Zakir Hussain

Enhanced mechanical, thermal and antimicrobial properties of poly(vinyl alcohol)/graphene oxide/starch/silver nanocomposites films

In the present work, synthesis of poly(vinyl alcohol)/graphene oxide/starch/silver (PVA/GO/Starch/Ag) nanocomposites films is reported. Such films have been characterized and investigated for their mechanical, thermal and antimicrobial properties. The exfoliation of GO in the PVA matrix occurs owing to the non-covalent interactions of the polymer chains of PVA and hydrophilic surface of the GO layers. Presence of GO in PVA and PVA/starch blends were found to enhance the tensile strength of the nanocomposites system. It was found that the thermal stability of PVA as well as PVA/starch blend systems increased by the incorporation of GO where strong physical bonding between GO layers and PVA/starch blends is assumed to cause thermal barrier effects. Antimicrobial properties of the prepared films were investigated against Escherichia coli and Staphylococcus aureus. Our results show enhanced antimicrobial properties of the prepared films where PVA-GO, PVA-Ag, PVA-GO-Ag and PVA-GO-Ag-Starch showed antimicrobial activity in ascending order.

FTIR Study of the Photoinduced Processes of Plant Phytochrome Phya using Isotope-Labeled Bilins and Density Functional Theory Calculations

Fourier transform infrared spectroscopy was used to analyze the chromophore structure in the parent states Pr and Pfr of plant phytochrome phyA and the respective photoproducts lumi-R and lumi-F. The spectra were obtained from phyA adducts assembled with either uniformly or selectively isotope-labeled phytochromobilin and phycocyanobilin. The interpretation of the experimental spectra is based on the spectra of chromophore models calculated by density functional theory. Global (13)C-labeling of the tetrapyrrole allows for the discrimination between chromophore and protein bands in the Fourier transform infrared difference spectra. All infrared difference spectra display a prominent difference band attributable to a stretching mode with large contributions from the methine bridge between the inner pyrrole rings (B-C stretching). Due to mode coupling, frequencies and isotopic shifts of this mode suggest that the Pr chromophore may adopt a distorted ZZZssa or ZZZasa geometry with a twisted A-B methine bridge. The transition to lumi-R is associated with only minor changes of the amide I bands indicating limited protein structural changes during the isomerization site of the C-D methine bridge. Major protein structural changes occur upon the transition to Pfr in which the chromophore adopts a ZZEssa or ZZEasa-like state. In addition, specific interactions with the protein alter the structure of the B-C methine bridge as concluded from the substantial downshift of the respective stretching mode. These interactions are removed during the photoreaction to lumi-F (ZZE-->ZZZ), which involves only small protein structural changes.

Liquid crystals based sensing platform-technological aspects

In bulk phase, liquid crystalline molecules are organized due to non-covalent interactions and due to delicate nature of the present forces; this organization can easily be disrupted by any small external stimuli. This delicate nature of force balance in liquid crystals organization forms the basis of Liquid-crystals based sensing scheme which has been exploited by many researchers for the optical visualization and sensing of many biological interactions as well as detection of number of analytes. In this review, we present not only an overview of the state of the art in liquid crystals based sensing scheme but also highlight its limitations. The approaches described below revolve around possibilities and limitations of key components of such sensing platform including bottom substrates, alignments layers, nature and type of liquid crystals, sensing compartments, various interfaces etc. This review also highlights potential materials to not only improve performance of the sensing scheme but also to bridge the gap between science and technology of liquid crystals based sensing scheme.

Ultra fast polymer network blue phase liquid crystals

Polymer-stabilization of blue phase liquid crystal systems within a host polymer network are reported, which enables ultrafast switching flexible displays. Our newly developed method to stabilize the blue phase in an existing polymer network (e.g., that of a polymer network liquid crystal; PNLC) has shown wide temperature stability and fast response speeds. Systems where the blue phase is stabilized in an already existing polymer network are attractive candidates for ultrafast LCDs. The technology also promises to be applied to flexible PNLC and/or polymer dispersed liquid crystal (PDLC) displays using plastic substrate such as polyethylene terephthalate (PET).

Graphene oxide — A platform towards theranostics

Due to the abundance of its utilization in various applications, ranging from electronics to biomedicine, recent data witnessed manifold increase in the commercial potential of graphene oxide based biomaterials. Major contribution of such increased potential comes from the work on graphene oxide which carries unparalleled advantage over graphene itself and/or reduced graphene oxide. Few reviews have been published in previous years which have highlighted the capacity of graphene oxide in drug delivery and photothermal therapy application. But this review exclusively provides an outlook for the role of graphene oxide based magnetic composites in constituting a theranostic system through previously inaccessible options. These composites have been exploited for their use in drug delivery applications, biosensing, bioimaging and phototherapy. This review discusses the potential challenges and advantages of using graphene oxide based magnetic nanocomposites systems to explore much needed length and breadth of theranostics, not fully elaborated so far.

Liquid crystal based sensors monitoring lipase activity: A new rapid and sensitive method for cytotoxicity assays

In this work we present liquid crystal (LC) based sensor devices to monitor cell viability. The sensing layer is composed by the LC and a planar monolayer of phospholipids. In the presence of minute traces of phospholipases, which hydrolyze enzymatically phospholipids, the LC-lipid interface is disintegrated. This event causes a change in orientation of the LC, which was followed in a polarized microscope. The lipase activity can be used to measure the cell viability, since members of this enzyme family are released by cells, as they undergo necrosis. The described sensor was used to monitor the presence of the lipases released from three different cell lines, which were either exposed to highly cytotoxic model compounds (sodium azide and paracetamol) or subjected to freeze-thaw cycles to induce cell death by a non-chemical based inducer for apoptosis, such as temperature. Finally, the comparison of lipase activity detected by a state-of-the-art fluorescence assay to the LC based system resulted in the superiority of the LC system concerning incubation time and sensitivity.

Low resistivity ZnO-GO electron transport layer based CH3NH3PbI3 solar cells

Perovskite based solar cells have demonstrated impressive performances. Controlled environment synthesis and expensive hole transport material impede their potential commercialization. We report ambient air synthesis of hole transport layer free devices using ZnO-GO as electron selective contacts. Solar cells fabricated with hole transport layer free architecture under ambient air conditions with ZnO as electron selective contact achieved an efficiency of 3.02%. We have demonstrated that by incorporating GO in ZnO matrix, low resistivity electron selective contacts, critical to improve the performance, can be achieved. We could achieve max efficiency of 4.52% with our completed devices for ZnO: GO composite. Impedance spectroscopy confirmed the decrease in series resistance and an increase in recombination resistance with inclusion of GO in ZnO matrix. Effect of temperature on completed devices was investigated by recording impedance spectra at 40 and 60 oC, providing indirect evidence of the performance of solar cells at elevated temperatures.

Investigation of reactive acrylic monomers for their effect on the temperature range and operating voltage of polymer-stabilised optically isotropic liquid crystal blue phases

Synthesis of various reactive acrylic monomers (RMs) to be used as components in liquid crystalline blue phase (LCBP) mixtures has been carried out in order to investigate their effect on temperature range and operating voltage. All the newly synthesised RMs were fully purified and characterised. These were added in various molar ratios to LCBP mixtures, which were stabilised by ultraviolet polymerisation, and improvements in the operating voltage and temperature range were studied. The compatibility of LCBP and monomer side-chains was investigated in terms of polarity and alkyl chain length.

Effect of long flexible chain reactive monomers on the operating voltage of optically isotropic blue phase liquid crystals

A reduction in operating voltage and switch-off time of polymer-stabilised blue phase (BP) liquid crystals has been achieved using reactive monomers (RMs) with long flexible alkyl side-chains. In place of a standard RM, two groups of novel RMs with and without alkyl side-chains have been synthesised. Polymer-stabilised BP systems were obtained by polymerising these RMs using UV irradiation, and their electro-optical properties were compared. Analysis of the results has provided molecular guidelines for future synthesis. The new RMs were purified and characterised chemically.

Advances in biogenic synthesis of palladium nanoparticles

Green approaches for the synthesis of nanoparticles provide advantages due to the fact that green protocols are benign and environmentally friendly. Among various green recipes, biogenic synthesis of nanoparticles has recently emerged as an active area of research due to the simplicity of this method, with cost effective protocols, higher potential of reduction and low toxic effect on human health and the environment. Moreover, the biogenic reduction occurs at physiological conditions of temperature and pressure. The raw materials are easily available and therefore, the reaction can easily be scaled up. This paper presents a review to give an idea about the most reliable, cost-effective and environment friendly synthetic protocols for metal nanoparticles to control size, shape and dispersity. In this contribution, we have emphasized particularly various plants responsible, and investigated so far, for the synthesis of palladium nanoparticles. Based on the isolated compounds/metabolites such as polyols, polyphenols, flavonoids and proteins from the respective plant extracts, a correlation is established where such metabolites are linked with the biogenic syntheses of Pd nanoparticles. The present investigation and works reviewed lead us to recommend a few potential plants for the reduction of Pd2+ ions into Pd0 nanoparticles. This review not only summarizes the present literature but also highlights the potential of this field to open up new avenues for researchers.