S. N. Sahu

In vitro biosynthesis and genotoxicity bioassay of silver nanoparticles using plants

Silver nanoparticles (AgNP-P) from AgNO(3) were synthesized by using the broth prepared from the aromatic spath of male inflorescence of screw pine, Pandanus odorifer (Forssk.) Kuntze AgNP-P was then characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Functional groups in the broth were analyzed by Fourier Transform infrared spectroscopy (FTIR). Genotoxicity of AgNP-P was assessed by utilizing our well-established Allium cepa assay system with biomarkers including the generation reactive oxygen species (ROS: O(2)(·-) and H(2)O(2)), cell death, mitotic index, micronucleus, mitotic aberrations; and DNA damage by Comet assay. Other chemical forms of silver such as Ag(+) ion, colloidal AgCl, and AgNP-S at doses 0-80 mg L(-1) were included for comparison with AgNP-P. The results revealed that AgNP-P and AgNP-S exhibited similar biological effects in causing lesser extent of cytotoxicity and greater extent of genotoxicity than that was exhibited by Ag(+) ion alone. Among different tested chemical forms of silver, colloidal AgCl was identified to be the least cytotoxic and genotoxic. Cell death and DNA-damage induced by AgNP-P were prevented by Tiron and dimethyl thiourea that scavenge O(2)(·-) and H(2)O(2), respectively. The present findings demonstrated the role of ROS in the AgNP-induced cell death and DNA damage.

Optical properties of CdS nanocrystalline films prepared by a precipitation technique

Abstract CdS semiconductor films of different crystalline size have been grown by a precipitation technique. The crystalline sizes were controlled by the reaction time period, pH/temperature of the solution and thickness of the deposit. From the optical absorption, the band gap of bulk-CdS is found to be 2.405 eV and is increased to 2.97 eV for nanocrystalline samples of average crystalline size 5.0 nm estimated from the blue shift. AFM analysis were performed to estimate the average crystalline size. Photoluminescence studies of CdS nanocrystalline samples show a red shift. The intensity of red luminescence (∼1.8 eV) decreases and its peak position shifts to the lower energy upon increasing the particle size. Photovoltage as a function of crystalline size/band gap has been studied using a photoelectrochemical solar cell configuration Ti/CdS/S2−, S22−/Pt.

Au-nanocluster emission based glucose sensing

Fabrication of a glucose biosensor based on Au-cluster emission quenching in the UV region is reported. The glucose biosensor is highly sensitive to β-d-glucose in 2.5-25.0mM range as confirmed from a linear calibration plot between Au-cluster colloid emission intensity as a function of β-d-glucose concentration. The interaction of β-d-glucose with l-cysteine capped Au cluster colloids has been confirmed from their Fourier transformed infrared spectroscopy (FTIR) measurements. It has been found that the biomolecules present in the serum such as ascorbic and uric acids, proteins and peptides do not interfere and affect in glucose estimation as confirmed from their absorption and fluorescence (FL) emission measurements. Practical utility of this sensor based on FL quenching method has been demonstrated by estimating the glucose level in human serum that includes diabetes and the data were found to be comparable or more accurate than those of the pathological data obtained from a local hospital. In addition, this biosensor is useful to detect glucose level over a wide range with sensor response time of the order of nano to picoseconds that is emission lifetime of Au clusters.

Self-assembled heterojunction between electrodeposited PbS nanoparticles and indium tin oxide substrate

Self-assembled heterojunction was fabricated by means of an electrochemical deposition of PbS nanoparticles on indium tin oxide substrate. The current–voltage and capacitance–voltage studies confirmed the formation of a heterojunction. A large current and large capacitance were observed in the case of a device from particle of smaller size which is believed to be due to the large surface area contact. The rectifying behavior of the heterojunction was found to be weak as compared to the usual p–n junction.

Strong UV absorption and emission from L-cysteine capped monodispersed gold nanoparticles

We report a synthesis of L-cysteine capped monodispersed gold (Au) nanoparticles (NPs) with size ∼2.0 nm exhibiting a strong surface plasmon resonance optical absorption at 3.13 eV, which is blueshifted by 1.01 eV compared to the uncapped Au NPs of size 20.0 nm. A strong fluorescence (FL) of the capped Au NPs appears at 3.25 eV, whereas the uncapped Au NPs do not show any FL in this range. The L-cysteine concentration has been optimized to achieve one of the strongest ultraviolet absorption and luminescence. The capping of Au NPs has been confirmed by Fourier transform infra red measurement.

Measurement of surface roughness by atomic force microscopy and Rutherford backscattering spectrometry of CdS nanocrystalline films

Surface roughness of chemically prepared CdS samples of different thicknesses were studied by atomic force microscopy and Rutherford backscattering spectrometry. Both the studies qualitatively gave the same roughness and were found to increase with increasing thickness.

INTERFACE CHARACTERIZATION OF NANOCRYSTALLINE CDS/AU JUNCTION BY CURRENT-VOLTAGE AND CAPACITANCE-VOLTAGE STUDIES

A Schottky junction in the configuration ITO/nano-CdS/Au has been fabricated and the current(I)–voltage(V) and capacitance(C)–voltage(V) characteristics studied. The I–V studies show series resistance effect resulting in two ideality factors: one in low and the other in high forward bias regime, suggesting the presence of surface/interface traps in nano-CdS. Frequency dependent capacitance has also been studied and different semiconductor parameters have been estimated from the I–V and C–V analysis.

The lattice contraction of nanometre-sized Sn and Bi particles produced by an electrohydrodynamic technique

The size dependence of lattice contraction can be understood by assuming the nanoparticles to be a liquid drop and that there exists a pressure difference (?p) between the inside and outside of the liquid drop. The analysis of the experimental data of Yu et al on the lattice contraction reveals that the isothermal compressibility is different for different orientations of the lattice plane, which is in good agreement with earlier reported data.

Visible light emission from CdS nanocrystals

Room temperature green and red light emission under ultra violet radiation have been observed from CdS nanocrystals. The chemical route used suggested a size distribution of nanocrystallites and was confirmed by atomic force microscopy analysis. The red band photoluminescence is ascribed to the presence of CdO phase as donor in CdS.

CdS Nanocrystalline films: Composition, surface, crystalline size, structural and optical absorption studies

Abstract Thin films of CdS nanopartides of different crystalline sizes have been grown by a precipitation technique and characterized by PIXE, RBS, AFM, SEM. XRD and optical absorption studies. PIXE studies identify the presence of Cd and S and indicate the absence of any foreign impurity even at ppm level, whereas RBS analysis identifies excess Cd in nano-CdS deposit. The bulk-CdS gave stoichiometric CdS film. XRD analysis show presence of mixed cubic and hexagonal phases for bulk CdS films, whereas for nano-CdS samples predominantly a cubic phase have been identified. AFM and SEM analysis show a rough and spongy morphology for all the samples which increases with increasing crystalline size/thickness. From AFM and optical absorption studies, the geometry of the nanopartides is predicted to be non-spherical.