The efficiency of the degradation process was demonstrated by gel permeation chromatography (GPC) analysis of the average molecular weight of degraded chitosan (oligochitosan). Structures of resultant oligochitosan were characterized by Fourier-transform infrared spectra (FT-IR) and X-ray diffraction (XRD). Results showed that oligochitosan with Mw from 5000 to 10,000 could be efficiently prepared by γ-irradiation of chitosan solution containing a small amount of hydrogen peroxide at low dose less than 10 kGy. There was almost no significant change in the main chain structure of oligochitosan; however, the obtained oligochitosans lost about 10% of amino groups and the formation of carboxyl groups could not be specified by FT-IR spectra. The morphology state of oligochitosan was essentially amorphous, which differs from that of original chitosan. The combined γ ray/H₂O₂ method is significantly efficient for scale-up manufacture of oligochitosan.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

Influence of microwave heating on fluoride, chloride, nitrate and sulfate concentrations in water

This paper describes a study about the influence of microwave radiation using closed vessels on fluoride, chloride, nitrate and sulfate concentrations in aqueous media. The experiments were processed by heating water using PFA vessels and a microwave cavity oven, determining the anions by ion chromatography. The influence of the exposure time, the atmospheric composition, the kind of heating (water bath or microwave radiation) and the possible formation of hydrogen peroxide were investigated. The limits of quantification for fluoride, chloride, nitrate and sulfate were respectively of 0.17, 0.15, 0.55 and 0.57 μg L⁻¹, and precision, expressed as RSD, was <4% for all considered anions. The hydrogen peroxide was quantified by spectrophotometry, and the limit of quantification and precision were 24 μg L⁻¹ and <5% (n = 10), respectively. The results demonstrate a significant increase in the anion concentration levels (between 63 and 89%) when microwave heating was used in comparison with heating by water bath. In addition, these changes observed can be mainly attributed to the species transfers, either between gaseous (atmospheric gases) and liquid (water) phases for nitrate, or between vessels walls and water for fluoride, chloride and sulfate. Additionally, hydrogen peroxide concentration higher than 45 μg L⁻¹ was determined when water was exposed to microwave radiation.     

Localized surface plasmon resonance sensor for simultaneous kinetic determination of peroxyacetic acid and hydrogen peroxide

A new sensor for simultaneous determination of peroxyacetic acid and hydrogen peroxide using silver nanoparticles (Ag-NPs) as a chromogenic reagent is introduced. The silver nanoparticles have the catalytic ability for the decomposition of peroxyacetic acid and hydrogen peroxide; then the decomposition of them induces the degradation of silver nanoparticles. Hence, a remarkable change in the localized surface plasmon resonance absorbance strength could be observed. Spectra-kinetic approach and artificial neural network was applied for the simultaneous determination of peroxyacetic acid and hydrogen peroxide. Linear calibration graphs were obtained in the concentration range of (8.20 × 10⁻⁵ to 2.00 × 10⁻³ mol L⁻¹) for peroxyacetic acid and (2.00 × 10⁻⁵ to 4.80 × 10⁻³ mol L⁻¹) for hydrogen peroxide. The analytical performance of this sensor has been evaluated for the detection of simultaneous determination of peroxyacetic acid and hydrogen peroxide in real samples.     

Effect of gamma radiation on dilute aqueous solutions and thin films of N-succinyl chitosan

N-Succinyl chitosan (N-SC) products with various degrees of substitution were synthesized by a direct reaction between chitosan and succinic anhydride. The susceptibility of the as-synthesized polymers to degradation upon their exposure to γ-ray radiation was investigated. The results were compared with the as-received chitosan. The size exclusion chromatographic results showed that chitosan and N-SC products in their dilute aqueous solution state were more subservient to degradation by γ-ray radiation than in their solid film state, despite the much less exposure to the radiation (i.e., 5-30 kGy for the solutions versus 20-100 kGy for the films). Increasing the radiation dose resulted in the rather monotonous decrease in the molecular weights of the polymers. Structural analyses of the irradiated polymers by Fourier-transformed infrared spectroscopy (FT-IR) and UV-visible spectrophotometry indicated the increase in the amount of carbonyl groups with the radiation dose. The formation of the carbonyl groups suggested that the radiolysis of chitosan and N-SC products occurred at the glycosidic linkages. In addition, FT-IR, elemental analysis and proton nuclear magnetic resonance spectroscopy (¹H NMR) results suggested that γ-ray radiation affected both the N-acetyl and N-substituted groups on the polymer chains.     

Effectiveness of radiation processing in elimination of Campylobacter from poultry meat

Campylobacter, a common poultry intestine commensal, is a well known cause of human gastric illnesses across the globe. Consumption of contaminated poultry meat is a major cause of Campylobacter related infections. In the present study, radiation sensitivity of indigenous strains of C. jejuni and C. coli isolated from poultry was evaluated. The decimal reduction dose (D₁₀) values of different Campylobacter isolates at 0-4 °C in saline and blood broth were in the range of 0.120-0.210 kGy and 0.170-0.234 kGy, respectively. D₁₀ values in chicken meat homogenate for Campylobacter were in the range of 0.110-0.190 kGy. Chicken meat samples were inoculated with C. jejuni and exposed to gamma radiation to study the effectiveness of radiation treatment in elimination of Campylobacter. Radiation treatment with a dose of 1 kGy could achieve complete elimination of 10⁵ CFU of Campylobacter/g in poultry meat samples. No recovery of Campylobacter was observed, even after enrichment and selective plating in 1 kGy treated chicken meat samples stored at 4 °C up to 7 days. Present study shows that irradiation of poultry meat with 1 kGy can ensure safety of poultry meat.     

Determination of hydrogen peroxide by using a flow injection system with immobilized peroxidase and long pathlength capillary spectrophotometry

The development of a highly sensitive method for the determination of nanomolar concentrations of hydrogen peroxide in the liquid phase is described. This paper demonstrates for the first time a flow injection analysis (FIA) system with immobilized enzyme reactor combined with a total internal reflective cell (a liquid waveguide capillary cell (LWCC)) and spectrophotometric detection, for the development of an improved procedure for the determination of hydrogen peroxide. Moreover, the newly synthesized 4-aminopyrazolone derivative, 4-amino-5-(p-aminophenyl)-1-methyl-2-phenyl-pyrazol-3-one (DAP), is used as a color coupler in its oxidative condensation with the sodium salt of N-ethyl-N-sulphopropylaniline sodium salt (ALPS) which acts as a hydrogen donor. Immobilization of peroxidase is achieved by coupling the periodate-treated enzyme to aminopropyl controlled-pore glass (CPG) beads. The determination of hydrogen peroxide is carried out in a 0.1 M phosphate buffer and the product is monitored at 590 nm with a charge-coupled device (CCD) detector equipped with fiber optics in a fully computerized system. The interference of different species, mainly ionic, was investigated.The method permits detection down to 4 nmol l⁻¹ hydrogen peroxide (signal-to-noise ratio=3). A linear calibration graph was obtained over the range 20-700 nmol l⁻¹. The relative standard deviation (R.S.D.) at 300 nmol l⁻¹ H₂O₂ is 1.7% (n=7). The method was successfully applied for the determination of hydrogen peroxide in samples from a vat-cleaning process.     

Effects of microstructure of carbon nanofibers for amperometric detection of hydrogen peroxide

Carbon nanofibers (CNFs) with three microstructures, including platelet-carbon nanofibers (PCNFs), fish-bone-carbon nanofibers (FCNFs), and tube-carbon nanofibers (TCNFs), were synthesized, characterized, and evaluated for electrochemical sensing of hydrogen peroxide. The CNFs studied here show microstructures with various stacked morphologies. The sizes and graphite-layer ordering of the CNFs can be well controlled. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of hydrogen peroxide. Sensors based on PCNFs/GC, FCNFs/GC, and TCNFs/GC were used in the amperometric detection of H₂O₂ in solution by applying a potential of +0.65 V versus Ag/AgCl at the working electrode. The highest electrocatalytic performance was observed for PCNFs/GC among the three types of hydrogen peroxide sensors. The amperometric response of PCNFs/GC retained over 90% of the initial current of the first day up to 21 days. The linear range is from 1.80 × 10⁻⁴ to 2.62 × 10⁻³ M with a correlation coefficient larger than 0.999 and with a detection limit of 4.0 μM H₂O₂ (S/N = 3). The relative standard deviation for detecting 1.80 × 10⁻⁴ M H₂O₂ (N = 8) is 2.1% with an average response of 0.64 μA. The significant diversity of electrocatalytic activity of the CNFs toward the oxidation of hydrogen peroxide may result from the difference of morphologies, textural properties, and crystalline structures.     

Polyphosphonate induced coacervation of chitosan: Encapsulation of proteins/enzymes and their biosensing

Based on the polyphosphonate-assisted coacervation of chitosan, a simple and versatile procedure for the encapsulation of proteins/enzymes in chitosan–carbon nanotubes (CNTs) composites matrix was developed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrum (EDS) mapping demonstrated the hemoglobin (Hb) uniformly distributed into chitosan–CNTs composites matrix. Raman measurements indicated the CNTs in composites matrix retained the electronic and structural integrities of the pristine CNTs. Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) and circular dichroism (CD) spectroscopy displayed the encapsulated Hb preserved their near-native structure, indicating the polyphosphonate–chitosan–CNTs composites possessed excellent biocompatibility for the encapsulation of proteins/enzymes. Electrochemical measurements indicated the encapsulated Hb could directly exchange electron with the substrate electrode. Moreover, the modified electrode showed excellent bioelectrocatalytic activity for the reduction of hydrogen peroxide. Under optimum experimental conditions, the fabricated electrochemical sensor displayed the fast response (less than 3 s), wide linear range (7.0 × 10⁻⁷ to 2.0 × 10⁻³ M) and low detection limit (4.0 × 10⁻⁷ M) for the determination of hydrogen peroxide. This newly developed protocol was simple and mild and would certainly find extensive applications in biocatalysis, biosensors, bioelectronics and biofuel cells.     

Thermal, mechanical and electrical properties on the styrene-grafted and subsequently sulfonated FEP film induced by electron beam

This paper examined the mechanical and electrical properties of poly(tetrafluoroethylene-co-hexafluoropropylene: FEP) film modified by electron beam (EB). The simultaneous irradiation method with EB was adopted for the grafting of styrene and subsequent sulfonation onto FEP film. The thermal and mechanical characteristics of the irradiated FEP film, and also those of the grafted and sulfonated FEP films, were investigated by TGA, FT-IR spectrometer, and Instron. The simultaneous irradiation with EB facilitated the homogeneous grafting, as well as a high degree of grafting with a maximum value of around 60%, thereby allowing accurate control of the degree of grafting at doses ranging from 10 to 100 kGy.The grafting or sulfonation decreased the thermal stability of FEP, whereas it considerably increased its mechanical properties. The high radiation resistance of virgin FEP up to a dose of 100 kGy enabled the sulfonation of FEP film to considerably reinforce its polymeric structures except of 10 kGy, thereby increasing its tensile strength at 30 kGy by two-fold compared to that of the virgin FEP film. The ion conductivity (IC) and ion-exchange capacity (IEC) values of the FEP membrane (125 μm thick), which were dependant on the degree of grafting, were 0.25 S cm⁻¹ and 2.4 mmol/g, respectively, at 59.2% of the degree of grafting and were superior to those of the commercialized Nafion membrane (IC, 0.12 S cm⁻¹; IEC, 0.9-1.0 mmol/g).     

Dendrimer-rhodium nanoparticle modified glassy carbon electrode for amperometric detection of hydrogen peroxide

Metallic nanoparticles of rhodium were prepared by using the newly synthesized N,N-bis-succinamide-based dendrimer as stabilizers. The Rh nanoparticles were spherical shaped with a particle size of ∼2 nm. The dendrimer Rh-encapsulated nanoparticles (Rh-DENs) were immobilized on glassy carbon electrode (GCE) and their electrocatalytic activity towards hydrogen peroxide reduction was investigated using cyclic voltammetry and chronoamperometry. The Rh-DENs modified GCE showed excellent electrocatalytic activity for hydrogen peroxide reduction reactions. The steady-state cathodic current response of the modified electrode at −0.3 V (vs SCE) in phosphate buffer (pH 7.0) showed a linear response to hydrogen peroxide concentration ranging from 8 to 30 μM with a detection limit and sensitivity of 5 μM and 0.03103 × 10⁻⁶ A μM⁻¹, respectively.     

β−cyclodextrins-based inclusion complexes of CoFe2O4 magnetic nanoparticles as catalyst for the luminol chemiluminescence system and their applications in hydrogen peroxide detection

β−cyclodextrins (β−CD)-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts for chemiluminescence (CL) system using the luminol-hydrogen peroxide CL reaction as a model. The as-prepared inclusion complexes were characterized by XRD (X-ray diffraction), TGA (thermal gravimetric analysis) and FT-IR. The oxidation reaction between luminol and hydrogen peroxide in basic media initiated CL. The effect of β−CD-based inclusion complexes of CoFe₂O₄ magnetic nanoparticles and naked CoFe₂O₄ magnetic nanoparticles on the luminol-hydrogen peroxide CL system was investigated. It was found that inclusion complexes between β−CD and CoFe₂O₄ magnetic nanoparticles could greatly enhance the CL of the luminol-hydrogen peroxide system. Investigation on the kinetic curves and the chemiluminescence spectra of the luminol-hydrogen peroxide system demonstrates that addition of CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ MNPs does not produce a new luminophor of the chemiluminescent reaction. The luminophor for the CL system was still the excited-state 3-aminophthalate anions (3-APA*). The enhanced CL signals were thus ascribed to the possible catalysis from CoFe₂O₄ MNPs or inclusion complexes between β−CD and CoFe₂O₄ nanoparticles. The feasibility of employing the proposed system for hydrogen peroxide sensing was also investigated. Experimental results showed that the CL emission intensity was linear with hydrogen peroxide concentration in the range of 1.0 × 10⁻⁷ to 4.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁸ mol L⁻¹ under optimized conditions. The proposed method has been used to determine hydrogen peroxide in water samples successfully.     

An ultrasensitive iron(III)-complex based hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism

In this communication, the first nonelectrocatalysis-type hydrogen peroxide electrochemical sensor is reported. The electroactive iron(III) diethylenetriaminepentaacetic acid (DTPA-Fe^III) complex is immobilized on the cysteamine (cys) modified nanoporous gold (NPG) films by covalent method. The immobilized DTPA-Fe^III complex quickly communicates an electron with the electrode. Upon addition of hydrogen peroxide, however, hydrogen peroxide inhibits the direct electron transfer of the DTPA-Fe^III complex due to the generation of nonelectroactive DTPA-Fe^III–H₂O₂ complex. Based on quenching mechanism, the first hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism is developed. The novel hydrogen peroxide electrochemical sensor has the ultralow detection limit (1.0 × 10^–14 M) and wide linear range (1.0 × 10^–13 to 1.0 × 10^–8 M) with excellent reproducibility and stability.     

Fabrication of Pt/polypyrrole hybrid hollow microspheres and their application in electrochemical biosensing towards hydrogen peroxide

Pt/polypyrrole (PPy) hybrid hollow microspheres were successfully prepared by wet chemical method via Fe₃O₄ template and evaluated as electrocatalysts for the reduction of hydrogen peroxide. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), inductive coupled plasma emission spectrum (ICP) and Fourier-transform infrared spectra (FTIR) measurements. The results exhibited that ultra-high-density Pt nanoparticles (NPs) were well deposited on the PPy shell with the mean diameters of around 4.1 nm. Cyclic voltammetry (CV) results demonstrated that Pt/PPy hybrid hollow microspheres, as enzyme-less catalysts, exhibited good electrocatalytic activity towards the reduction of hydrogen peroxide in 0.1 M phosphate buffer solution (pH = 7.0). The composite had a fast response of less than 2 s with linear range of 1.0-8.0 mM and a relatively low detection limit of 1.2 μM (S/N = 3). The sensitivity of the sensor for H₂O₂ was 80.4 mA M⁻¹ cm⁻².     

Preparation of low-molecular-weight carboxymethyl chitosan and their superoxide anion scavenging activity

Low-molecular-weight carboxymethyl chitosans (CMCTSs) were prepared by oxidative degradation method involving hydrogen peroxide (H₂O₂) without or with microwave radiation. Viscosity determination and end group analysis were applied to measure molecular weights of CMCTSs. Effects of concentration of H₂O₂ and degradation time on molecular weights of CMCTSs were studied. The degradation process of CMCTSs will be accelerated with the aid of microwave radiation and degradation time may be reduced greatly. The superoxide anion scavenging activity of CMCTSs was evaluated by application of flow injection chemiluminescence technology. The 50% inhibition concentrations (IC₅₀s) of CMCTSs A, B, and C (1130, 2430 and 4350 Da) were 10.36, 17.57, and 23.38 mg/mL, respectively. The above results showed that CMCTSs with lower molecular weight had better superoxide anion scavenging activity.     

Study on polytetrafluoroethylene aqueous dispersion irradiated by gamma ray

Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20-200 kGy and the change in property of PTFE was characterized by differential scanning calorimetry (DSC), photon cross correlation spectroscopy (PCCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS). It was found that the mean particle size of PTFE reduces from 250 nm of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G(s), was determined to be 0.46 μmol/J.     

A novel electrochemical biosensor based on the hemin-graphene nano-sheets and gold nano-particles hybrid film for the analysis of hydrogen peroxide

Hydrogen peroxide is an important analyte in biochemical, industrial and environmental systems. Therefore, development of novel rapid and sensitive analytical methods is useful. In this work, a hemin-graphene nano-sheets (H-GNs)/gold nano-particles (AuNPs) electrochemical biosensor for the detection of hydrogen peroxide (H₂O₂) was researched and developed; it was constructed by consecutive, selective modification of the GCE electrode. Performance of the H-GNs/AuNPs/GCE was investigated by chronoamperometry, and AFM measurements suggested that the graphene flakes thickness was ∼1.3 nm and that of H-GNs was ∼1.8 nm, which ultimately indicated that each hemin layer was ∼0.25 nm. This biosensor exhibited significantly better electrocatalytic activity for the reduction of hydrogen peroxide in comparison with the simpler AuNPs/GCE and H-GNs/GCE; it also displayed a linear response for the reduction of H₂O₂ in the range of 0.3 μM to 1.8 mM with a detection limit of 0.11 μM (S N⁻¹ = 3), high sensitivity of 2774.8 μA mM⁻¹ cm⁻², and a rapid response, which reached 95% of the steady state condition within 5 s. In addition, the biosensor was unaffected by many interfering substances, and was stable over time. Thus, it was demonstrated that this biosensor was potentially suitable for H₂O₂ analysis in many types of sample.     

Determination of lead in vinegar by ICP-MS and GFAAS: evaluation of different sample preparation procedures

Lead concentrations of 59 different types of vinegars (15-307 μg l⁻¹ in balsamic vinegars and 36-50 μg l⁻¹ in wine vinegars) were determined using both inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS). Although the precision of direct analyses, following simple aqueous dilutions, with either instrumental method was poor; that precision, following nitric acid and/or hydrogen peroxide digestions, markedly improved with either instrument and the values obtained with the two instruments were in good agreement. The efficacy of different digestions, including (1) nitric acid using a heating block, with or without addition of hydrogen peroxide and (2) mixtures of nitric acid and hydrogen peroxide using ultraviolet (UV) photolysis, were then assessed. The latter procedure was found to be much faster and more efficient, but it was limited by the relatively high levels of contaminant lead in hydrogen peroxide. Consequently, it is recommended that lead concentrations in vinegar be measured following a nitric acid digestion and UV photolysis to oxidize all organic matter before ICP-MS or GFAAS analysis; and it is further recommend that the thermal settings for the latter analyses be adjusted to account for the apparent presence of relatively volatile organolead compounds in vinegar digests.     

Rapid determination of hydrogen peroxide in the wood pulp bleaching streams by a dual-wavelength spectroscopic method

This study has demonstrated a spectrophotometric method for residual hydrogen peroxide analysis in wood pulp bleaching streams. In an acidic medium, hydrogen peroxide can instantly associate with molybdate to form a peroxomolybdic acid complex that has an absorption peak at 330 nm. To avoid the spectral interference from excess molybdate ion, 350 nm is used for spectroscopic quantification. A linear relationship between the absorbance at 350 nm and peroxide concentration was found up to a peroxide concentration of ca. 0.2 mmol l⁻¹. It was discovered that 297 nm was an isosbestic point that could be used to develop a dual-wavelength method to account for the spectral interference from dissolved lignin in pulp bleaching streams, a critical procedure for the success of the present method. This method is simple, rapid, sensitive, accurate, and has the potential for on-line applications.