Virendra Shanker

Contrasting Effect of Gold Nanoparticles and Nanorods with Different Surface Modifications on the Structure and Activity of Bovine Serum Albumin

Nanoparticles exposed to biofluids become coated with proteins, thus making protein-nanoparticle interactions of particular interest. The consequence on protein conformation and activity depends upon the extent of protein adsorption on the nanoparticle surface. We report the interaction of bovine serum albumin (BSA) with gold nanostructures, particularly gold nanoparticles (GNP) and gold nanorods (GNR). The difference in the geometry and surface properties of nanoparticles is manifested during complexation in terms of different binding modes, structural changes, thermodynamic parameters, and the activity of proteins. BSA is found to retain native-like structure and properties upon enthalpy-driven BSA-GNP complexation. On the contrary, the entropically favored BSA-GNR complexation leads to substantial loss in protein secondary and tertiary structures with the release of a large amount of bound water, as indicated by isothermal calorimetry (ITC), circular dichroism (CD), and Fourier transform infrared (FTIR) and fluorescence spectroscopies. The esterase activity assay demonstrated a greater loss in BSA activity after complexation with GNR, whereas the original activity is retained in the presence of GNP. The formation of large assemblies (aggregates) and reduced average lifetime, as evidenced from dynamic light scattering and fluorescence decay measurements, respectively, suggest that GNR induces protein unfolding at its surface. The effect of temperature on the CD spectra of BSA-GNP was found to be similar to that of pristine BSA, whereas BSA-GNR shows distortion in CD spectra at lower wavelengths, strengthening the perception of protein unfolding. High binding constant and entropy change for BSA-GNR complexation determined by ITC are consistent with large surfacial interaction that may lead to protein unfolding. The present work highlights the differential response of a protein depending on the nature of the nanostructure and its surface chemistry, which need to be modulated for controlling the biological responses of nanostructures for their potential biomedical applications.

Synthesis and characterization of ultra-fine Y2O3:Eu3+ nanophosphors for luminescent security ink applications

We report a simple method for the synthesis of ultra-fine Eu(3+)-doped yttria (Y(2)O(3)) nanophosphors with an average diameter of approximately 5 nm for development of a transparent colloid that could be used as a luminescent security ink. This has been achieved by suitably substituting Eu(3+) ions at the favorable C(2) symmetry sites of Y(3+) ions and quantum mechanically confining the growth of the nanophosphor using a novel acid-catalyzed sol-gel technique. This is one of the few reports that depict the development of a transparent aqueous-stable Y(2)O(3):Eu(3+) colloidal solution for strategic applications related to security codes. High resolution transmission electron microscopy images showed excellent lattice fringes that in turn support the presence of better crystal quality and enhanced photoluminescence (PL) emission from the Y(1.9)O(3)Eu(0.1)(3+) nanophosphor system. Time resolved emission spectroscopy measurement indicated a PL decay time in the range of a few milliseconds, suitable for making luminescent security ink and other advanced applications in optoelectronic devices and bio-labeling.

Interaction of Polyethyleneimine-Functionalized ZnO Nanoparticles with Bovine Serum Albumin

In biological fluids, nanoparticles are always surrounded by proteins. As the protein is adsorbed on the surface, the extent of adsorption and the effect on the protein conformation and stability are dependent on the chemical nature, shape, and size of the nanoparticle (NP). We have carried out a detailed investigation on the interaction of bovine serum albumin (BSA) with polyethyleneimine-functionalized ZnO nanoparticles (ZnO-PEI). ZnO-PEI was synthesized using a wet chemical method with a core size of ~3-7 nm (from transmission electron microscopy). The interaction of BSA with ZnO-PEI was examined using a combination of calorimetric, spectroscopic, and computational techniques. The binding was studied by ITC (isothermal titration calorimetry), and the result revealed that the complexation is enthalpy-driven, indicating the possible involvement of electrostatic interaction. To investigate the nature of the interaction and the location of the binding site, a detailed domain-wise surface electrostatic potential calculation was performed using adaptive Poisson-Boltzmann software (APBS). The result shows that the protein surface can bind the nanoparticle. On binding ZnO-PEI, the protein gets destabilized to some extent, as displayed by CD (circular dichroism) and FTIR (Fourier transform infrared) spectroscopy. Chemical and thermal denaturation of BSA, when carried out in the presence of ZnO-PEI, also indicated a small perturbation in the protein structure. A comparison of the enthalpy and entropy components of binding with those derived for the interaction of BSA with ZnO nanoparticles explains the effect of hydrophilic cationic species attached on the NP surface. The effect of the NP surface modification on the structure and stability of BSA would find useful applications in nanobiotechnology.

Binding of chloroquine–conjugated gold nanoparticles with bovine serum albumin

We have conjugated chloroquine, an anti-malarial, antiviral and anti-tumor drug, with thiol-functionalized gold nanoparticles and studied their binding interaction with bovine serum albumin (BSA) protein. Gold nanoparticles have been synthesized using sodium borohydride as reducing agent and 11-mercaptoundecanoic acid as thiol functionalizing ligand in aqueous medium. The formation of gold nanoparticles was confirmed from the characteristic surface plasmon absorption band at 522 nm and transmission electron microscopy revealed the average particle size to be ~7 nm. Chloroquine was conjugated to thiolated gold nanoparticles by using EDC/NHS chemistry and the binding was analyzed using optical density measurement and Fourier transform infrared spectroscopy. The chloroquine-conjugated gold nanoparticles (GNP-Chl) were found to interact efficiently with BSA. Thermodynamic parameters suggest that the binding is driven by both enthalpy and entropy, accompanied with only a minor alteration in proteins structure. Competitive drug binding assay revealed that the GNP-Chl bind at warfarin binding site I in subdomain IIA of BSA and was further supported by Trp212 fluorescence quenching measurements. Unraveling the nature of interactions of GNP-Chl with BSA would pave the way for the design of nanotherapeutic agents with improved functionality, enriching the field of nanomedicine.

Highly luminescent-paramagnetic nanophosphor probes for in vitro high-contrast imaging of human breast cancer cells.

Highly luminescent-paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high-quality, ultrafine, europium-doped yttrium oxide nanophosphors (Y(1.9)O(3):Eu(0.1)(3+)) using a modified sol-gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high-contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu(3+) peaking at 610 nm ((5)D(0)-(7)F(2)) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time-resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.

The anticancer activity of chloroquine-gold nanoparticles against MCF-7 breast cancer cells.

In the present study, 11-mercaptoundecanoic acid-modified gold nanoparticles (∼7 nm) were conjugated with chloroquine to explore their potential application in cancer therapeutics. The anticancer activity of chloroquine-gold nanoparticle conjugates (GNP-Chl) was demonstrated in MCF-7 breast cancer cells. The MCF-7 cells were treated with different concentrations of GNP-Chl conjugates, and the cell viability was assayed using trypan blue, resulting in an IC(50) value of 30 ± 5 μg/mL. Flow cytometry analysis revealed that the major pathway of cell death was necrosis, which was mediated by autophagy. The drug release kinetics of GNP-Chl conjugates revealed the release of chloroquine at an acidic pH, which was quantitatively estimated using optical absorbance spectroscopy. The nature of stimuli-responsive drug release and the inhibition of cancer cell growth by GNP-Chl conjugates could pave the way for the design of combinatorial therapeutic agents, particularly nanomedicine, for the treatment of cancer.

Probing a Bifunctional Luminomagnetic Nanophosphor for Biological Applications: a Photoluminescence and Time‐Resolved Spectroscopic Study

and core–shell nanocomposites. [ 4 ] All of these materials are either composites or hybrid structures combining luminescent and magnetic materials individually. In these materials, organic dyes or metal complexes were immobilized on a silica layer, which leads to critical problems of leaching and photobleaching. [ 4a ] Alternatively, semiconductor quantum dots such as CdS, CdSe, and CdTe, have been demonstrated to be highly effective for cellular and animal imaging. [ 5 ] However, the use of such colloids for bioimaging applications suffers from additional issues such as toxicity, harmful solvents, and additives, [ 6 ] low light penetration depth, surface-ligand

Intense red-emitting Y4Al2O9:Eu3+ phosphor with short decay time and high color purity for advanced plasma display panel.

A new phosphor Y(4)Al(2)O(9):Eu(3+) (YAM:Eu(3+)) emitting intense monochromatic red at 612 nm under vacuum ultraviolet (VUV) and ultraviolet (UV) excitations has been developed for application in next generation plasma display panels (PDPs). The developed phosphor has better luminescence efficiency, colour purity and shorter decay time than commercial (Y,Gd)BO(3):Eu(3+) red emitting PDP phosphor. High color purity (x = 0.67, y = 0.32) under VUV excitation with short decay time (1.03 msec) and excellent stability against degradation during PDP panel preparation suggest that YAM:Eu(3+) is a potential candidate for present and future PDPs. Surface coating by SiO(2) further improved phosphor characteristics.

A commercial approach for the fabrication of bulk and nano phosphors converted into highly efficient white LEDs

Herein, we report a strategy to synthesize a highly efficient yellow light emitting Y3−xAl5O12:Cex (x = 0.03 to 0.3) based bulk as well as nano (rod-shaped) phosphors, which are the main component of solid state white light-emitting diodes (WLEDs). The as-synthesized phosphors were well characterized by several experimental techniques related to material characterization and spectroscopy. The bulk and nano phosphors emit with maximum photoluminescence intensities at 549 and 530 nm, respectively, upon excitation at a wavelength of 468 nm. These phosphors exhibit higher photoluminescence intensity as compared to commercially available bulk phosphors coated on WLED strips. Moreover, the integration of commercially available InGaN blue LED strips with the synthesized bulk and nano phosphors demonstrates better CIE coordinates and lower colour temperature with high brightness (>81% quantum yield) compared to commercially available WLED-based strips, lanterns and torches. These highly efficient light-emitting phosphors are a feasible candidate for potential use in commercial WLED applications.

Tuning of emission colours in strontium aluminate long persisting phosphor

Solid-state preparation, structure, and multi-colour luminescence of Eu2+ doped strontium aluminate (SRA) phosphors have been reported in this paper. It has been observed that a slight modification in the processing parameters such as type of reducing atmosphere, stoichiometric excess of one or more constituents, nature of fluxes, and intentional addition of carbon or rare-earth halides can drastically shift the emission colours of the SRA phosphor in the visible spectrum. X-ray diffraction analysis and scanning electron microscopy observations of the samples revealed the formation of different crystalline phases related to the SRA system. The luminescence measurements showed that the decay times varied with the emission colours of the samples.