Dispersion of single-walled carbon nanotubes in poly(diallyldimethylammonium chloride) for preparation of a glucose biosensor

Poly(diallyldimethylammonium chloride) (PDDA) was chosen to disperse single-walled carbon nanotubes (SWCNTs). The optimal conditions to prepare stable PDDA–SWCNTs aqueous dispersions were presented. Then, the positively charged PDDA–SWCNTs composite and negatively charged glucose oxidase (GOD) were employed to fabricate multilayer films on platinum (Pt) electrodes by layer-by-layer self-assembly technique. The consecutive growth of the multilayer films was confirmed by quartz crystal microbalance. Electrochemical measurements were used to study the properties of the proposed biosensor. Results demonstrated that SWCNTs were evenly dispersed within the PDDA films and efficiently improved the conductivity of the resulting films. Among the biosensors, the one based on seven layers of multilayer films got the best performance. It showed wide linear range of 0.05–12 mM, high sensitivity of 63.84 μA/(mM cm²), low detection limit of about 4 μM and small value of the apparent Michaelis–Menten constant, 8.46 mM. In addition, the biosensor also exhibited good suppression of interference and long-term operational stability. This protocol could be used to immobilize other enzymes to construct a range of biosensors.     

Preparation of Ag–Au nanoparticle and its application to glucose biosensor

In this paper, Ag–Au nanoparticles are produced in sodium-bis(2-ethylhexyl)-sulfosuccinate (AOT)–cyclohexane reverse micelle system. The properties of the obtained nanoparticles are characterized with transmission electron microscope (TEM) and UV–vis absorption spectrophotometer. Glucose biosensors have been formed with glucose oxidase (GOx) immobilized in Ag–Au sol. GOx are simply mixed with Ag–Au nanoparticles and crosslinked with a polyvinyl butyral (PVB) medium by glutaraldehyde. Then a platinum electrode is coated with the mixture. The effects of the various molar ratios of Ag–Au particles with respect to the current response and the stability of the GOx electrodes are studied. The experimental results indicate the current response of the enzyme electrode containing Ag–Au sol increase from 0.32 to 19 μA cm⁻² in the solution of 10 mM β-d-glucose. In our study, the stability of enzyme electrodes is also enhanced.     

Synthesis and luminescence of red MEH-PPV:P3OT polymer

This paper investigates the synthesis processes for poly(3-octylthiophene) (P3OT) and poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). The proton nuclear magnetic resonance (¹H NMR) and the Fourier transform infrared spectrophotometer (FTIR) were used to identify the chemical structure and functional group of synthesized polymers, respectively. The efficient Förster energy transfer from P3OT to MEH-PPV and the dilution of MEH-PPV with P3OT leaded to an enhanced red emission. When the concentration of P3OT was 30 wt%, the optimal photoluminescence (PL) intensity of MEH-PPV:P3OT was obtained, with wavelength at 580 nm. A PL quenching phenomenon was observed owing to the higher blending concentration of P3OT. The current density was 0.204 A/cm² at 1.3 V for the red polymer light-emitting diode with the structure of Al/MEH-PPV:P3OT/ITO, and the CIE chromaticity coordinates were at x = 0.66 and y = 0.34.     

Multiwalled carbon nanotubes grafted chitosan nanobiocomposite: A prosperous functional nanomaterials for glucose biosensor application

Multiwalled carbon nanotubes (MWNTs) grafted chitosan (CS) nanowire (NW) was prepared by phase separation method. Glucose oxidase (GOx) was sequentially immobilized into MWNT-CS-NW to obtain MWNT-CS-NW/GOx biosensor. Field emission scanning electron microscopy (FESEM) images of MWNT-CS-NW/GOx reveals the existence of MWNT and CS. Cyclic voltammetry and amperometry were used to evaluate the electrochemical determination of glucose. The MWNT-CS-NW/GOx biosensor shows an excellent performance for glucose at +0.34 V with a high sensitivity (5.03 μA/mM) and lower response time (3 s) in a wide concentration range of 1-10 mM (correlation coefficient of 0.9988). In addition, MWNT-CS-NW/GOx biosensor possesses better reproducibility, storage stability and there is negligible interference from other electroactive components.     

Fabrication of polypyrrole–glucose oxidase biosensor based on multilayered interdigitated ultramicroelectrode array with containing trenches

A miniature glucose biosensor has been developed based on electropolymerization of polypyrrole–glucose oxidase on a multilayered gold interdigitated ultramicroelectrode array with containing trenches. The basal band ultramicroelectrode with a functional width of 362 nm is fabricated using multilayered materials and conventional photolithographic techniques. The electrode surface is inside the containing trenches, the depth of which is larger than 1.5 μm. High quality electrodes with uniform geometries are characterized by microscopy and electrochemical techniques. The corrosion resistance is investigated on exposure to the normal saline, which indicates that the electrodes are adequate for acute experiments lasting a few hours. Fabricated by electropolymerization, the glucose oxidase/polypyrrole (GOx/PPy) biosensors can be used for detecting glucose concentration in the linear range of 0–10 mmol/L, with a sensitivity of 13.4 nA/(mmol L) and a correlation coefficient of 0.998, respectively.     

Electrogenerated chemiluminescence sensor for itopride with Ru(bpy)3-doped silica nanoparticles/chitosan composite films modified electrode

A electrogenerated chemiluminescence (ECL) sensor for itopride was developed based on tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-doped silica (RuDS) nanoparticles/biopolymer chitosan composites membrane modified glassy carbon electrode (GCE). The RuDS nanoparticles (52 ± 5 nm) were prepared by a modified Stőber synthesis method and were characterized by electrochemical, fluorometric and transmission electron microscopy technology. The Ru(bpy)₃²⁺ encapsulation interior of the silica nanoparticle maintains its electrochemical activities and also reduces Ru(bpy)₃²⁺ leaching from the silica matrix when immersed in water due to the electrostatic interaction. The ECL analytical performances of this ECL sensor for itopride based on its enhancement ECL emission of Ru(bpy)₃²⁺ were investigated in details. Under the optimum condition, the enhanced ECL intensity was linear with the itopride concentration in the range of 1 × 10⁻⁸ to 2 × 10⁻⁵ g/mL (R = 0.9978). The detection limit was 3 × 10⁻⁹ g/mL, and the relative standard deviation was 2.3% for 8 × 10⁻⁸ g/mL itopride (n = 11). The method was successfully applied to the determination of itopride in pharmaceutical and human serum samples with satisfactory results. The as-prepared ECL sensor for the determination of itopride displayed good sensitivity and stability.     

Development of a bienzyme system based on sugar–lectin biospecific interactions for amperometric determination of phenols and aromatic amines

Bienzyme electrode with horseradish peroxidase (HRP) and glucose oxidase (GOD) multilayers was constructed based on sugar–lectin biospecific interactions for amperometric determination of phenolic compounds and aromatic amines. Atomic force microscopy (AFM) was applied to monitor the uniform layer-by-layer assembly of concanavalin A (Con A) and HRP or GOD on polyelectrolyte precursor film-modified Au electrode. Substituted phenolic compounds and aromatic amines could be determined with in situ generation of H₂O₂ by GOD-catalyzed oxidation of glucose. The parameters of the biosensor including the number of assembled HRP and GOD layer, and the concentrations of glucose were optimized. The linear range for the determination of catechol and p-phenyldiamine was 6.0–60.0 μmol L⁻¹ and 7.6–68.4 μmol L⁻¹ with detection limit of 0.9 μmol L⁻¹ and 0.4 μmol L⁻¹, respectively. The biosensor possessed high sensitivity and fast response for phenolic compounds and 95% of the maximum response could be reached in about 3 s. Glucose, ascorbic acid, tartaric acid, citric acid and starch exhibited no interference for the detection. The biosensor presented high stability due to the design for in situ generation of H₂O₂ with bienzyme system.     

Evaluation of amperometric glucose biosensors based on glucose oxidase encapsulated within enzymatically synthesized polyaniline and polypyrrole

In this article potential and suitability of enzymatically synthesized conducting polymers polyaniline (PANI) and polypyrrole (PPY) for fabrication of enzymatic amperometric glucose biosensors were evaluated. The polymerisation of these polymers was induced by catalytic activity of glucose oxidase (GOx) from Penicillium vitale cross-linked by glutaraldehyde (GA) on the graphite rod electrode (GOx-electrode) surface. The main precursors for initiation of polymerisation reactions were hydrogen peroxide as an initiator of polymerisation reaction and β-d-gluconic acid as a medium, which reduced the pH towards acidic one is the most suitable for the formation of PANI and PPY. During the polymerisation reactions the immobilized GOx was self-encapsulated within formed PANI or PPY layers in order to form GOx/PANI- and GOx/PPY-modified electrodes (GOx/PANI-electrode and GOx/PPY-electrode, respectively). Kinetic properties of GOx, which is acting as a biocatalyst in GOx/PANI- and GOx/PPY-electrodes, were studied and results were compared with GOx-electrode. The results show that in both GOx/PANI- and GOx/PPY-electrodes self-encapsulated GOx exhibited different parameters of catalysed reaction kinetics due to increasing diffusion limitations if compared with that of the GOx-electrode and it allowed the detection of glucose in a wider concentration interval. Moreover, both GOx/PANI- and GOx/PPY-electrodes exhibited good operational stability and reproducibility of analytical signal. The electrochemical characteristics of formed PANI and PPY in the GOx/PANI- and GOx/PPY-electrodes were also determined. In addition, the influence of temperature, pH and common interfering compounds on the steady-state current response of modified electrodes were investigated and discussed.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized in zirconium phosphate nanosheets film

Myoglobin (Mb) is incorporated on a novel matrix—zirconium phosphate nanosheets (ZrPNS) and immobilized at a glassy carbon electrode surface. UV–vis spectra and electrochemical measurements show that the matrix is well biocompatible and can retain the bioactivity of immobilized Mb. The direct electron transfer between Mb and electrode exhibits a couple of well-defined redox peaks. The cathodic and anodic peaks are located at −0.340 and −0.280 V vs. Ag/AgCl, respectively. The ZrPNS can improve the electron transfer between Mb and electrode with an electron transfer constant of 5.6 s⁻¹. Meanwhile, the catalytic ability of the protein toward the reduction of H₂O₂, O₂, NaNO₂, trichloroacetic acid (TCA) is also studied and a third-generation biosensor is subsequently fabricated. The linear range of biosensor to H₂O₂ is from 8 × 10⁻⁷ to 1.28 × 10⁻⁵ M with the limit detection of 1.4 × 10⁻⁷ M. The small apparent Michaelis–Menten constant (34 μM) suggests that Mb/ZrPNS film performs good affinity with H₂O₂. The biosensor also exhibits acceptable stability and reproducibility. This work paves a way to develop other biologic active materials in this kind of nanosheets for constructing novel biosensors.     

How age affects the speed of perception of computer icons

The use of computers is constantly increasing. At the same time the population of the industrialised world is aging. In this study we investigated the speed with which users of different ages can find a specific computer icon from a group of others. Our results show that search performance slows with age when calculated across all three levels of inter-icon spacing (χ² (4) = 14.904, p < .05) and icon size (χ² (4) = 15.674, p < .05) used in this study. However, individual variability in search performance was very high within all age groups. Our study suggests that icons used in graphical user interfaces should be at least about 1 degree in size (about 0.7 cm at a viewing distance of 40 cm) for the majority of users to be able to perform their computerised tasks with relative ease. Also, the inter-icon spacing should be moderate, preferably about the same as the icon size. Ideally user interfaces should be adaptable to individual user needs and preferences.     

A miniaturized glucose biosensor based on the coimmobilization of glucose oxidase and ferrocene perchlorate in nafion at a microdisk platinum electrode

A miniaturized glucose biosensor based on the coimmobilization of Fc⁺ (ferrocene perchlorate)/GOD (glucose oxidase) in nafion film at the surface of a microdisk platinum electrode was fabricated and successfully used for the amperometric determination of glucose. The influences of various experimental conditions, including the relative amounts of glucose oxidase in diluted nafion aqueous solution, the concentration of ferrocene perchlorate and oxygen etc., were investigated in this paper. Ferrocene perchlorate as a redox mediator could catalyze the oxidation of the generated H₂O₂ based on the enzymatic reaction of glucose in the presence of glucose oxidase and oxygen at a favorable lower working potential (ca. 0.25 V vs. SCE). Moreover, it could also oxidize the reduced flavin adenine dinucleotide (FADH₂) of glucose oxidase directly in anaerobic environment. The response time and the detection limit under an optimal parameters were 2 min and 1 × 10⁻⁵ M, respectively. The interferences of ascorbic acid and uric acid could be obviously reduced because of the ion-selective characteristics of nation film and a favorable lower working potential. From the Michealis-Menten analysis, the apparent Michaelis constants for glucose and the maximum limiting currents determined were 10.7 mM and 5.1 nA for the incorporation of Fc⁺ in 1.00 mM Fc⁺ solution, 7.06 mM and 5.85 nA in 2.00 mM Fc⁺, respectively. Moreover, using water instead of organic solvents for nafion dilution made this enzyme electrode exhibit a good stability and reproducibility for a long-term use.     

EPR and DRS evidence for NO2 sensing in Al-doped ZnO

Zinc oxide (ZnO) is a well-known semiconducting multifunctional material wherein properties right from the morphology to gas sensitivity can be tailor-made by doping or surface modification. Aluminum (Al)-incorporated porous zinc oxide (Al:ZnO) exhibits good response towards NO₂ at low-operating temperature. The NO₂ gas concentration as low as 20 ppm exhibits S = 17% for 5 wt.% Al-incorporated ZnO. The NO₂ response increases with operating temperature and concentration and reaches to its maximum at 300 °C without any interference from other gases such as SO₃, HCl, LPG and alcohol. Physico-chemical characterization likes differential thermogravimetric analysis (TG-DTA) electron paramagnetic resonance (EPR) and diffused reflectance spectroscopy (DRS) have been used to understand the sensing behavior for pure and Al-incorporated ZnO. The TG-DTA depicts formation of ZnO phase at 287 °C. The EPR study reveals distinct variation for O⁻ (g = 2.003) and Zn interstitial (g = 1.98) defect sites in pure and Al:ZnO. The DRS studies elucidate signature of adsorbed NO_x species in aluminium-incorporated zinc oxide indicating its tendency to adsorb these species even at low temperatures. This paper is an attempt to correlate the gas sensing behavior with the physico-chemical studies such as EPR and DRS.     

层层累积技术制备基于纳米碳管的葡萄糖生物传感器

以多壁纳米碳管(MWCNTs)为电子媒介体和酶的吸附载体,利用层层累积的自组装技术固定葡萄糖氧化酶(GOx)的多层(MWCNTs/GOx)n复合薄膜修饰电极,制备了一种新型葡萄糖生物传感器。结果表明:传感器对葡萄糖的响应电流值随着MWCNTs/GOx复合薄膜层数的不同而变化,当MWCNTs/GOx复合薄膜的层数为6时,响应电流值达到最大。(MWCNTs/GOx)6复合薄膜修饰的葡萄糖生物传感器对3×10-2mol/L葡萄糖的响应电流为1.63μA,响应时间仅为6.7 s。该生物传感器检测的线性范围为5×10-4~1.5×10-2mol/L,最低检测浓度可达0.9×10-4mol/L。     

White organic light-emitting devices with non-doped-type structure

A non-doped-type structure was proposed for obtaining organic light-emitting devices with high-efficiency and full-spectrum white light emission. The device structure included indium tin oxide glass substrate/450 Å 4,4′,4″-tris{N-(3-methylphenyl)-N-phenylamin}triphenylamine (m-MTDATA) hole injection layer/100 Å N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biph-enyl-4,4′-diamine (NPB) hole transport layer/150 Å 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) blue emitting layer/ultrathin [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H, 5H-benzo[ij] quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2) yellow-emitting layer/ 80 Å 4,7-diphenyl-1,10-phenanthroline (BPhen) electron transporting layer and hole blocking layer/600 Å tris (8-hydroxyquinoline) aluminium (Alq3) electron-transporting layer /10 Å lithium fluoride (LiF)/aluminum (Al). A white emission (Commission Internationale de l’Eclairage 1931 chromaticity coordinate) (X = 0.3556, Y = 0.3117) at 5 V and (X = 0.282, Y = 0.2658) at 15 V was obtained. Its luminance was 11,497 cd/m² at 15 V, and the maximum efficiency was 4.8 lm/W at 5 V.     

Highly efficient and stable white organic light emitting diode with triply doped structure

A triply doped white organic light emitting diode with red and blue dyes in the light emitting layer and a green dye in another layer is proposed. The device structure was CuPc(12 nm)/NPB(40 nm)/ADN:DCJTB(0.2%):TBPe(1%)(50 nm)/Alq:C545(0.5%)(12 nm)/LiF(4 nm)/Al. Here copper phthalocyanine (CuPc) is a buffer layer, N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) is a hole transporting layer, 9,10-di-(2-naphthyl) anthracene (ADN) is blue emitting layer, tris (8-quinolinolato)aluminium complex (Alq) is an electron transporting layer, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidy1-9-enyl)-4H- pyran (DCJTB), 2,5,8,11-tetra-butylperylene (TBPe), Coumarin6 and deveriative (C545) are red, blue and green dyes, respectively. This device shows a luminance of 21200 cd/m² at driving current of 400 mA/cm² and 1026 cd/m² at 20 mA/cm². Its efficiency is 6 cd/A and 3.11 Lm/W. It also shows a higher operating stability: the half lifetime is 22,245 h at an initial luminance of 100 cd/m², while the driving voltage increased only 0.3 V.     

Layer-by-layer construction of an active multilayer enzyme electrode applicable for direct amperometric determination of cholesterol

A biosensor for direct amperometric determination of cholesterol was constructed by a layer-by-layer nanothin film formation using cholesterol oxidase (COx) and poly(styrenesulfonate) on a monolayer of microperoxidase covalently-immobilized on Au–alkanethiolate electrodes. Cyclic voltammograms (CVs) of microperoxidase covalently-immobilized on mercaptopropionic acid- and aminoethanethiol-monolayer electrodes showed a redox wave with the formal potential of 0.40 V (versus Ag | AgCl | NaCl (sat.)). The formal potential and the apparent heterogeneous electron-transfer rate of immobilized microperoxidase were not specific with the inner Au–alkanethiolate layer. The biosensor shows a linear current response for cholesterol at the applied potential of 0 V in the concentration range of 0.2–3.0 mM with a correlation coefficient of 0.969. The current response of the biosensor for cholesterol was very rapid (response time <20 s) and was highly reproducible; sample standard deviation of the current response at the concentration of 1.5 mM in five individual determinations was 0.09. The magnitude of the amperometric response for cholesterol was 0.13 μA cm⁻² at the concentration of 1.5 mM. The inertness and stability of the biosensor towards the potential electrical interferents, -ascorbic acid, pyruvic acid and uric acid, was tested, and it was found that the biosensor rapidly responses to the addition of cholesterol even in the presence of these interferents.     

Highly efficient styrylamine-doped blue and white organic electroluminescent devices

We have developed highly efficient blue and white organic electroluminescent devices based on a blue fluorescent styrylamine dopant EBDP. The blue and white organic light emitting diodes (OLEDs) with the structures: Indium–tin oxide (ITO)/copper phthalocyanine(CuPc)/N,N′-bis-(1-naphenyl)-N,N′-biphenyl-1,1′-bipheny1-4-4′-diamine (NPB)/2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN):EBDP/tris(8-hydroxyquinoline)aluminum(Alq₃)/LiF/Al and ITO/CuPc/NPB/TBADN:EBDP: 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/Alq₃/LiF/Al were studied by using EBDP as blue dopant. For the blue device, the maximum luminance and maximum efficiency were 26961 cd/m² and 8.29 cd/A, respectively, the luminance at a current density 20 mA/cm² was 1597 cd/m². For the white device, the maximum luminance of 32,291 cd/m², maximum efficiency 8.31 cd/A and the luminance of 1413 cd/m² at a current density 20 mA/cm² were obtained. The slow decrease of efficiency with the increase of current density indicates weak exciton–exciton annihilation, which is resulted from the large steric hindrance due to the non-planar structure of the fluorescence dye EBDP.     

Periodic solutions of a class of nonlinear difference equations via critical point method

In this paper, we obtain some new sufficient conditions for the existence of nontrivial m-periodic solutions of the following nonlinear difference equation

by using the critical point method, where f: Z × R → R is continuous in the second variable, m ≥ 2 is a given positive integer, p_n+m = p_n for any n  Z and f(t + m, z) = f(t, z) for any (t, z)  Z × R, (−1)^δ = −1 and δ > 0.     

Inhibitive determination of metal ions by an amperometric glucose oxidase biosensor: Study of the effect of hydrogen peroxide decomposition

An amperometric glucose biosensor based on glucose oxidase immobilized in electrosynthesized poly-o-phenylenediamine was successfully applied to the determination of a wide group of heavy metals of environmental interest. The inhibition effects of Hg²⁺, Ag⁺, Cu²⁺, Cd²⁺, Pb²⁺, Cr³⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺ and also CrO₄²⁻ on glucose oxidase were studied. Collected data showed a reversible inhibition mechanism. Results about the quantitative analysis of metal ions in terms of detection limit, linear range, sensitivity and R.S.D. are discussed for each tested metal ion. The biosensor was able to discriminate two different oxidation states of chromium being able to reject Cr³⁺ and to detect the toxic species CrO₄²⁻. Also biosensor storage stability and response reproducibility were investigated.

Moreover, this study represents the first attempt of evaluating the effect of the hydrogen peroxide decomposition by metal ions on the response of an enzymatic biosensor based on the amperometric detection of the hydrogen peroxide. Experiments were performed with the aim to quantitatively evaluate, for any single metal ion, if this process is competitive with the inhibition of enzymatic reaction in the adopted experimental conditions.     

Fabrication and characterization of low temperature sintering PMN–PZN–PZT step-down multilayer piezoelectric transformer

For the fabrication as step-down multilayer piezoelectric transformer, piezoelectric properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (PMN–PZN–PZT) ceramics were optimized by ZnO–Li₂CO₃ (ZL) and Pb₃O₄ content. Effects of the additions on the structure, bulk density and electrical properties of ceramics were investigated. The results revealed that the proper additions of ZL with Pb₃O₄ content could modify the electrical properties of the PMN–PZN–PZT ceramics. The composition sintered at 995 °C with 0. 01 wt.% ZL and 0.10 wt.% Pb₃O₄ content showed higher values, which were listed as follows: d₃₃ = 256 pC/N, K_p = 0.60, Q_m = 1910, _r = 1032, tan δ = 0.0070 and r = 2.09 Ω. In addition, the step-down piezoelectric transformers with optimized PMN–PZN–PZT composites were fabricated and the characteristics as the output power and resistance loads were measured. Meanwhile, the step-down piezoelectric transformers sintered at 995 °C showed the favorable characteristics with a higher gain G of 0.204 and a lower temperature rise of 6 °C when the output power was 5 W, and the driving frequency were approximately constant (≈126 kHz) when the output power was from 5 to 13 W. Moreover, the maximum efficiency (90.2%) was obtained at load resistance of 10 Ω.