Highly sensitive photoelectrochemical immunoassay with enhanced amplification using horseradish peroxidase induced biocatalytic precipitation on a CdS quantum dots multilayer electrode

Herein we demonstrate the protocol of a biocatalytic precipitation (BCP)-based sandwich photoelectrochemical (PEC) horseradish peroxidase (HRP)-linked immunoassay on the basis of their synergy effect for the ultrasensitive detection of mouse IgG (antigen, Ag) as a model protein. The hybrid film consisting of oppositely charged polyelectrolytes and CdS quantum dots (QDs) is developed by the classic layer by layer (LbL) method and then employed as the photoactive antibody (Ab) immobilization matrix for the subsequent sandwich-type Ab-Ag affinity interactions. Improved sensitivity is achieved through using the bioconjugates of HRP-secondary antibodies (Ab(2)). In addition to the much enhanced steric hindrance compared with the original one, the presence of HRP would further stimulate the BCP onto the electrode surface for signal amplification, concomitant to a competitive nonproductive absorption that lowers the photocurrent intensity. As a result of the multisignal amplification in this HRP catalyzed BCP-based PEC immunoassay, it possesses excellent analytical performance. The antigen could be detected from 0.5 pg/mL to 5.0 ng/mL with a detection limit of 0.5 pg/mL.     

Amplified electrochemical detection of a cancer biomarker by enhanced precipitation using horseradish peroxidase attached on carbon nanotubes

An electrochemical nanoimmunosensor based on multiwall carbon nanotubes (MWCNTs)/gold nanoparticles (AuNPs) was developed for the amplified detection of prostate specific antigen (PSA). The amplified detection was achieved by the enhanced precipitation of 4-chloro-1-naphthol (CN) using a higher number of horseradish peroxidase (HRP) molecules attached on MWCNTs. The PSA nanoimmunosensor was fabricated by immobilizing a monoclonal anti-PSA antibody (anti-PSA) on the AuNP-attached thiolated MWCNT on a gold electrode. The sensor surface was characterized using scanning electron microscope, transmission electron microscope, quartz crystal microbalance, and electrochemical techniques. Cyclic and square wave voltammetric techniques were used to monitor the enhanced precipitation of CN that accumulated on the electrode surface and subsequent decrement in the electrode surface area by monitoring the reduction process of the Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox couple. Under the optimized experimental condition, the linear range and the detection limit of PSA immunosensor were determined to be 1.0 pg/mL to 10.0 ng/mL and 0.40 ± 0.03 pg/mL, respectively. The validity of the proposed method was compared with an enzyme-linked immunosorbent assay method in various PSA spiked human serum samples.     

Precipitation of an insoluble product on enzyme monolayer electrodes for biosensor applications: characterization by Faradaic impedance spectroscopy, cyclic voltammetry, and microgravimetric quartz crystal microbalance analyses.

Precipitation of an insoluble, insulating product on monolayer-functionalized electrodes enables the development of new electrochemical biosensors. Faradaic impedance spectroscopy and cyclic voltammetry are used to probe the electron-transfer resistance at the conductive support upon the accumulation of the insoluble product on the electrode surface. Similarly, microgravimetric quartz crystal microbalance, QCM, analyses were used to assay the formation of the precipitate on the electrode. A horseradish peroxidase, HRP, monolayer electrode is used to analyze H2O2 via the biocatalyzed oxidation of 4-chloro-1-naphthol (1) and the precipitation of the insoluble product (2). A bienzyme-layered electrode consisting of HRP and glucose oxidase, GOx, is used to sense glucose. Biocatalyzed oxidation of glucose by O2, in the presence of GOx, yields H2O2, and the generated hydrogen peroxide effects the formation of the insoluble product (2) in the presence of HRP. The insoluble product accumulated on the electrode, and the extent of the resulting electron-transfer resistance, correlated with the amounts of H2O2 or glucose, and appropriate calibration curves are extracted.     

Synthesis of nickel oxides nanoparticles on glassy carbon as an electron transfer facilitator for horseradish peroxidase: Direct electron transfer and H2O2 determination

In this study, horseradish peroxidase/nickel oxides nanoparticles/glassy carbon (HRP/NiO NPs/GC) electrode was prepared by first applying nickel oxides nanoparticles on glassy carbon surface and then horseradish peroxidase immobilized on the NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used as a diagnostic tools to identify the synthesized NiO NPs. Immobilized HRP showed an electrochemical redox behavior pertained to HRP(Fe(III)–Fe(II)) by direct electron transfer between protein and nanoparticles with a formal potential (E^0′) of ? 55.5 mV (vs. Ag/AgCl and 141.5 mV vs. NHE) in 50 mM phosphate buffer solution (PBS). The anodic charge transfer coefficient (α) and heterogeneous electron transfer rate constant (k_s) were 0.42 and 0.75 s^? 1, respectively. Biocatalytic activity of HRP/NiO NPs/GC electrode for reduction of hydrogen peroxide and application to hydrogen peroxide determination was exemplified.     

Improving the detection limit of anion-selective electrodes: an iodide-selective membrane with a nanomolar detection limit

The lower detection limit and the selectivity behavior of anion-selective electrodes (ISEs) are improved by using optimized inner solutions and membrane compositions. With a membrane based on the recently described ionophore [9]mercuracarborand-3, a detection limit of 2 x 10(-9) M has been achieved for iodide. Nevertheless, the improvements are less pronounced than in the case of cation ISEs. This is mainly due to the fact that so far no anion ISE is known with the extremely high selectivities of cation ISEs. If the membrane does not contain an ionophore, leaching of the ion exchanger from the membrane into the sample is also a relevant limiting factor except for ion exchangers of very high lipophilicity.     

Comparison of an enhanced versus a written feedback model on the management of Medicare inpatients with venous thrombosis

BACKGROUND: A multistate randomized study conducted under the Health Care Financing Administration's (HCFA's) Health Care Quality Improvement Program (HCQIP) offered the opportunity to compare the effect of a written feedback intervention (WFI) with that of an enhanced feedback intervention (EFI) on improving the anticoagulant management of Medicare beneficiaries who present to the hospital with venous thromboembolic disease. METHODS: Twenty-nine hospitals in five states were randomly assigned to receive written hospital-specific feedback (WFI) of feedback enhanced by the participation of a trained physician, quality improvement tools, and an Anticoagulant Management of Venous Thrombosis (AMVT) project liaison (EFI). Differences in the performance of five quality indicators between baseline and remeasurement were assessed. Quality managers were interviewed to determine perceptions of project implementation. RESULTS: No significant differences in the change from baseline to remeasurement were found between the two intervention groups. Significant improvement in one indicator and significant decline in two indicators were found for one or both groups. Yet 59% of all quality managers perceived the AMVT project as being successful to very successful, and more EFI quality managers perceived success than did WFI managers (71% versus 40%). In the majority of EFI hospitals, physician liaisons played an important role in project implementation. CONCLUSION: Study results indicated that the addition of a physician liaison, quality improvement tools, and a project liaison did not provide incremental value to hospital-specific feedback for improving quality of care. Future studies with larger sample sizes, lengthier follow-up periods, and interventions that include more of the elements shown to affect practice behavior change are needed to identify an optimal feedback model for use by external quality management organizations.     

Application of the method of splitting by physical processes for the computation of a hypersonic flow over an aircraft model of complex configuration

The capabilities of the computing complex developed at the Institute for Problems in Mechanics of the Russian Academy of Sciences are studied by the example of an external hypersonic flow over a model of an unmanned experimental aircraft X-43 of complex configuration. The program complex includes a generator of the unstructured surface and volumetric computational meshes and a series of computer codes that implement the integration of the closed system of Euler and Navier-Stokes equations using the method of splitting by physical processes on an unstructured mesh. The results of application of the developed numerical method on the generated unstructured computational meshes for three-dimensional modeling of the aerothermodynamics of the complex hypersonic aircraft X-43 are presented. The flow field and heat transfer processes in the entire region of the flow from the bow wave to the far wake are investigated. The configuration of the shock waves generated in the flow over a hypersonic flying vehicle (HFV) is studied. The effect of the angle of attack and free stream on the flow flown and the aerodynamic and thermal characteristics of the HFV surface is studied. The integral aerodynamic characteristics of X-43, lift coefficients C _L , and drag coefficients C _D are calculated for each regime of the flow. The HFV lift-drag ratio K dependences on the Mach number and angle of attack are found. The data of the X-43 flight and wind-tunnel tests are compared with the results of numerical modeling.     

Limitation of a giant amplification surge by photoinduced space charge accompanying an increase in the concentration of recombination centers in intrinsic threshold photoresistors with extracting contacts

An analysis is made of the dependence of Ĝ on V under conditions of a giant surge of the photoelectric gain Ĝ as the concentration of recombination impurities N increases, where V is the applied voltage and Ĝ is the value of G at the maximum point of the function G(N). It is shown that as a result of the space charge induced by the optical radiation the function Ĝ(V) exhibits strongly nonmonotonic behavior. The optimum voltage V _opt applied to the sample is determined for which Ĝ(V) reaches the maximum Ĝ _max. This nonmonotonic dependence of Ĝ on V does not correlate with heating of carriers or the lattice or by injection of charge from the contacts. Pis’ma Zh. Tekh. Fiz. 25, 1–8 (March 12, 1999)     

Effect of chaotic mixing on enhanced biological growth and implications for wastewater treatment: a test case with Saccharomyces cerevisiae

Mixing patterns and modes have a great influence on the efficiency of biological treatment systems. A series of laboratory experiments was conducted with a controlled, small-scale analog of a pilot wastewater aeration tank, consisting of two eccentrically placed cylinders. By controlling the rotation direction and speed of the two cylinders, it has been possible to develop chaotic flow fields in the space between the walls of the cylinders. Our experiments utilized Saccharomyces cerevisiae as the biological oxidation organism and air bubbles as the mixing agent supplied by a large fine pore diffuser to the cells in their exponential growth phase. The effect of various mixing patterns on cell growth was studied at different cylinder eccentricities, rotation directions and speeds. It was found that chaotic advection flow patterns: (a) enhanced growth, and (b) sped up the onset of maximal growth of the organism by 15-18% and 14-20%, respectively.     

Matrix generation within a macroporous non-degradable implant for osteochondral defects is not enhanced with partial enzymatic digestion of the surrounding tissue: evaluation in an in vivo rabbit model

Articular cartilage defects are a significant source of pain, have limited ability to heal, and can lead to the development of osteoarthritis. However, a surgical solution is not available. To tackle this clinical problem, non-degradable implants capable of carrying mechanical load immediately after implantation and for the duration of implantation, while integrating with the host tissue, may be viable option. But integration between articular cartilage and non-degradable implants is not well studied. Our objective was to assess the in vivo performance of a novel macroporous, nondegradable, polyvinyl alcohol construct. We hypothesized that matrix generation within the implant would be enhanced with partial digestion of the edges of articular cartilage. Our hypothesis was tested by randomizing an osteochondral defect created in the trochlea of 14 New Zealand white rabbits to treatment with: (i) collagenase or (ii) saline, prior to insertion of the implant. At 1 and 3-month post-operatively, the gross morphology and histologic appearance of the implants and the surrounding tissue were assessed. At 3 months, the mechanical properties of the implant were also quantified. Overall, the hydrogel implants performed favorably; at all time-points and in all groups the implants remained well fixed, did not cause inflammation or synovitis, and did not cause extensive damage to the opposing articular cartilage. Regardless of treatment with saline or collagenase, at 1 month post-operatively implants from both groups had a contiguous interface with adjacent cartilage and were populated with chondrocyte-like cells. At 3 months fibrous encapsulation of all implants was evident, there was no difference between area of aggrecan staining in the collagenase versus saline groups, and implant modulus was similar in both groups; leading us to reject our hypothesis. In summary, a porous PVA osteochondral implant remained well fixed in a short term in vivo osteochondral defect model; however, matrix generation within the implant was not enhanced with partial digestion of adjacent articular cartilage.     

Ionic liquids: a new class of sensing materials for detection of organic vapors based on the use of a quartz crystal microbalance

A QCM device employing ionic liquids as the sensing materials for organic vapors has been developed and evaluated. The sensing mechanism is based on the fact that the viscosity of the ionic liquid membrane decreases rapidly due to solubilization of analytes in the ionic liquids. This change in viscosity, which varies with the chemical species of the vapors and the types of ionic liquids, results in a frequency shift of the corresponding quartz crystal. The QCM sensor demonstrated a rapid response (average response time of less than 2 s) to organic vapors with an excellent reversibility because of the fast diffusion of analytes in ionic liquids. Furthermore, the ionic liquids, with zero vapor pressure and stable chemical properties, ensure a long-term shelf life for the sensor.     

Influence of synthetic parameters on the enhanced photocatalytic properties of ZnO nanoparticles for the degradation of organic dyes: a green approach

Herein, we report a green synthetic strategy using aqueous leaves extract of Actinodaphne madraspatna Bedd (AMB) for the synthesis of ZnO NPs. The physical shape, size, thermal stability, surface area, surface composition and chemical state, morphological and optical properties of the synthesized ZnO NPs are well characterized through UV–Visible diffuse reflectance spectroscopy (DRS UV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis–differential thermal analysis (TGA–DTA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photon spectroscopy (XPS). FT-IR spectrum of ZnO NPs showed a characteristic peak at 416.62 cm^?1. Optical studies of prepared ZnO NPs showed the bandgap values are reduced in the range of 3.05 to 2.96 eV. The XRD and TEM data revealed the synthesized ZnO NPs exist in wurtzite crystal structure with crystallite sizes of 18 nm to 68 nm range. The variation in bandgap, surface area and crystallite structure of ZnO NPs would be achieved by changing the experimental parameters. FESEM showed spherical-shaped structure. XPS result confirmed the atomic states of Zn and O. The green synthesized ZnO NPs were examined for the photocatalytic degradation of methylene blue (MB) and acid violet 17 (AV17) dyes under UV light and the rate constants ‘k’ was calculated. It is found that the green synthesized ZnO NPs with reduced bandgap showed enhanced photocatalytic activity with higher rate constant.

     

Self Organising Maps for variable selection: Application to human saliva analysed by nuclear magnetic resonance spectroscopy to investigate the effect of an oral healthcare product

SOMs (Self Organising Maps) are derived from the machine learning literature and serve as a valuable method for representing data. In this paper, the use of SOMs as a technique for determining the most significant variables (or markers) in a dataset is described. The method is applied to the NMR spectra of 96 human saliva samples, half of which have been treated with an oral rinse formulation and half of which are controls, and 49 variables consisting of bucketed intensities. In addition, three simulations, two of which consist of the same number of samples and variables as the experimental dataset and a third that contains a much larger number of variables, are described. Two of the simulations contain known discriminatory variables, and the remaining is treated as a null dataset without any specific discriminatory variables added. The described SOM method is contrasted to Partial Least Squares Discriminant Analysis, and a list of the markers determined to be most significant using both approaches was obtained and the differences arising are discussed. A SOM Discrimination Index (SOMDI) is defined, whose magnitude relates to how strongly a variable is considered to be a discriminator. In order to ensure that the model is stable and not dependent on the random starting point of the SOM, one hundred iterations were performed and variables that were consistently of high rank were selected. A variety of approaches for data representation are illustrated, and the main theoretical principles of employing SOMs for determining which variables are most significant are outlined. Software used in this paper was written in-house, allowing greater flexibility over existing packages, and tailored for the specific application in hand.     

The interaction of an atomic force microscope tip with a nano-object: a model for determining the lateral force

A calculation of the lateral force interaction between an atomic force microscope (AFM) tip and a nano-object on a substrate is presented. In particular, the case where the AFM tip is used to manipulate the nano-object is considered; i.e., the tip is displaced across the nano-object with the feedback off. The Hamaker equations are used to calculate the force when the tip and sample are not in contact and the Johnson, Kendall and Roberts (JKR) or Derjaguin, Muller and Toporov (DMT) formalisms are used for the contact force. The effect of the material parameters, the choice of contact theory and the shape of the nano-object on the resulting lateral forces are explored. The calculation is applied to an experimental system consisting of a cadmium selenide nanorod on graphite.     

Impact of scale on the effectiveness of disease control strategies for epidemics with cryptic infection in a dynamical landscape: an example for a crop disease.

We use a spatially explicit, stochastic model to analyse the effectiveness of different scales of local control strategies in containing the long-term, multi-seasonal spread of a crop disease through a dynamically changing population of susceptible crops in which there is cryptic infection. The model distinguishes between susceptible, infested and symptomatic fields. It is motivated by rhizomania disease on sugar beet in the UK as an exemplar of a spatially structured and partially asymptomatic epidemic. Our results show the importance of matching the scales of local control strategies to prevent intensification and regional spread of disease with the inherent temporal and spatial scales of an epidemic. A simple field-scale containment strategy, whereby the susceptible crop is no longer grown on fields showing symptoms, fails for this system with cryptic infection because the locally applied control lags behind the epidemic. A farm-scale strategy, whereby growers respond to the disease status of neighbouring farms by transferring their quota for sugar beet to farmers in regions of reduced risk, succeeds. We conclude that a soil-borne pathogen such as rhizomania could be managed by movement of susceptible crops in the landscape using a strategy that matches the temporal and spatial scales of the epidemic and which take account of risk aversion among growers. We show some parallels and differences in effectiveness between a 'culling' strategy involving crop removal around emerging foci and the local deployment of partially resistant varieties that reduce amplification and transmission of inoculum. Some relationships between the control of plant and livestock diseases are briefly discussed.     

Analysis of spatial resolution of an experiment on verification of the equivalence principle for a neutron by the diffraction method

Investigations of the spatial resolution of a setup for verification of the equivalence of inertial and gravitational masses of a neutron by the method of diffraction in a perfect crystal have been performed. Tests were conducted at Bragg angles of 74°–82°. A decrease in spatial resolution at Bragg angles >78° is detected.