Ranu K. Dutta

Differential Susceptibility of Escherichia coli Cells toward Transition Metal-Doped and Matrix-Embedded ZnO Nanoparticles

Dependence of the antibacterial behavior on ZnO (TM-doped and surface-modified) nanoparticles on Escherichia coli cells has been investigated. ZnO nanoparticles that differ in size, activator ion and in the microenvironment in which these nanoparticles are embedded were used. Comprehensive antibacterial studies of these ZnO nanoparticles owing to their size and surface defects are carried out against E. coli cells. These studies have been carried out both in Luria-Bertani medium and on solid agar medium in the presence and absence of light. The differences in antibacterial effect have been quantified in terms of minimum inhibitory concentration, minimum bactericidal concentration, colony forming unit counts, and qualitatively evaluated by growth curves and disk diffusion tests. The difference in antibacterial activities of the ZnO nanoparticles may be attributed to the enhanced or reduced oxygen vacancies and defect states and could be attributed to the increased or decreased surface defects.

Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles

Single-phase ZnO:Co(2+) nanoparticles of mean size 2-8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co(2+) ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co(2+), the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co-Co ions suppressed the ferromagnetism at higher doping concentrations of Co(2+). Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies.

Size dependence of Eu-O charge transfer process on luminescence characteristics of YBO3:Eu3+ nanocrystals

Well-crystallized pure hexagonal phase YBO(3):Eu(3+) nanoparticles are prepared by the reverse micelles method. Vacuum ultraviolet photoluminescence (VUVPL) spectroscopy showed size-dependent nonlinear luminescence enhancement with remarkably improved chromaticity (0.62, 0.34), as compared to the commercial bulk YBO(3):Eu(3+) phosphor (0.56, 0.39). The quenching concentration of Eu(3+) doping and the ratio of red ((5)D(0)-->(7)F(2)) to orange ((5)D(0)-->(7)F(1)) emission was found significantly enhanced with the decrease in particle size, making it an ideal VUV phosphor for plasma display panels. The possible explanation for size dependence of the Eu-O charge transfer process via lowering of the structural symmetry is proposed in detail.

Doping, strain, defects and magneto-optical properties of Zn1−xMnxO nanocrystals

This paper presents the co-relation between doping induced defects, structural, magnetic and optical properties of chemically grown Mn doped ZnO nanocrystals. The solubility limit of Mn in ZnO is found to be ∼10%. X-ray diffraction (XRD), Raman spectroscopy and high resolution transmission electron microscope (HRTEM) are employed to study the doping induced defects. These studies confirm that undoped and Mn doped (up to 10%) nanoparticles have lesser defects as compared to 15–20% Mn doped nanocrystals. Noticeable increases in strain with a significant decrease in lattice parameters and bond length were observed for nanocrystals doped with 10% or higher Mn concentrations. In contrast to previous observations of room temperature ferromagnetism in undoped ZnO nanoparticles, we observe diamagnetic behavior of the sample due to lesser oxygen vacancies in these samples. Doped samples show room temperature ferromagnetism and as Mn concentration increases, saturation magnetization decreases due to enhanced anti-ferromagnetic interaction between Mn–Mn ions. Luminescence studies show a significantly visible change in the emission (bright blue → bright green) characteristics with increasing dopant concentration. Currently, LEDs giving UV emission have been combined with broadband visible green phosphors to make white-light LEDs. Thus observed magnetic and optical properties could be utilized in different opto-electronic, dilute magnetic semiconductors (DMS)/spintronics and bio-imaging applications, underlying the findings and importance of current investigations.

Red luminescent manganese-doped zinc sulphide nanocrystals and their antibacterial study

Water soluble, uniform-sized ZnS:Mn2+ nanocrystals (NCs) have been prepared using a simple co-precipitation method with a methanol and water binary mixture as a reaction medium. The structure of the prepared ZnS:Mn2+ NCs is cubic with a mean size distribution of 3-5 nm. Photoluminescence (PL) studies showed emission at ∼612 nm, which is 22 nm red shifted as compared with the reported literature. This red shift could be attributed to the observed distortion in the imaged lattice plane. The capping effect of pepsin, citric acid and biotin on the optical properties of ZnS:Mn2+ NCs has been examined and the maximum enhancement in PL Intensity was found in the case of biotin. The synthesised ZnS:Mn2+ NCs were characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) for investigation of their structural properties. Because of the high PL intensity, biotin capped ZnS:Mn2+ NCs were further investigated for their anti-bacterial activity against gram negative and gram positive bacteria. These NCs show broad spectrum antibacterial activity against both types of bacteria having an MIC value of 100 ng ml-1 for B. subtilis.

Highly Stabilized Monodispersed Citric Acid Capped

Nanophosphors of ZnO:Cu2+ were synthesized by a chemical technique based on coprecipitation method. The synthesized nanophosphors were annealed at different temperatures (100-400°C) in steps of 100°C for 4 h. A reduction in photoluminescence intensity was observed with increase in the annealing temperature. Further, these nanophosphors were capped with citric acid, which results in enhancement in the luminescence intensity. These surface-modified ZnO nanoparticles were found to be remarkably stable. The reduction in luminescence with annealing temperature occurred due to removal of surface defects and intrinsic impurities, while the citric acid reduced the unsaturated bond density and passivated the surface, resulting in reduction in the number of surface trap sites for nonradiative recombination processes to occur, enhancing the luminescence intensity. Currently, LEDs giving UV emission have been combined with broadband visible green phosphors to make white-light LEDs. Thus, green luminescent ZnO:Cu2+ nanoparticles can be seen as necessary and critical constituent for white light generation from UV LEDs, underlying the findings and importance of current investigations. Besides this citric acid capped ZnO:Cu2+ nanophosphors can also be used in biological (drug delivery system, bioimaging, etc.) and biosensors.

\hbox{ZnO:Cu}^{2+}

The present letter deals with the synthesis of ultrasmall Gd2S3:Eu3+ nanoparticles and their surface modification with “cytosine,” a nucleobase present in DNA/RNA. These nanoparticles show orthorhombic (Pnma) crystal symmetry with excellent magnetic and luminescent characters simultaneously. In contrast to the previous reports, cytosine modified nanoparticles do not show a significant change in their structural and magnetic properties, whereas luminescence is enhanced slightly owing to the surface passivation. The in vitro studies show better accumulation of blood platelets with cytosine modified nanoparticles as compared to unmodified posing them a potential candidate for platelet isolation from the plasma for different applications and studies.

Nanoparticles: Synthesis and Characterization for Their Applications in White Light Generation From UV LEDs

The luminous efficiency and lifetime of plasma display panels (PDPs) are directly related to the performance of phosphors used in PDPs, thus higher efficiency, higher stability against high temperature processes, and a long lifetime along with good color chromaticity against vacuum-ultraviolet radiation are major concerns in selecting suitable phosphors for PDPs. In the same pursuit, well crystallized pure hexagonal phase YBO3:Tb3+ nanocrystals were prepared using co-precipitation method. The prepared YBO3:Tb3+ nanocrystals showed bright green luminescence, color chromaticity (0.21, 0.61), and could be assigned to 5D4→7Fj transitions (j = 2-6) due to electric dipole–dipole interaction of Tb3+ ions. The vacuum ultraviolet photoluminescence spectroscopy of the prepared YBO3:Tb3+ nanocrystals showed size dependent nonlinear luminescence enhancement with relatively shorter life time as compared to the commercial bulk YBO3:Tb3+ phosphor. The quenching concentration of Tb3+ doping for (5D4→7F5) transition was f...

DNA base (cytosine) modified/capped ultrasmall Gd2S3:Eu3+ gadofluoroprobes for platelet isolation

Gadolinium chelates and gadolinium based inorganic nanoparticles have been extensively studied, because of the high magnetic moment of gadolinium. Here, metallic gadolinium nanocongregates have been developed. Upon injecting these nanoparticles in the mice, they initially circulate in the blood stream and are localized at the cancer site, which could be visualized upon application of magnetic field hence acting as small magnetic nanosensors searching for even small cancers, detecting cancers at a very early stage.

Size-dependent emission efficiency and luminescence characteristics of YBO3:Tb3+ nanocrystals under vacuum ultraviolet excitations

The spherical nanophosphors of ZnO of mean size 10–20 nm were synthesized at room temperature by simple co‐precipitation method. Their size and shape were governed by several encapsulations using compounds like biotin, citric acid and Poly vinyl alcohol (PVA). Besides playing a critical role in determining their size and shape, these biomolecules served as effective capping agents. The antibacterial behavior of the suspension of fine ZnO nanophosphors was investigated against the gram negative bacillus Escherichia coli. The growth curve showed bacteriostatic activity against Escherichia coli. The antibacterial activities of the ZnO nanophosphors can be attributed to their total surface area, as increasing surface to volume ratio of nanophosphors provides more efficient means for enhanced antibacterial activity.