Vipul Singh

Improvement in glucose biosensing response of electrochemically grown polypyrrole nanotubes by incorporating crosslinked glucose oxidase.

In this paper a novel enzymatic glucose biosensor has been reported in which platinum coated alumina membranes (Anodisc™s) have been employed as templates for the growth of polypyrrole (PPy) nanotube arrays using electrochemical polymerization. The PPy nanotube arrays were grown on Anodisc™s of pore diameter 100 nm using potentiostatic electropolymerization. In order to optimize the polymerization time, immobilization of glucose oxidase (GOx) was first performed using physical adsorption followed by measuring its biosensing response which was examined amperometrically for increasing concentrations of glucose. In order to further improve the sensing performance of the biosensor fabricated for optimum polymerization duration, enzyme immobilization was carried out using cross-linking with glutaraldehyde and bovine serum albumin (BSA). Approximately six fold enhancement in the sensitivity was observed in the fabricated electrodes. The biosensors also showed a wide range of linear operation (0.2-13 mM), limit of detection of 50 μM glucose concentration, excellent selectivity for glucose, notable reliability for real sample detection and substantially improved shelf life.

Influence of potassium permanganate on the anisotropic growth and enhanced UV emission of ZnO nanostructures using hydrothermal process for optoelectronic applications

The effect of in situ addition of potassium permanganate (KMnO4) in controlling morphology, composition, structural and optical properties of the ZnO nanostructures prepared by hydrothermal technique has been investigated. The influence of synthesis conditions on the growth of ZnO nanorods was meticulously studied by field-emission scanning electron microscope, X-ray diffractometer, transmission electron microscopy (TEM) and high-resolution TEM. It is demonstrated that the KMnO4 concentration has great influence on the morphology and on the alignment of ZnO nanorods. Further the optical properties of nanostructures were investigated by photoluminescence (PL) spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy. The PL spectrum divulged a continuous suppression of defect-related broadband emission by increasing the concentration of the KMnO4, which produced the quenching of surface defects present in the nanorods. The intensity ratio of the peaks corresponding to near-band emission (NBE) to that of deep-level emission of the KMnO4-modified ZnO nanorods was found to increase by eightfold of magnitude. Further it must be noted that nearly 17-fold enhancement in the PL emission of the peak corresponding to NBE was observed in KMnO4-modified ZnO compared to the ZnO grown without any additive. The I–V plot showed dependence of current values under dark and illumination over the amount of KMnO4 added during the growth stage.Graphical Abstract

Improved Photoresponse of Hybrid ZnO/P3HT Bilayered Photodetector Obtained Through Oriented Growth of ZnO Nanorod Arrays and the Use of Hole Injection Layer

We report highly oriented one-dimensional (1-D) growth of zinc oxide (ZnO) nanorod arrays (NRA) which were later utilized to fabricate hybrid photodiodes having the typical photodiode configuration of indium tin oxide (ITO)/ZnO/poly(3-hexylthiophene) (P3HT)/Ag. These functional hybrid bilayered photodiodes were found to have high rectification ratio under dark conditions and demonstrated enhanced responsivity under light illumination. Further, we studied the effect of an intermediate electron blocking layer of poly(ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) on the photodiode characteristics and demonstrated ITO/ZnO/P3HT/PEDOT:PSS/Ag photodiodes, reporting very high rectification ratio and responsivity in this bilayered configuration. The observed results are explained on the basis of the increased surface area of contact between the ZnO nanorods and the P3HT, and also the efficient hole injection into the P3HT layer from the top Ag electrode.

Enhancement of ZnO-based flexible nano generators via a sol–gel technique for sensing and energy harvesting applications

Zinc oxide (ZnO) is a remarkable inorganic semiconductor with exceptional piezoelectric properties compared to other semiconductors. However, in comparison to lead-based hazardous piezoelectric materials, its features have undesired limitations. Here we report the 5~6 folds enhancement in the piezoelectric properties via chemical doping of copper matched to intrinsic ZnO. The flexible piezoelectric nanogenerator (F-PENG) device was fabricated using an unpretentious solution process of spin coating with other advantages like robust, low weight, improved adhesion, and low cost. The devices were used to demonstrate energy harvesting from a Standard weight as low as 4 gm and can work as a self-powered mass sensor in a broad range of 4 to 100 gm. The device exhibited a novel energy harvesting technique from a wind source due to its inherent flexibility. At three different velocities (10~30 m/s) and five different angles of attack (0~180 degrees), the device validated the ability to discern different velocities and directions of flow. The device will be useful for mapping the flow of air apart from harvesting the energy. The simulation was done to verify the underlining mechanism of aerodynamics involved in it.Zinc oxide (ZnO) is a remarkable inorganic semiconductor with exceptional piezoelectric properties compared to other semiconductors. However, in comparison to lead-based hazardous piezoelectric materials, its properties have undesired limitations. Here we report a 5∼6 fold enhancement in piezoelectric features via chemical doping of copper matched to intrinsic ZnO. A flexible piezoelectric nanogenerator (F-PENG) device was fabricated using an unpretentious solution process of spin coating, with other advantages such as robustness, low-weight, improved adhesion, and low cost. The device was used to demonstrate energy harvesting from a standard weight as low as 4 gm and can work as a self-powered mass sensor in a broad range of 4 to 100 gm. The device exhibited a novel energy harvesting technique from a wind source due to its inherent flexibility. At three different velocities (10∼30 m s-1) and five different angles of attack (0∼180 degrees), the device validated the ability to discern different velocities and directions of flow. The device will be useful for mapping the flow of air apart from harvesting the energy. The simulation was done to verify the underlining mechanism of aerodynamics involved.

Insights into non-noble metal based nanophotonics: exploration of Cr-coated ZnO nanorods for optoelectronic applications

Herein, the room temperature photoluminescence and Raman spectra of hydrothermally grown ZnO nanorods coated with Cr are investigated for optoelectronic applications. A thorough examination of the photoluminescence spectra of Cr coated ZnO nanorods showed the suppression of deep level emissions by more than twenty five times with Cr coating compared to that of pristine ZnO nanorods. Moreover, the underlying mechanism was proposed and can be attributed to the formation of Schottky contacts between Cr and ZnO resulting in defect passivation, weak exciton–plasmon coupling, enhanced electric field effect and formation of hot carriers due to interband transitions. Interestingly, with the increase in sputtering time, the ratio of the intensities corresponding to the band gap emission and deep level emission was observed to increase from 6.2 to 42.7, suggesting its application for UV only emission. Further, a planar photodetector was fabricated (Ag–ZnO–Ag planar configuration) and it was observed that the dark current value got reduced by more than ten times with Cr coating, thereby opening up its potential for transistor applications. Finally, Cr coated ZnO nanorods were employed for green light sensing. Our results demonstrated that ZnO nanorods decorated with Cr shed light on developing stable and high-efficiency non-noble metal based nanoplasmonic devices such as photodetectors, phototransistors and solar cells.

Investigations on transformer oil temperature sensing using CuAlNi/polyimide shape memory alloy composite film

Power transformer is the one of the largely important as well as one of the costly elements in the electricity grid. Any malfunction of this element may affect the reliability of the entire network and could have considerable economic impact on the system. For several reasons, overloading of power transformers beyond their rating has been reported frequently. The primary issue leading to the failure of transformer is contamination of transformer oil by the working components due to prolonged high temperature exposure. Transformer oil temperature can be utilized as a primary parameter in monitoring the life of the transformer. At present, electrical approach are vulnerable to electromagnetic interference and are limited by sensors lifetime. Other non-contact techniques are ineffective due to difficulties in processing the output signal. In this work a CuAlNi/Polyimide shape memory alloy composite has been applied to act as a temperature sensor in mineral oils. The composite film has been developed through thermal evaporation which exhibited two-way displacement without and post-processing and training. The developed films are employed in a custom made oil rig and the suitability of using it as a circuit breaker in temperature sensing application has been probed. The circuit breaker can be triggered by measuring the displacement of the bimorph using laser displacement sensor. The measurement is of noncontact type and the temperature can be monitored at regular intervals. For comparison a procure Nickel-Titanium spring with transformation temperature less than 100 °C is also used for the studies. The results show that the developed bimorphs has good sensitivity of 0.2 mm/°C and the output displacement is significant. Further the effect of contamination in the mineral oils is also probed by adding known amounts of impurities and the ageing effect has been studied. A higher resolution measuring system using interferometry has been proposed.

Effect of immobilization technique on performance ZnO nanorods based enzymatic electrochemical glucose biosensor

In this paper, ZnO Nanorods (ZNR) have been synthesized over Platinum (Pt) coated glass substrate with in-situ addition KMnO4 during hydrothermal growth process. Significant variation in ZnO nanostructures was observed by KMnO4 addition during the growth. Glucose oxidase was later immobilized over ZNRs. The as-prepared ZNRs were further utilized for glucose detection by employing amperometric electrochemical transduction method. In order to optimize the performance of the prepared biosensor two different immobilization techniques i.e. physical adsorption and cross linking have been employed and compared. Further investigations suggest that immobilization via cross linking method resulted in the improvement of the biosensor performance, thereby significantly affecting the sensitivity and linear range of the fabricated biosensor. Among the two types of biosensors fabricated using ZNR, the best performance was shown by cross linked electrodes. The sensitivity for the same was found to be 17.7 mA-cm-2-M-1, along with a wide linear range of 0.5-8.5 mM.

Structural and optoelectronic characterization of organic vapor phase deposited thin films of oriented DH6T molecules

Growth and orientation of the molecules in thermally evaporated thin films of α, ω-Dihexylsexithiophene (DH6T) on oxidized Si (100) substrate have been investigated. XRD studies revealed that grown thin films are crystalline with monoclinic structure. Polarized photoluminescence studies further revealed that the molecules in the grown thin films are oriented vertically at an angle of 32.68° with respect to the substrate normal. AFM images showed a step like circular structure with domain size and step height ∼800-1000 nm and 3-4nm respectively. The observed step height was approximately equal to molecule length of DH6T, which also suggested that the molecules adopt a standing orientation.

Influence of laser parameters in generating the NiTi nanoparticles with a rotating target using underwater solid state Nd: YAG laser ablation

The great effort that the scientific community has put in the last decade in the study of nanoscience and nanotechnology has been leading the research toward the development of new methodologies of nanostructures synthesis. Among them, Pulsed Laser Ablation in Liquid, PLAL, is gaining an increasing interest thanks to several promising advantages, which include: environmental sustainability, easy experimental set-up (which does not require extreme conditions of the ambient of synthesis), long-lasting stability of the nanoparticles, which are produced completely free of undesired contaminants or dangerous synthesis reactants. In this work, a drop wise flow of deionized water on the periphery of NiTi rotating target was tested as a procedure for the significant production of NiTi nanoparticles. This is a novel technique to improve the ablation efficiency of nanoparticles than the existing techniques of laser ablation. The influence of varying external parameters like laser wavelengths and laser fluences on the size distribution of nanoparticle was investigated. Second harmonic and third harmonics of Nd: YAG nanosecond laser with three different laser fluences of 30 J/cm2, 40 J/cm2 and 50 J/cm2 was used to ablate the nitinol (Ni-55%, Ti-45%) target. The average particle size and redistribution was characterized by dynamic light scattering (DLS) and the crystalline formation of NiTi nanoparticles were analyzed by X-ray diffraction, where it confirms the alloy formation of NiTi nanoparticles.

Parametric investigation of substrate temperatures on the properties of Zinc oxide deposited over a flexible polymeric substrate via spray technique

Here we report the influence of substrate temperature (300-500 °C) on the deposition and growth of ZnO over a Flexible polyimide film. Owing to its simplicity, large area deposition capability and Cost effectivity Spray Pyrolysis technique was used. We have modified the conventional process of Spray pyrolysis by spraying for shorter durations and repeating the process which in turn reduced the Island formation of ZnO. Moreover, this technique helped in maintaining the constant temperature and uniformity during the deposition as prolonged spraying reduces the temperature of the heating plate drastically. Photoluminescence (PL) reveals that at 350 and 400° C the defect have reduced. XRD reveals the crystallinity and Impurities present. FE-SEM reveals the structure morphology changes with the change in the substrate temperature. TGA was done to ensure that substrate does not undergoes dissociation at high temperature. It was observed at the film deposited at 400 °C was found to be more uniform, defect free and crystalline. Hence, IV characterization of the film deposited at 400 °C was done which showed good rectification behaviour of the Schottky diodes.