Arun Banpurkar

Biosurfactants, bioemulsifiers and exopolysaccharides from marine microorganisms

Marine biosphere offers wealthy flora and fauna, which represents a vast natural resource of imperative functional commercial grade products. Among the various bioactive compounds, biosurfactant (BS)/bioemulsifiers (BE) are attracting major interest and attention due to their structural and functional diversity. The versatile properties of surface active molecules find numerous applications in various industries. Marine microorganisms such as Acinetobacter, Arthrobacter, Pseudomonas, Halomonas, Myroides, Corynebacteria, Bacillus, Alteromonas sp. have been studied for production of BS/BE and exopolysaccharides (EPS). Due to the enormity of marine biosphere, most of the marine microbial world remains unexplored. The discovery of potent BS/BE producing marine microorganism would enhance the use of environmental biodegradable surface active molecule and hopefully reduce total dependence or number of new application oriented towards the chemical synthetic surfactant industry. Our present review gives comprehensive information on BS/BE which has been reported to be produced by marine microorganisms and their possible potential future applications.

Methods for investigating biosurfactants and bioemulsifiers: a review

Microorganisms produce biosurfactant (BS)/bioemulsifier (BE) with wide structural and functional diversity which consequently results in the adoption of different techniques to investigate these diverse amphiphilic molecules. This review aims to compile information on different microbial screening methods, surface active products extraction procedures, and analytical terminologies used in this field. Different methods for screening microbial culture broth or cell biomass for surface active compounds production are also presented and their possible advantages and disadvantages highlighted. In addition, the most common methods for purification, detection, and structure determination for a wide range of BS and BE are introduced. Simple techniques such as precipitation using acetone, ammonium sulphate, solvent extraction, ultrafiltration, ion exchange, dialysis, ultrafiltration, lyophilization, isoelectric focusing (IEF), and thin layer chromatography (TLC) are described. Other more elaborate techniques including high pressure liquid chromatography (HPLC), infra red (IR), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR), and fast atom bombardment mass spectroscopy (FAB-MS), protein digestion and amino acid sequencing are also elucidated. Various experimental strategies including static light scattering and hydrodynamic characterization for micelles have been discussed. A combination of various analytical methods are often essential in this area of research and a numbers of trials and errors to isolate, purify and characterize various surface active agents are required. This review introduces the various methodologies that are indispensable for studying biosurfactants and bioemulsifiers.

Concurrent synthetic control of dopant (nitrogen) and defect complexes to realize broadband (UV–650 nm) absorption in ZnO nanorods for superior photo-electrochemical performance

We report a facile solution based synthesis protocol to incorporate nitrogen within zinc oxide nanorods with substantially improved visible light harvesting via broadband absorption stretching from UV to deep visible wavelengths (650 nm). We also report a peculiar visible region maximum around 470 nm. Raman and X-ray photoelectron spectroscopy confirm incorporation of nitrogen along with other complex defects such as zinc interstitials and oxygen vacancies. Our N:ZnO appears pale orange as opposed to the pale yellow reported in other works. It exhibits significantly superior photo-electrochemical performance over undoped ZnO. Notably under monochromatic green light illumination (530 nm) N:ZnO shows a photocurrent density of 3.2 μA cm−2, whereas pristine ZnO fails to show any photo-response. The IPCE spectrum of N:ZnO follows the broadband absorption spectrum extending up to an unprecedented value of 650 nm, potentially expanding the scope for using our material in other solar energy harvesting applications.

Electrowetting --A versatile tool for controlling microdrop generation

Abstract.Integrating insulator-covered electrodes into a microfluidic flow focusing device (FFD) we demonstrate enhanced flexibility and control of the flow of two non-miscible liquids based on electrowetting (EW). In the parameters space, determined by liquid inlet pressures, we identify a specific region where drops can only be generated and addressed via EW. In this regime we show that the size distribution and the frequency of drop generation can be controlled by the applied voltage and the width of voltage pulses. Moreover it turns out that with EW the drop size and the frequency can be tuned independently. Finally we show that the same drop generation phenomena can also be observed in the presence of surfactants.

On the change in bacterial size and magnetosome features for Magnetospirillum magnetotacticum (MS-1) under high concentrations of zinc and nickel

The characteristic size, shape and specific alignment of magnetite crystals synthesized by magnetotactic bacteria is a highly coordinated process with precise control over magnetosome vesicle formation, uptake and transport of Fe, and magnetite biomineralization. Magnetosome membranes along with some specific membrane proteins regulate crystal nucleation and morphology of magnetite. Several previous works have indicated that the morphology of mature magnetite crystals is largely unaffected by environmental conditions, though some recent studies have shown the possibility of manipulation of the biomineralization process. In this study we have examined the effects of high concentrations of Zinc and Nickel on the growth of Magnetospirillum magnetotacticum (MS-1) and the corresponding magnetosome formation. Using various characterizations it is shown that the growth of the bacterial cells, as well as the size, shape and magnetosome chain alignment is significantly influenced in the presence of high concentrations of Zn or Ni.

High sensitivity low field magnetically gated resistive switching in CoFe2O4/La0.66Sr0.34MnO3 heterostructure

The phenomenon of resistive switching (RS) has been demonstrated in several non-magnetic and some magnetic oxide systems, however the “magnetic” aspect of magnetic oxides has not been emphasized especially in terms of low field tunability. In our work, we examined the CoFe2O4/La0.66Sr0.34MnO3 all-magnetic oxide interface system for RS and discovered a very sharp (bipolar) transition at room temperature that can be gated with high sensitivity by low magnetic fields (∼0–100 mT). By using a number of characterizations, we show that this is an interface effect, which may open up interesting directions for manipulation of the RS phenomenon.

Biosurfactant/s from Lactobacilli species: Properties, challenges and potential biomedical applications.

Lactic acid bacteria are generally believed to have positive roles in maintaining good health and immune system in humans. A number of Lactobacilli spp. are known to produce important metabolites, among which biosurfactants in particular have shown antimicrobial activity against several pathogens in the intestinal tract and female urogenital tract partly through interfering with biofilm formation and adhesion to the epithelial cells surfaces. Around 46 reports are documented on biosurfactant production from Lactobacillus spp. of which six can be broadly classified as cell free biosurfactant and 40 as cell associated biosurfactants and only approximately 50% of those have reported on the structural composition which, in order of occurrence were mainly proteinaceous, glycolipidic, glycoproteins, or glycolipopeptides in nature. Due to the proteinaceous nature, most biosurfactant produced by strains of Lactobacillus are generally believed to be surlactin type with high potential toward impeding pathogens adherence. Researchers have recently focused on the anti‐adhesive and antibiofilm properties of Lactobacilli‐derived biosurfactants. This review briefly discusses the significance of Lactobacilli‐derived biosurfactants and their potential applications in various fields. In addition, we highlight the exceptional prospects and challenges in fermentation economics of Lactobacillus spp.‐derived biosurfactants’ production processes.

Electrically tunable wetting defects characterized by a simple capillary force sensor.

We present a concept of a wetting defect of continuously variable strength based on electrowetting, along with a capillary force sensor adapted for the characterization of macroscopically heterogeneous surfaces. Patterned electrodes submerged under an insulating layer are used to generate potential wells for drops of electrically conductive liquids on the solid surface, with a well depth that scales with the diameter of the drop and square of the applied alternating (AC) voltage. We characterize the strength of the electrowetting trap and the hysteretic motion of the drop along the surface, using a simple force sensor based on optical imaging of a thin bendable capillary. A force resolution of approximately 0.1 μN is achieved.

CdTe–TiO2 nanocomposite: an impeder of bacterial growth and biofilm

The resurgence of infectious diseases and associated issues related to antibiotic resistance has raised enormous challenges which may possibly be confronted primarily by nanotechnology routes. One key need of critical significance in this context is the development of an agent capable of inhibiting quorum sensing mediated biofilm formation in pathogenic organisms. In this work we examine the possible use of a nanocomposite, CdTe-TiO2, as an impeder of growth and biofilm. In the presence of CdTe-TiO2, scanning electron microscopy (SEM) analysis shows exposed cells without the surrounding matrix. Confocal laser scanning microscopy shows spatially distributed fluorescence, a typical indication of an impeded biofilm, as opposed to the control which shows matrix-covered cells and continuous fluorescence, typical of biofilm formation. Quantitatively, the inhibition of biofilm was ∼57%. CdTe-TiO2 also exhibits good antibacterial properties against Gram positive and Gram negative organisms by virtue of the generation of reactive oxygen species inside the cells, reflected by a ruptured appearance in the SEM analysis.

A Quasi-Liquid Iontronic–Electronic Light-Harvesting Hybrid Photodetector with Giant Response

A heterostructure formed by a layer of agarose gel drop-cast on a hydrothermally grown layer of ZnO nanorods on fluorine-doped tin oxide (FTO)-coated glass is examined for photoresponse with a top platinum tip contact. This ionic-gel-based hybrid device shows three orders of magnitude higher photocurrent as compared to the case of bare ZnO nanorods film.