Pijus Kanti Samanta

ZnO nanoparticle-protein interaction: Corona formation with associated unfolding

The interaction as well as the formation of bioconjugate of Bovine Serum Albumin (BSA) and Zinc Oxide nanoparticles (ZnO NPs) is investigated. The surface binding along with reorganization of BSA on the surface of ZnO NPs forms stable “hard corona.” The time constants for surface binding and reorganization are found to be 1.10u2009min and 70.68u2009min, respectively. The close proximity binding of BSA with ZnO NPs via tryptophan is responsible for bioconjugate formation. Fibrillar aggregated structure of BSA is observed due to conformational change of BSA in interaction with ZnO NPs.

Biocompatibility study of protein capped and uncapped silver nanoparticles on human hemoglobin

The interactions of human hemoglobin with protein capped silver nanoparticles and bare silver nanoparticles were studied to understand fundamental perspectives about the biocompatibility of protein capped silver nanoparticles compared with bare silver nanoparticles. Bare silver (Ag) nanoparticles (NPs) were prepared by the chemical reduction method. High resolution transmission electron microscopy (HRTEM) analysis along with absorption at ~390 nm indicated the formation of bare Ag NPs. Protein coated Ag NPs were prepared by a green synthesis method. Absorption at ~440 nm along with ~280 nm indicated the formation of protein coated Ag NPs. The biocompatibility of the above mentioned Ag NPs was studied by interaction with human hemoglobin (Hb) protein. In presence of bare Ag NPs, the Soret band of Hb was red shifted. This revealed the distortion of iron from the heme pockets of Hb. Also, the fluorescence peak of Hb was quenched and red shifted which indicated that Hb became unfolded in the presence of bare Ag NPs. No red shift of the absorption of Soret, along with no shift and quenching of the fluorescence peak of Hb were observed in the presence of protein coated Ag NPs. A hemolysis assay suggested that protein coated Ag NPs were more biocompatible than bare one.

Safety concerns towards the biomedical application of PbS nanoparticles: An approach through protein-PbS interaction and corona formation

Semiconductor nanoparticles (NPs) with near-infrared (NIR) fluorescence has achieved great interest for early detection of colon tumors/cancer. We have synthesized lead sulphide (PbS) NPs (5–7 nm) having emission in NIR region and investigated its interaction with bovine serum albumin (BSA) to determine the bio-safety of PbS NPs. The interaction of PbS NPs with BSA occurs through formation of “hard” and “soft” protein NPs corona and follows exponential association. The hard corona represents that the core PbS NPs are fully covered by BSA with shell thickness of ∼8 nm, i.e., the dimension of BSA monomer. A large number of PbS NPs with hard corona of BSA forms “colony” with diameters in the range of 200–400 nm. The soft corona grows surrounding this colony. The quenching of fluorescence BSA in the presence of PbS NPs follows dynamic quenching process with tryptophan as major binding sites. Nearest to human body temperature, positive cooperative association between PbS NPs and BSA are found, and affinity of BSA to the PbS NPs gradually increases in superlinear fashion. The electrostatic interaction is the key force in binding of PbS NPs with BSA, and hydrophobic interaction between PbS NPs and BSA is responsible for conformational change of BSA.

Enhanced photoluminescence from ZnO/ZnS core-shell structure

The effect of ZnS coating over ZnO core is discussed in this present report. Very simple two step wet chemical method was used for the fabrication of this core-shell structure. XRD and HRTEM data reveal the formation of good shell coating over the ZnO core. Photoluminescence spectra shows that emission intensity is at least four times higher when coated with ZnS compare to bare ZnO. Band gap is also calculated usingxa0UV-vis spectroscopy. This study will be very useful towards tuning the emission properties and developing intense violet light-emitting and nanophotonic devices. n n xa0 n n Key words:xa0Core-shell, photoluminescence, violet emission, green emission.

Wet Chemically Synthesized CuO Bipods and their Optical Properties

BACKGROUNDnMetal oxide nanostructures are being investigated widely due to their strong optical absorption, efficient photoluminescence, abundant of availability and structural stability which lead them as a possible substitute of Si based solar cells and many optoelectronic and sensor devices. Due to their non-toxic nature they are supposed to be promising materials for drug delivery and medical research. Among several metal oxides, cupric oxide (CuO) is being investigated nowadays due to their high transparency and visible luminescence. It is a p-type semiconductor of band gap varying from 1.3 eV to 2.1 eV depending of the structure and process of fabrication. This low band gap of CuO nanostructures leads its application in photoconductive and photothermal applications. This leads rigorous investigations on CuO nanostructures.nnnMETHODSnA simple wet chemical methods has been used to synthesize CuO bipods. Predetermined amount of Copper sulphate penta-hydrate (CuSO4, 5H2O) was dissolved in double distilled de-ionized water to prepare 0.5 M solution. Predetermined amount of Lithium hydroxide (LiOH) was dissolved in de-ionized water to prepare 1 M solution. Under rigorous magnetic stirring of the LiOH solution CuSO4 solution was added drop by drop for five minutes and the stirring was maintained for 2 hours at room temperature (30°C). After the reaction a white precipitate was observed at the bottom of the flask. This solution was then aged for 24 hours. The color of the precipitate solution was turned into grey. The precipitate was filtered and subsequently washed with distilled de-ionized water thrice for the removal of unreacted salts if any. The precipitate was then dried in an ordinary furnace at 150°C for further characterization.nnnRESULTSnX-ray diffraction data confirmed the formation of well crystalline CuO having monoclinic unit cell structure. The crystallite size was ~ 12 nm as calculated from the XRD pattern. Transmission electron microscope images revealed that the bipod-like structure is composed of several crystallites. The lengths of the bipods are ~ 300 nm with a waist size ~ 100 nm. The UV-visible spectroscopic data revealed a strong absorption at ~ 376 nm and the band gap was calculated to be 2.51 eV. FTIR spectrum revealed the existence of only Cu=O bonds. In the Raman shift data two strong peaks were found at 273 cm-1, and 608 cm-1 that owe to the Ag mode and Bg mode respectively. Room temperature photoluminescence spectroscopy revealed that the CuO nanoparticles exhibit broad strong emission at ~ 472 nm. After decomposing we observed three peaks at 436, 469 and 495 nm. The emission peak at 469 nm arises due to near band edge transition. The emission peak at 495 nm arises due to shallow level defect states related transitions.nnnCONCLUSIONnIn conclusion, we have fabricated CuO nano-bipods using a simple wet chemical method. XRD pattern indicates the formation of well crystalline and pure CuO without any impurity. The nano-bipods exhibit sharp absorption peak at ~ 376 nm with optical band gap energy of 2.51 eV. FTIR spectrum and Raman shift data confirms the formation of CuO with the presence of Ag mode (273 cm-1) and Bg mode (608 cm-1). The fabricated CuO nano-bipods exhibit strong PL emission at 469 nm owing to the recombination of free excitons at the absorption band edge in the UV region associated with other low intense deep level emission. Few relevant patents to the topic have been reviewed and cited.