Room temperature ionic liquid doped DNA network immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide

A novel electrochemical H2O2 biosensor was constructed by embedding horseradish peroxide (HRP) in a 1-butyl-3-methylimidazolium tetrafluoroborate doped DNA network casting on a gold electrode. The HRP entrapped in the composite system displayed good electrocatalytic response to the reduction of H2O2. The composite system could provide both a biocompatible microenvironment for enzymes to keep their good bioactivity and an effective pathway of electron transfer between the redox center of enzymes, H2O2 and the electrode surface. Voltammetric and time-based amperometric techniques were applied to characterize the properties of the biosensor. The effects of pH and potential on the amperometric response to H2O2 were studied. The biosensor can achieve 95% of the steady-state current within 2 s response to H2O2. The detection limit of the biosensor was 3.5 mu M, and linear range was from 0.01 to 7.4 mM. Moreover, the biosensor exhibited good sensitivity and stability. The film can also be readily used as an immobilization matrix to entrap other enzymes to prepare other similar biosensors.

Synthesis and characterization of hyperbranched poly(ester-amide)s based on gallic acid and DL-2-aminobutyric acid

A novel AB(3)-type monomer was prepared from gallic acid and DL-2-aminobutyric acid, and used for the synthesis of the biocompatible hyperbranched poly(ester-amide)s by self-polycondensation. The polymers were characterized via FTIR and NMR spectroscopy and thermal analysis, and the average degree of branching of the polymers was estimated to be 0.75. The polymers with abundant acetyl end groups were found to be amorphous with lower intrinsic viscosity, better thermal stability and excellent solubility.

Study on crystalline morphology of poly(L-lactide)-poly(ethylene glycol) diblock copolymer

Crystallization behavior, structural development and morphology evolution in a series of diblock copolymers Of poly(L-lactide)-blockpoly(ethylene glycol) (PLLA-b-PEG) were investigated via differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy and atomic force microscopy. In these copolymers, both blocks are crystallizable and biocompatible. It was interesting that these PLLA-b-PEG diblock copolymers could form spherulites with banded textures, which was undercooling dependent. Single crystals with an abundance of screw dislocations were also observed via AFM. Such results indicated that these ringed spherulites and single crystals were formed during the crystallization of the PLLA blocks.

Poly-L-lysine functionalization of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) were covalently functionalized with biocompatible poly-L-lysine, which is useful in promoting cell adhesion. SWNTs played an important role as connectors to assemble these active amino groups of poly-L-lysine, which provided a relative "friendly" and "soft" environment for further derivation, such as attaching bioactive molecules. As an application example, by further linking peroxidase, an amplified biosensing toward H2O2 concerning this assembly was investigated.

Electrogenerated chemiluminescence biosensor based on Ru(bpy)(3)(2+) and dehydrogenase immobilized in sol-gel/chitosan/poly(sodium 4-styrene sulfonate) composite material

A new electrogenerated chemiluminescence biosensor was fabricated by immobilizing ECL reagent Ru(bPY)(3)(2+) and alcohol dehydrogenase in sol-gel/chitosan/poly(sodium 4-styrene sulfonate) (PSS) organically modified composite material. The component PSS was used to immobilize ECL reagent Ru(bpy)(3)(2+) by ion-exchange, while the addition of chitosan was to prevent the cracking of conventional sol-gel-derived glasses and provide biocompatible microenvironment for alcohol dehydrogenase. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate and it was much simpler than previous double-layer design. The detection limit was 9.3 x 10(-6) M for alcohol (S/N = 3) with a linear range from 2.79 x 10(-5) to 5.78 x 10(-2) M. With ECL detection, the biosensor exhibited wide linear range, high sensitivity and good stability.

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized in DNA films on a gold electrode

A novel third-generation hydrogen peroxide (H2O2) biosensor was developed by immobilizing horseradish peroxidase (HRP) on a biocompatible gold electrode modified with a well-ordered, self-assembled DNA film. Cysteamine was first self-assembled on a gold electrode to provide an interface for the assembly of DNA molecules. Then DNA was chemisorbed onto the self-assembled monolayers (SAMs) of cysteamine to form a network by controlling DNA concentration. The DNA-network film obtained provided a biocompatible microenvironment for enzyme molecules, greatly amplified the coverage of HRP molecules on the electrode surface, and most importantly could act as a charge carrier which facilitated the electron transfer between HRP and the electrode. Finally, HRP was adsorbed on the DNA-network film. The process of the biosensor construction was followed by atomic force microscopy (AFM). Voltammetric and time-based amperometric techniques were employed to characterize the properties of the biosensor derived. The enzyme electrode achieved 95% of the steady-state current within 2 s and had a 0.5 mu mol l(-1) detection limit of H2O2. Furthermore, the biosensor showed high sensitivity, good reproducibility, and excellent long-term stability.

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 powder

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder as negative electrode material of Ni-MH battery have been investigated at different temperatures. The calculated results show that the apparent activation enthalpy of the charge-transfer reaction is 43.89 kJ mol(-1), and the activation energy of hydrogen diffusion is 21.03 kJ mol(-1). The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. As a result, the maximum discharge capacity, activation property and high-rate dischargeability are greatly improved with increasing temperature. However, the charge retention and the cycling stability degrade with the increase of the temperature.

Electrochemical characteristics and microstructure of Zr0.9Ti0.1Ni1.1Mn0.6V0.3-LaNi5 composite hydrogen storage alloys

AB(2-x)%LaNi5 (x =0, 1, 5, 10) composite alloys were prepared by melting Zr0.9Ti0.1Ni1.1Mn0.6V0.3 with a small amount of LaNi5 alloy as addition. The microstructure and electrochemical characteristics of the composite alloys were investigated by means of XRD, SEM, EDS and electrochemical measurements. It was shown that LaNi5 addition does not change the basic hexagonal C14 Laves phase of AB(2) alloys, but some second phases have segregated. It was found that the addition of LaNi5 greatly improves the activation property, high-rate dischargeability (HRD) and charge-discharge cycling stability of AB(2) Laves phase alloy. At current density of 1200 mA/g, HRD of the alloy increases from 38.92% (x =0) to 60.09% (x = 10). The capacity retention of the alloy after 200 charge-discharge cycles increases from 57. 10% (x = 0) to 83.86% (x = 5) and 67.31% (x = 10). The improvement of the electrochemical characteristics caused by LaNi5 addition seems to be related to formation of the second phases.

Structures and electrochemical characteristics of several kinds of alloys

The structures and the electrochemical characteristics of La0.7-xCexMg0.3Ni2.8Co0.5 (x = 0.1-0.5) alloy, Ti0.25-xZrxV0.35Cr0.1Ni0.3 (x = 0.05-0.15) alloy and AB(3battery in which AB(3

Electrochemical characteristic of LaNi-based hydrogen storage alloys

Effect of purity of alloy components on the electrode performance of LaNi2 alloys was investigated. The results showed the purity of components had less effect on discharge capacity and self-discharge of LaNi2 alloys. Partial substitution of Al or Mn for Ni greatly improved discharge properties of LaNi2-xAlx, or LaNi2-yMny alloys as negative electrodes in MFl-Ni battery, 0.15less than or equal toxless than or equal to0.25; 0.15less than or equal toyless than or equal to0.25. In addition, surface treatment of LaNi1.8Al0.2 alloy electrode was performed by polymerizing cis-butenedioate with Co-60- gamma -ray radiation, which. had better affect on self-discharge and cycle life of the alloy electrodes at low temperature(-28 C-degrees).

Self-gelatinizable copolymer immobilized glucose biosensor based on Prussian Blue modified graphite electrode

A novel poly(vinyl alcohol) grafting 4-vinylpyridine self-gelatinizable copolymer was adapted to immobilize glucose oxidase. The reduction of hydrogen peroxide (H2O2) was detected at a Prussian Blue (PB) modified graphite electrode. A stable and sensitive glucose amperometric biosensor is described. The copolymer is a good biocompatible polymer in which the glucose oxidase retains high activity. Moreover, the copolymer can adhere firmly to the inorganic PB membrane. The sensor showed an apparent Michaelis-Menten constant of 18 +/- 0.2 mM and a maximum current density of 1.14 mu A cm(-2) mM(-1). The linear range is from 5 mu M to 4.5 mM glucose and the detection limit is 0.5. mu M glucose. The catalytic efficiency of PB for the reduction of H2O2 is higher than that for the oxidation of H2O2. Glucose concentrations in serum samples from healthy persons and diabetic patients were determined using the sensor. The results compared well with those provided by the hospital using a spectroscopy method.

Irreversible capacity loss of graphite electrode in lithium-ion batteries

The irreversible capacity loss of the carbon electrode in lithium-ion batteries at the first cycle is caused mostly by surface film growth. We inspected an unknown irreversible capacity loss (UICL) of the natural graphite electrodes. The charge/discharge behavior of graphite and meso-phase carbon microbeads heat-treated at 2800 degrees C (MCMB28) as the materials of the carbon anode in the lithium-ion battery were compared. It was found that the capacity loss of the natural graphite electrode in the first cycle is caused not only by surface film growth, but also by irreversible lithium-ion intercalation on the new formed surface at the potential range of lithium intercalation, while the capacity loss of the MCMB28 electrode is mainly originated from surface film growth. The reason for the difference of their irreversible capacity losses of these two kinds of carbon material was explained in relation to their structural characteristics. (C) 1997 Published by Elsevier Science S.A.

An electrochemical study of prussian blue microcrystallines mixed in PEO400 polymer electrolyte by solid-state voltammetry

The electrochemistry of Prussian blue mixed in a polymer medium containing MClO4 (M = Li+, Na+, K+, TBA(+)) as the supporting electrolyte was studied by means of solid-state voltammetry. This approach is new in Prussian blue studies. The behavior of PB in polymer electrolytes is somewhat similar to the well-known behavior for an electrochemically synthesized PB film in aqueous media. Besides, K+, Li+ and Na+ ions can also transport through the crystal of PB because of its zeolitic nature. The transport of TBA(+) ions is possible. Kinetic control lies in the diffusion of cations in and out of the lattice of Prussian blue. Reduction waves of Prussian blue depend on both the size and type of cations. PB is very stable upon electrochemical cycling in polymer electrolytes and air. This system may be used in rechargeable batteries and electrochromic devices.

GAMMA-RADIATION INDUCED CROSS-LINKED PEO-LICLO4 SOLID-ELECTROLYTE SYSTEM

Aimed at raising the room temperature ionic conductivity of PEO-based solid polymer electrolyte and considered that the ionic conduction preferentially occurs in the amorphous phase, we lightly crosslinked the high MW PEO through gamma-irradiation and further suppressed the residual crystallinity by plasticizing with propylene carbonate. By incorporating LiClO4 salt to the above described polymer host, the ambient (25 degrees C) ionic conductivity of the electrolyte system could reach as high as 6.8 X 10(-4) S/cm. As the electrolyte was a crosslinked system, it was mechanically self-supportable. Based on the preliminary results of the electrochemical performance of the secondary lithium battery, assembled by using this kind of solid electrolyte and polyaniline as positive electrode, it is realized that the electrolyte thus prepared is of high expectancy.