Electrochemical immunosensor using p-aminophenol redox cycling by hydrazine combined with a low background current

Signal amplification and noise reduction are crucial for obtaining low detection limits in biosensors. Here, we present an electrochemical immunosensor in which the signal amplification is achieved using p-aminophenol (AP) redox cycling by hydrazine, and the noise level is reduced by implementing a low background current. The redox cycling is obtained in a simple one-electrode, one-enzyme format. In a sandwich-type heterogeneous immunosensor for mouse IgG, an alkaline phosphatase label converts p-aminophenyl phosphate into AP for 10 min. This generated AP is electrooxidized at an indium tin oxide (ITO) electrode modified with a partially ferrocenyl-tethered dendrimer (Fc-D). The oxidized product, p-quinone imine (QI), is reduced back to AP by hydrazine, and then AP is electrooxidized again to QI, resulting in redox cycling. Moreover, hydrazine protects AP from oxidation by air, enabling long incubation times. The small amount of ferrocene in a 0.5% Fc-D-modified ITO electrode, where 0.5% represents the ratio of ferrocene groups to dendrimer amines, results in a low background current, and this electrode exhibits high electron-mediating activity for AP oxidation. Moreover, there is insignificant hydrazine electrooxidation on this electrode, which also results in a low background current. The detection limit of the immunosensor using a 0.5% Fc-D-modified electrode is 2 orders of magnitude lower than that of a 20% Fc-D-modified electrode (10 pg/mL vs 1 ng/mL). Furthermore, the presence of hydrazine reduces the detection limit by an additional 2 orders of magnitude (100 fg/mL vs 10 pg/mL). These results indicate that the occurrence of redox cycling combined with a low background current yields an electrochemical immunosensor with a very low detection limit (100 fg/mL). Mouse IgG could be detected at concentrations ranging from 100 fg/mL to 100 microg/mL (i.e., 9 orders of magnitude) in a single assay.     

The fabrication of vertically aligned and periodically distributed carbon nanotube bundles and periodically porous carbon nanotube films through a combination of laser interference ablation and metal-catalyzed chemical vapor deposition

Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 μm in width, and 50-200 μm in length, are grown atop the patterned catalyst over areas spanning 8 cm(2). The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.     

Wide-band flat-gain optical amplifier using Hafnia and zirconia erbium co-doped fibres in double-pass parallel configuration

ABSTRACT

A new compact and wide-band erbium-doped fibre amplifier (EDFA) was demonstrated by combining Hafnia-bismuth Erbium co-doped fibre (HB-EDF) and zirconia–yttria–aluminum Erbium co-doped fibre (Zr-EDF) as a hybrid gain medium, in parallel double-pass configuration. The proposed amplifier comprises a 0.5?m long HB-EDF and 4?m long Zr-EDF optimized for C- and L-band operations, respectively. The HB-EDF and Zr-EDF has erbium ion concentration of 12,500?ppm and 2800?ppm, respectively. At -10 dBm input signal, a wide-band flat gain of 15.7?dB is achieved with gain fluctuation of less than 1.5?dB within a wavelength region from 1525 to 1600?nm. Compared to same configuration of HB-EDF and Zr-EDF amplifiers which are using two pieces of HB-EDF and Zr-EDF, respectively with the same total amount of erbium ions, the proposed EDFA with hybrid gain medium provides even better performances in term of flat gain, bandwidth and noise figure.     

Uncertain supply chain network design considering carbon footprint and social factors using two-stage approach

Sustainable development has become one of the leading global issues over the period of time. Currently, implementation of sustainability in supply chain has been continuously in center of attention due to introducing stringent legislations regarding environmental pollution by various governments and increasing stakeholders’ concerns toward social injustice. Unfortunately, literature is still scarce on studies considering all three dimensions (economical, environmental and social) of sustainability for the supply chain. An effective supply chain network design (SCND) is very important to implement sustainability in supply chain. This study proposes an uncertain SCND model that minimizes the total supply chain-oriented cost and determines the opening of plants, warehouses and flow of materials across the supply chain network by considering various carbon emissions and social factors. In this study, a new AHP and fuzzy TOPSIS-based methodology is proposed to transform qualitative social factors into quantitative social index, which is subsequently used in chance-constrained SCND model with an aim at reducing negative social impact. Further, the carbon emission of supply chain is estimated by considering a composite emission that consists of raw material, production, transportation and handling emissions. In the model, a carbon emission cap is imposed on total supply chain to reduce the carbon footprint of supply chain. To solve the proposed model, a code is developed in AMPL software using a nonlinear solver SNOPT. The applicability of the proposed model is illustrated with a numerical example. The sensitivity analysis examines the effects of reducing carbon footprint cap, negative social impacts and varying probability on the total cost of the supply chain. It is observed that a stricter carbon cap over supply chain network leads to opening of more plants across the supply chain. In addition, carbon footprint of supply chain is found to be decreased in certain extent with the reduction in negative social impacts from suppliers. The carbon footprint of the supply chain is found to be reduced with increasing certainty of material supply from the suppliers. The total supply chain cost is observed to be augmented with increasing probability.     

Optical and electrical smart response of chemically stabilized graphene oxide

Graphene oxide (GO) was prepared using a modified Hammer’s technique and by utilizing a sonochemical approach. The paper deals with the synthesis and the characterization of GO besides the structural, morphological, optical and electrical properties of GO. Phase formation of the prepared sample was examined with powder X-ray diffraction (XRD), the typical surface morphology was carried out by utilizing Scanning electron microscopy (SEM) and the high resolution Transmission Electron Microscopy (HR-TEM). The different functional groups were recognized by utilizing FT-IR and Raman spectroscopy. The optical properties were studied utilizing optical absorption and photoluminescence (PL) spectra. At various frequencies and temperatures the dielectric properties of the GO, such as the dielectric constant, the dielectric loss, and AC conductivity were studied. Further, the electrical behaviour of GO was analysed using I-V and C-V characteristics. These novel findings shed focus on high yield electronic material GO, which can only be realized as the field moves forward and makes more significant advances in smart opto-electronic devices.     

Environmental and economic issues concerning the use of wet scrubbers coupled to bagasse-fired boilers: a case study in the Brazilian sugarcane industry

Clean Technologies and Environmental Policy - For decades, wet scrubbers have been used to control particulate matter (PM) emitted by bagasse-fired boilers in the sugarcane industry. This choice...     

Influence of surface scattering on the anomalous conductance plateaus in an asymmetrically biased InAs/In(0.52)Al(0.48)As quantum point contact

We study of the appearance and evolution of several anomalous (i.e., G < G(0) D 2e(2)/h) conductance plateaus in an In(0.52)Al(0.48)As/InAs quantum point contact (QPC). This work was performed at T = 4:2 K as a function of the offset bias ΔV(G) between the two in-plane gates of the QPC. The number and location of the anomalous conductance plateaus strongly depend on the polarity of the offset bias. The anomalous plateaus appear only over an intermediate range of offset bias of several volts. They are quite robust, being observed over a maximum range of nearly 1 V for the common sweep voltage applied to the two gates. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. This assertion is supported by non-equilibrium Green function simulations of the conductance of a single QPC in the presence of dangling bonds on its walls. Our simulations show that a spin conductance polarization as high as 98% can be achieved despite the presence of dangling bonds. The maximum in is not necessarily reached where the conductance of the channel is equal to 0:5G(0).     

Influence of temperature, voltage and hydrogen on the reversible transition of electrical conductivity in sol–gel grown nanocrystalline TiO2 thin film

Undoped nanocrystalline p-type TiO₂ thin film was deposited by sol–gel method on a thermally oxidized p-Si (2–5 Ω cm resistivity and $ \left\langle {100} \right\rangle $ orientation) substrate. The thin film was characterized by two-dimensional X-ray Diffraction (2D-XRD) and Field Emission Scanning Electron Microscopy (FESEM) to confirm the formation of stable nano crystalline anatase titania and to determine the grain size (~10 nm). Optical absorption spectroscopy was carried out to ascertain the band gap of the material. Two lateral Pd contacts were used as the metal electrodes to TiO₂ thin film to study the electrical conductivity. A clear p- to n-type transition was observed at 240 °C and a bias voltage of 0.83 V and the effect was enhanced on exposure to H₂ gas. The thin film showed fully n-type conductivity at 275 °C and 0.1 V. However, the reversal of the type of conductivity from n- to p-type was observed below 240 °C during lowering the temperature. The creation of oxygen vacancy and the diffusion of lattice oxygen to the surface of TiO₂ thin film might be the most possible mechanism of such transitions. Presence of hydrogen enhanced the process.     

Synthesis and characterization of TiC-reinforced iron-based composites Part II on mechanical characterization

The hardness, impact toughness and wear resistance properties of Fe-TiC composites, synthesized by aluminothermic reduction of an industrial waste, have been evaluated. The wear resistance property of the composites has been compared with some standard wear resistant materials. It has been found that the wear resistance property of the Fe-TiC composites with mostly pearlitic, fully pearlitic and pearlitic plus cementite type matrix with about 7 to 8 vol% TiC is better than that of a standard high chromium iron. The wear resistance property of ferritic and mostly ferritic type matrix with about 5 vol% TiC is better than that of a standard bearing steel.