S.K. Srivastava

Sensing mechanism in tin oxide-based thick-film gas sensors

A model has been developed for the sensing mechanism of metal oxide-based thick-film gas sensors. The model explains the behaviour of the sensor conductance as a function of the concentration of test gas and the operating temperature of the sensor. Using the Schottky-barrier conduction mechanism through grain boundaries, a relationship between the degree of surface coverage θ and the conductance G has been obtained. To relate the conductance with the concentration of the gas, the Freundlich adsorption isotherm for gases and vapours on a solid surface has been used. The isotherm relates the degree of surface coverage θ with the partial pressure of the gas (concentration). By eliminating θ, an expression relating the variation of G with concentration has been obtained. To study the validity of the model, a thick-film Pd-doped tin oxide gas sensor has been fabricated and tested with propanol (C3H7OH). The variation in the conductance with changes in concentration and temperature has been observed. The observed data show an excellent fit with the developed model. Using the experimental data, the constants of the theoretical equation have also been evaluated.

Sensing properties of palladium-gate MOS (Pd-MOS) hydrogen sensor-based on plasma grown silicon dioxide

Abstract This paper deals with the performance of a palladium-gate MOS hydrogen sensor studied by conductance method. Structure of the device was fabricated on a n-type 〈100〉 silicon wafer having resistivity of 1–6 Ω cm using plasma technology. Sensitivity and response–recovery time of the fabricated sensor have been studied for different concentration (1480–11 840 ppm) of hydrogen with varying signal frequency (500 Hz, 10 and 100 kHz) at room temperature. Hydrogen-induced interface-trapped density ( N it ) has been also evaluated as a function of gas concentration using a bias scan conductance method. Obtained results show that device performance is improved (i.e., high sensitivity and low response recovery time) and further it has been concluded that implementation of plasma technology (i.e., dry plasma cleaning of Si surface and in-situ RF anodization of Silicon in oxygen plasma near room temperature) may be a future step towards development of MOS-based sensors and integrated arrays with improved performance at room temperature.

Development of high sensitivity tin oxide based sensors for gas/odour detection at room temperature

Abstract An effort has been made to develop thick film tin oxide gas sensors which could detect various gases/odours at room temperature. To achieve this, the fabricated sensors were annealed in oxygen plasma for various durations. It was then found that, the room temperature sensitivity of such sensors was increased to about ten times as compared to the sensitivity of the non-annealed sensors. Further, plasma annealed sensors are found to be practically independent of temperature and the room temperature sensitivity of these sensors are found to be about 1.5 times the sensitivity of the conventional sensors at its operating temperature of 300°C. Studies on the variation of d.c. resistance, sensitivity, temporal response, current–temperature characteristics and impedance spectroscopy with the annealing time have also been made. These studies reveal that, with the increase in annealing time, there is a permanent gradual reduction in the d.c. resistance of annealed sensors. Further, it is also observed that with the increase in annealing time, the response time improves, barrier height reduces, barrier capacitance increases and the dependence of the sensitivity with temperature reduces while the sensitivity itself improves many-fold.

Identification of regulatory elements in 16S rRNA gene of Acinetobacter species isolated from water sample.

A bacterial strain, designated AcBz01, was isolated from a water sample collected from Gomti River, Lucknow, India, and identified using a molecular approach. On the basis of the bacterial 16S rRNA gene sequence phylogeny and comparison of this gene sequence with sequences in Ribosomal Database project II, evidence given in this study, it is proposed that isolate is closely related to members of the genus Acinetobacter. Identification and annotation of regulatory elements in the 16S rRNA gene and characterization of their interaction with the respective transcription factor can provide basis for better understanding of the mechanism of network of gene interaction of functionally related genes. The identification of such sites is relevant for locating promoter boundary of a gene and it also allows the prediction of specific gene expression pattern and response to disturbances in a known signaling pathway. Computational identification of regulatory elements and Transcription Factor with their binding sites in 16S rRNA gene of Acinetobacter sp. was performed using BPROM tool. We predicted the regulatory elements are TSS, -10 box, -35 box and three Transcription Factor (narP, ompR and fadR) with their binding sites in the upstream region of 16S rRNA gene of Acinetobacter sp. AcBz01. The GenBank accession number for 16S rRNA gene of Acinetobacter sp. AcBz01 is EU931637.

Identification of Escherichia coli through analysis of 16S rRNA and 16S-23S rRNA internal transcribed spacer region sequences

A bacterial strain, designated BzDS03 was isolated from water sample, collected from Dal Lake Srinagar. The strain was characterized by using 16S ribosomal RNA gene and 16S-23S rRNA internal transcribed spacer region sequences. Phylogenetic analysis showed that 16S rRNA sequence of the isolate formed a monophyletic clade with genera Escherichia. The closest phylogenetic relative was Escherichia coli with 99% 16S rRNA gene sequence similarity. The result of Ribosomal database projects classifier tool revealed that the strain BzDS03 belongs to genera Escherichia.16S rRNA sequence of isolate was deposited in GenBank with accession number FJ961336. Further analysis of 16S-23S rRNA sequence of isolate confirms that the identified strain BzDS03 be assigned as the type strain of Escherichia coli with 98% 16S-23S rRNA sequence similarity. The GenBank accession number allotted for 16S-23S rRNA intergenic spacer sequence of isolate is FJ961337.

The effect of hydrogen-induced interface traps on a titanium dioxide-based palladium gate MOS capacitor (Pd-MOSC): a conductance study

Abstract The conductance versus gate voltage response of a palladium-gate MOS capacitor with 0.5 μm of TiO 2 (oxide layer) has been studied as a function of hydrogen gas concentration and signal frequency. The structure of the device was completed by evaporating titanium dioxide over p 〈111〉-type silicon wafer (cleaned as per standard silicon technology) having a resistivity of 3–5 Ω cm and subsequent palladium front with aluminium back metallization. The G - V response of the fabricated MOS capacitor was studied on exposure to hydrogen in Ar ambient. The fabricated device is sensitive to hydrogen (1–3%) at room temperature. The interface state density ( D it ) was determined at the surface potential corresponding to the peak in the conductance curve, using a bias scan conductance method at fixed frequency. It was found that D it increases with an increase in hydrogen gas concentration. Further, it has been observed that a change in conductance is better at lower frequencies, which may be due to the balanced communication of interface traps with the valance and conduction bands of silicon substrate.

Identification of Comamonas species using 16S rRNA gene sequence.

A bacterial strain Bz02 was isolated from a water sample collected from river Gomti at the Indian city of Lucknow. We characterized the strain using 16S rRNA sequence. Phylogenetic analysis showed that the strain formed a monophyletic clade with members of the genus Comamonas. The closest phylogenetic relative was Comamonas testosteroni with 95% 16S rRNA gene sequence similarity. It is proposed that the identified strain Bz02 be assigned as the type strain of a species of the genus Comamonas (Comamonas sp Bz02) based on 16S rRNA gene sequence search in Ribosomal Database Project, small subunit rRNA and large subunit rRNA databases together with the phylogenetic tree analysis. The sequence is deposted in GenBank with the accession number FJ211417.

Virtual screening and pharmacophore studies for ftase inhibitors using Indian plant anticancer compounds database.

Farnesyl transferase (FTase) is an enzyme responsible for post-translational modification in proteins having a carboxy-terminal CaaX motif in human. It catalyzes the attachment of a lipid group in proteins of RAS superfamily, which is essential in signal transduction. FTase has been recognized as an important target for anti cancer therapeutics. In this work, we performed virtual screening against FTase with entire 125 compounds from Indian Plant Anticancer Database using AutoDock 3.0.5 software. All compounds were docked within binding pocket containing Lys164, Tyr300, His248 and Tyr361 residues in crystal structure of FTase. These complexes were ranked according to their docking score, using methodology that was shown to achieve maximum accuracy. Finally we got three potent compounds with the best Autodock docking Score (Vinorelbine: -21.28 Kcal/mol, Vincristine: -21.74 Kcal/mol and Vinblastine: -22.14 Kcal/mol) and their energy scores were better than the FTase bound co-crystallized ligand (L- 739: ―7.9 kcal/mol). These three compounds belong to Vinca alkaloids were analyzed through Python Molecular Viewer for their interaction studies. It predicted similar orientation and binding modes for these compounds with L-739 in FTase.Thus from the complex scoring and binding ability it is concluded that these Vinca alkaloids could be promising inhibitors for FTase. A 2-D pharmacophore was generated for these alkaloids using LigandScout to confirm it. A shared feature pharmacophore was also constructed that shows four common features (one hydogen bond Donar, Two hydrogen bond Acceptor and one ionizable area) help compounds to interact with this enzyme.

Influence of longitudinal electric field on vapour deposited thin films of cadmium sulphide—a report

Abstract In this report we give a brief account of the various processes of the formation of thin films. This is followed by a description of the influence of various deposition parameters on the characteristic properties of thin films. The electrical and structural characterization of vapour deposited cadmium sulphide films grown under the influence of electric fields is discussed. This article is a compilation of the previous reported results. Various observations (viz. conductivity measurement, thermoelectric power measurement X-ray observation and crossover voltage measurement) suggest that there is an increase in disorderliness (as a result of freezing in action) due to application of a dc electric field at the time of growth of the film.

A ClpP protein model as tuberculosis target for screening marine compounds

ATP-dependent Clp protease (ClpP) is a core unit of a major bacterial protease complex employing as a new attractive drug target for that isolates, which are resistant to antibiotics. Mycobacterium tuberculosis, a gram-positive bacterium, is one of the major causes of hospital acquired infections. ClpP in Mycobacterium tuberculosis is usually tightly regulated and strictly requires a member of the family of Clp-ATPase and often further accessory proteins for proteolytic activation. Inhibition of ClpP eliminates these safeguards and start proteolytic degradation. Such uncontrolled proteolysis leads to inhibition of bacterial cell division and eventually cell death. In order to inhibit Clp protease, at first three dimensional structure model of ClpP in Mycobacterium tuberculosis was determined by comparative homology modeling program MODELLER based on crystal structure of the proteolytic component of the caseinolytic Clp protease (ClpP) from E. coli as a template protein and has 55%sequence identity with ClpP protein. The computed models energy was minimized and validated using PROCHECK to obtain a stable model structure and is submitted in Protein Model Database (PMDB-ID: PM0075741). Stable model was further used for virtual screening against marine derived bioactive compound database through molecular docking studies using AutoDock 3.05. The docked complexes were validated and enumerated based on the AutoDock Scoring function to pick out the best marine inhibitors based on docked Energy. Thus from the entire 186 Marine compounds which were Docked, we got best 5 of them with optimal docked Energy (Ara-A: -14.31 kcal/mol, Dysinosin C: - 14.90kcal/mol, Nagelamide A: -20.49 kcal/mol, Strobilin: -8.02 kcal/mol, Manoalide: -8.81 kcal/mol). Further the five best-docked complexes were analyzed through Python Molecular Viewer software for their interaction studies. Thus from the Complex scoring and binding ability its deciphered that these Marine compounds could be promising inhibitors for ClpP as Drug target yet pharmacological studies have to confirm it.