Structural characteristics,fluorescence quenching,and antioxidant activity of the arabinogalactan protein-rich fraction from senna (<Emphasis Type="Italic">Cassia angustifolia</Emphasis>) leaves

Senna (Cassia angustifolia) is widely used in Indian folk medicine for the prevention of various disorders. Herein, we have demonstrated that water extracted arabinogalactan protein (AGP) rich fraction possesses strong antioxidative activity. The AGP rich fraction was analyzed using chemical, chromatographic, and spectroscopic methods. Effect of water extracted polymers on bovine serum albumin spectrum was determined using excitation wavelength of 282 nm. The antioxidant capacity of this fraction was studied by ferric reducing antioxidant power (FRAP) and DPPH radical assays. This polymeric fraction, ≥88% of which gets precipitated with Yariv reagent, consisted mainly of (1→5)-/(1→3,5)-linked α-arabinosyl, (1→3)-/(1→3,6)-linked-galactosyl residues and terminal arabinofuranosyl residues. Its in vitro antioxidant capacity is comparable to that of standard antioxidants. Fluorescence quenching studies furnishes evidence for the interaction of the arabinogalactan protein with bovine serum albumin.     

Label-Free Detection of Protein interactions with peptide aptamers by open circuit potential measurement

Label-free electrical detection of protein interactions has been achieved by direct measurement of variations in open circuit potential (OCP) using an accurate differential voltage measurement. Our model system involves a panel of peptide aptamers that recognise specific protein partners of the cyclin-dependent kinase (CDK) family.Different peptide aptamers immobilized on gold electrodes were used for the detection of human CDK2 and CDK4. The formation of the peptide aptamer recognition layer and the efficiency of its interaction with CDK proteins in yeast cell lysates were characterized by quartz crystal microbalance measurements. The interaction of the peptide aptamers with CDK proteins was successfully detected by direct OCP measurements. The OCP dependence on the pH of the measurement buffer confirms that the effects observed are due to the change in charge upon protein interaction. Variations in charge transfer resistance and in protein/double-layer capacitance were investigated by means of electrochemical impedance spectroscopy with charged redox markers in solution.The present work shows that electrical detection of protein interactions can be achieved by direct measurement of OCP variations using suitable differential voltage instrumentation. The results indicate that label-free detection of protein interactions is possible with potentiometric transducers such as field-effect transistors.     

Numerical predictions of backward-facing step flows in microchannels using extended Navier–Stokes equations

Flows in microchannels were successfully predicted, in the past, both analytically and numerically, employing the extended Navier–Stokes equations (ENSE). In ENSE, the self-diffusion transport of mass, together with the resulting momentum and heat transport, is taken into account properly and the same is omitted in the classical Navier–Stokes equations. The ENSE have been employed here to numerically predict backward-facing step flows in microchannels, and the predictions are summarized in this paper. The results obtained by employing ENSE are compared with the available literature data computed by both direct simulation Monte Carlo and slip-velocity-based simulations. The good agreement of the present results with those given in the literature evidently points out that the ENSE can be applied to gas flows through complex microchannel geometries.     

Development of a membrane-based immunofiltration assay for the detection of T-2 toxin

An improved analytical device capable of performing simultaneous immunofiltration-based immunoassay on 30 samples in the presence of reference standards has been developed. The device consists of a rectangular membrane with 36 antibody spotted zones, one end of which was attached to a semirigid polyethylene card. A piece of wetted filter paper between the membrane and the polyethylene card absorbs the added reagent. The assay is a competitive one using T-2 toxin-horseradish peroxidase (T-2 toxin-HRP) as the labeled analyte and 4-chloro-1 naphthol (4CN) as the substrate. Signal amplification was done by the Super-CARD signal amplification method. Semiquantitative results were obtained by visual comparison of the color intensity of a sample spot with those of reference standards. Densitometric analysis was used for quantitation. The method allows rapid and easy determination of T-2 toxin in wheat and poultry feed with detection limits of 12.5 and 25 microg x kg(-)(1), respectively, with accuracy and precision. Matrix interference was eliminated by appropriate dilution of sample extracts with assay buffer. The detection sensitivity in ELISA was 10-fold higher than that in the membrane-based method. Noninfected samples were spiked with T-2 toxin at several concentrations and analyzed by the present method and rapid ELISA. Mean recoveries by both methods were between 80 and 108%. The correlation between the two methods was excellent (R(2) = 0.99).     

In situ sample cleanup during immunoassay: a simple method for rapid detection of aflatoxin B, in food samples

A strategy for rapid in situ elimination of interfering substances that are present in extracts of food samples during assay is described in this article. The novel feature of this method is that the sample purification is carried out as a part of the assay, and a separate sample cleanup step is not required. The assay procedure involves the sequential addition of standard or sample, cleaning solutions, and aflatoxin B1-horseradish peroxidase conjugate (AFB1-HRP) over antibody-spotted zones of a membrane, and 3,3'-diaminobenzidine was used as the substrate for visualization. We have determined that trifluoroacetic acid and propionic acids at concentrations of 100 mM are highly effective for cleaning groundnut, wheat, corn, and poultry feed samples and that NaHCO3 (100 mM) is successful in cleaning processed soybean. In all cases, subsequent washing was performed with phosphate-buffered saline solution to facilitate the removal of traces of adhering interfering substances. A batch of 12 samples can be analyzed within 8 min either by visual comparison of the color intensity (inversely related to the analyte concentration) of a sample spot with those of reference standards or, more precisely, by densitometry. The method was tested for the analysis of AFB1 in groundnut, wheat, corn, processed soybean, chili, and poultry feed. The detection limit obtained was 5 microg/kg, except for chili, where it was 10 microg/kg. The average recoveries from different noninfected food samples spiked with AFB1 at concentrations of 5 to 100 microg/kg were between 99 and 105%. The values obtained for infected corn and groundnut samples correlated well with the estimates obtained by high-pressure liquid chromatography. The absence of a sample extraction step reduces the cost and labor involved in the assay. The method may be potentially applicable to the assay of other mycotoxins and environmental pollutants.     

Temperature-induced unfolding pathway of a type III antifreeze protein: insight from molecular dynamics simulation

Molecular dynamics simulations of the temperature-induced unfolding reaction of a cold-adapted type III antifreeze protein (AFPIII) from the Antarctic eelpout Lycodichthys dearborni have been carried out for 10 ns each at five different temperatures. While the overall character and order of events in the unfolding process are well conserved across temperatures, there are substantial differences in the timescales over which these events take place. Plots of backbone root mean square deviation (RMSD) against radius of gyration (Rg) serve as phase space trajectories. These plots also indicate that the protein unfolds without many detectable intermediates suggestive of two-state unfolding kinetics. The transition state structures are identified from essential dynamics, which utilizes a principal component analysis (PCA) on the atomic fluctuations throughout the simulation. Overall, the transition state resembles an expanded native state with the loss of the three 3₁₀ helices and disrupted C-terminal region.Our study provides insight into the structure–stability relationship of AFPIII, which may help to engineer AFPs with increased thermal stability that is more desirable than natural AFPs for some industrial and biomedical purposes.     

Edge-Fitting Based Energy Detection for Cognitive Radios

Two well-known drawbacks of energy detection sensing are its poor performance at low SNR and dependency on the accurate knowledge of noise power. To overcome these challenges in the context of wideband sensing, this paper proposes a spectrum sensing algorithm, inspired from edge detection techniques used in image processing. It is an improved, detailed and extended version of the gradient based method reported earlier (Koley et al. IEEE Communications Letters 19, 391–394, 2015). It is characterized by (i) histogram based noise power estimation for dynamic threshold computation (ii) preprocessing to obtain high detection probability with fewer numbers of samples and (iii) use of edge values as decision metric. Monte Carlo simulations as well as real-time wideband-sensed data captured through a Universal Software Radio Peripheral (USRP) is used to evaluate the performance of the algorithm. Mathematical formulations for the position of “SNR wall” and detection performance at different signal bandwidths is derived. Computational complexity of the edge-fitting scheme is shown to be lower than some of the wavelet approaches.     

Comparison of Properties of Pristine and 200 MeV Ag15+ Ions Irradiated ‘Li’ 3 wt% Doped V2O5 Thin Films

Lithium (3 wt%) doped V₂O₅ thin film of thickness 97 nm was spray deposited over an ITO coated glass substrate at 450 °C. The deposited film was irradiated with 200 MeV Ag¹⁵⁺ swift heavy ions (SHI) at a fluence of 5 × 10¹² ions/cm². X-ray diffraction reveals the pristine and irradiated films to have an orthorhombic phase. The SHI irradiation induced thermal spike lead to texturing along the (400) direction along with partial amorphization. The 394 cm^?1 O–V–O Raman bending deformation is suppressed due to SHI irradiation induced oxygen vacancies. Optical transparency decreased from 80 to 50 % and the direct and indirect band gaps showed red shift upon SHI irradiation. Hall effect study revealed marginal variation in transport parameters upon SHI irradiation. The results are discussed.