Sub-70†nm surface structures on femtosecond laser irradiated GaAs in distilled water and sensing application.

This study reveals the possibility of distinct ablation mechanisms at different radial positions of the ablated track on GaAs when ablated with femtosecond pulses in distilled water. From the center to the edges of the ablated track, fascinating features such as micron-sized cones, nano-pores, and nano-ripple trenches (average size of 60-70 nm) were observed. The requirement for simulations incorporating the variations in a Gaussian beam fluence and dynamics of the melt flow/surrounding media is discussed. Deep-subwavelength structures, i.e., nano-ripple trenches with a ripple size of ∼λ/11 are achieved on the GaAs surface in this study. Further, these GaAs surface structures acted as excellent hybrid surface-enhanced Raman spectroscopy platforms upon gold coating.

Trace level detection of explosives and pesticides using robust, low-cost, free-standing silver nanoparticles decorated porous silicon.

We report results from our extensive studies on the fabrication of ultra-thin, flexible, and cost-effective Ag nanoparticle (NP) coated free-standing porous silicon (FS-pSi) for superior molecular sensing. The FS-pSi has been prepared by adopting a simple wet-etching method. The deposition time of AgNO3 has been increased to improve the number of hot-spot regions, thereby the sensing abilities are improved efficiently. FESEM images illustrated the morphology of uniformly distributed AgNPs on the pSi surface. Initially, a dye molecule [methylene blue (MB)] was used as a probe to evaluate the sensing capabilities of the substrate using the surface-enhanced Raman scattering (SERS) technique. The detection was later extended towards the sensing of two important explosive molecules [ammonium nitrate (AN), picric acid (PA)], and a pesticide molecule (thiram) clearly demonstrating the versatility of the investigated substrates. The sensitivity was confirmed by estimating the analytical enhancement factor (AEF), which was ∼107 for MB and ∼104 for explosives and pesticides. We have also evaluated the limit of detection (LOD) values in each case, which were found to be 50 nM, 1 µM, 2 µM, and 1 µM, respectively, for MB, PA, AN, and thiram. Undeniably, our detailed SERS results established excellent reproducibility with a low RSD (relative standard deviation). Furthermore, we also demonstrate the reasonable stability of AgNPs decorated pSi by inspecting and studying their SERS performance over a period of 90 days. The overall cost of these substrates is attractive for practical applications on account of the above-mentioned superior qualities.

Femtosecond Laser-Induced, Nanoparticle-Embedded Periodic Surface Structures on Crystalline Silicon for Reproducible and Multi-utility SERS Platforms.

Fabrication of reproducible and versatile surface-enhanced Raman scattering (SERS) substrates is crucial for real-time applications such as explosive detection for human safety and biological imaging for cancer diagnosis. However, it still remains a challenging task, even after several methodologies were developed by various research groups, primarily due to (a) a lack of consistency in detection of a variety of molecules (b) cost-effectiveness of the SERS substrates prepared, and (c) byzantine preparation procedures, etc. Herein, we establish a procedure for preparing reproducible SERS-active substrates comprised of laser-induced nanoparticle-embedded periodic surface structures (LINEPSS) and metallization of silicon (Si) LINEPSS. LINEPSS were fabricated using the technique of femtosecond laser ablation of Si in acetone. The versatile SERS-active substrates were then achieved by two ways, including the drop casting of silver (Ag)/gold (Au) nanoparticles (NPs) on Si LINEPSS and Ag plating on the Si LINEPSS structures. By controlling the LINEPSS grating periodicity, the effect of plasmonic nanoparticles/plasmonic plating on the Si NPs embedded periodic surface structures enormously improved the SPR strength, resulting in the consistent and superior Raman enhancements. The reproducible SERS signals were achieved by detecting the molecules of Methylene Blue (MB), 2,4-dinitrotoluene (DNT), and 5-amino-3-nitro-l,2,4-triazole (ANTA). The SERS signal strength is determined by the grating periodicity, which, in turn, is determined by the input laser fluence. The SERS-active platform with grating periodicity of 130 ± 10 nm and 150 ± 5 nm exhibited strong Raman enhancements of ∼108 for MB and ∼107 for ANTA molecules, respectively, and these platforms are demonstrated to be capable, even for multiple usages.

Molecular identification of arsenic-resistant estuarine bacteria and characterization of their ars genotype.

In the present study, 44 arsenic-resistant bacteria were isolated through serial dilutions on agar plate with concentrations ≥0.05 mM of sodium arsenite and ≥10 mM of sodium arsenate from Mandovi and Zuari--estuarine water systems. The ars genotype characterization in 36 bacterial isolates (resistant to 100 mM of sodium arsenate) revealed that only 17 isolates harboured the arsA (ATPase), B (arsenite permease) and C (arsenate reductase) genes on the plasmid DNA. The arsA, B and C genes were individually detected using PCR in 16, 9 and 13 bacterial isolates respectively. Molecular identification of the 17 isolates bearing the ars genotype was carried using 16S rDNA sequencing. A 1300 bp full length arsB gene encoding arsenite efflux pump and a 409 bp fragment of arsC gene coding for arsenate reductase were isolated from the genera Halomonas and Acinetobacter. Phylogenetic analysis of arsB and arsC genes indicated their close genetic relationship with plasmid borne ars genes of E. coli and arsenate reductase of plant origin. The putative arsenate reductase gene isolated from Acinetobacter species complemented arsenate resistance in E. coli WC3110 and JM109 validating its function. This study dealing with isolation of native arsenic-resistant bacteria and characterization of their ars genes might be useful to develop efficient arsenic detoxification strategies for arsenic contaminated aquifers.

Bacterial diversity and bioprospecting for cold-active lipases, amylases and proteases, from culturable bacteria of kongsfjorden and Ny-alesund, Svalbard, Arctic.

Culturable bacterial diversity of seven marine sediment samples of Kongsfjorden and a sediment and a soil sample from Ny-Alesund, Svalbard, Arctic was studied. The bacterial abundance in the marine sediments of Kongsfjorden varied marginally (0.5 x 10(3)-1.3 x 10(4) cfu/g sediment) and the bacterial number in the two samples collected from the shore of Ny-Alesund also was very similar (0.6 x 10(4) and 3.4 x 10(4), respectively). From the nine samples a total of 103 bacterial isolates were obtained and these isolates could be grouped in to 47 phylotypes based on the 16S rRNA gene sequence belonging to 4 phyla namely Actinobacteria, Bacilli, Bacteroidetes and Proteobacteria. Representatives of the 47 phylotypes varied in their growth temperature range (4-37 degrees C), in their tolerance to NaCl (0.3-2 M NaCl) and growth pH range (2-11). Representatives of 26 phylotypes exhibited amylase and lipase activity either at 5 or 20 degrees C or at both the temperatures. A few of the representatives exhibited amylase and/or lipase activity only at 5 degrees C. None of the phylotypes exhibited protease activity. Most of the phylotypes (38) were pigmented. Fatty acid profile studies indicated that short chain fatty acids, unsaturated fatty acids, branched fatty acids, the cyclic and the cis fatty acids are predominant in the psychrophilic bacteria.

Increased vincristine production from Agrobacterium tumefaciens C58 induced shooty teratomas of Catharanthus roseus G. Don.

Dimeric indole alkaloids are used extensively for cancer therapy. Agrobacterium tumefaciens C58 strain was used for induction of shooty teratoma in Catharanthus roseus using epicotyl and stem node explants. The transformed nature of shooty teratomas was confirmed by nopaline assay. Growth kinetics of shooty teratomas depicted maximum growth during 21-24 days of culture. Dimeric alkaloid vincristine in the transformed cultures was present at a concentration of 0.011 that was tenfold higher compared to untransformed control cultures.

Vibrational lifetimes and frequency-gap law of hydrogen bending modes in semiconductors.

Vibrational lifetimes of hydrogen and deuterium related bending modes in semiconductors are measured by transient bleaching spectroscopy and high-resolution infrared absorption spectroscopy. We find that the vibrational lifetimes follow a universal frequency-gap law; i.e., the decay time increases exponentially with increasing decay order, with values ranging from 1 ps for a one-phonon process to 265 ps for a four-phonon process. The temperature dependence of the lifetime shows that the bending mode decays by lowest-order multiphonon process. Our results provide new insights into vibrational decay and the giant isotope effect of hydrogen in semiconductor systems.

Phylogenetic relationships of three new microsporidian isolates from the silkworm, Bombyx mori.

The pathogenicity, mode of transmission, tissue specificity of infection and the small subunit rRNA (SSU-rRNA) gene sequences of the three new microsporidian isolates from the silkworm Bombyx mori were studied. Out of the three, NIK-2r revealed life cycle features and SSU-rRNA gene sequence similar to Nosema bombycis, suggesting that it is N. bombycis. The other two, NIK-4m and NIK-3h, differed from each other as well as from N. bombycis. NIK-4m was highly pathogenic and did not show any vertical transmission, in accordance with the apparent lack of gonadal infection, whereas NIK-3h was less pathogenic and vertical transmission was not detected but could not be excluded. Phylogenetic analysis based on SSU-rRNA gene sequence placed NIK-3h and NIK-4m in a distinct clade that included almost all the Vairimorpha species and Nosema species that infect lepidopteran and non-lepidopteran hosts, while NIK-2r was included in a clade containing almost all the Nosema isolates that infect only lepidopteran hosts. Thus, we have presented molecular evidence that one of the three isolates is in fact the type species N. bombycis, while the other two isolates are Vairimorpha spp. There was distinct separation of microsporidian isolates infecting only lepidopteran hosts and those infecting lepidopteran and non-lepidopteran hosts, reflecting possible co-evolution of hosts and microsporidian isolates.