Namdeo S. Gajbhiye

Induction heating studies of Fe3O4 magnetic nanoparticles capped with oleic acid and polyethylene glycol for hyperthermia

Fe3O4 magnetic nanoparticles (Fe3O4-MN) capped with either oleic acid (Fe3O4-OA-MN) or polyethylene glycol (Fe3O4-PEG-MN) were prepared by a co-precipitation method. From X-ray diffraction studies, the average crystallite sizes of Fe3O4-MN, Fe3O4-OA-MN and Fe3O4-PEG-MN were found to be 12, 6 and 8 nm, respectively. A reduction in the agglomeration of particles was observed when the magnetic nanoparticles (MN) were capped with oleic acid (OA) and polyethylene glycol (PEG), as confirmed by a transmission electron microscopy study. Magnetization of these MN was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Magnetization was lower and the superparamagnetic fraction was higher for Fe3O4-OA-MN and Fe3O4-PEG-MN compared to Fe3O4-MN studied using a Mossbauer spectrometer. Compared to the control, an increased killing (35%) was observed in human breast cancer cells (MCF7) after Fe3O4-OA-MN treatment, which was further enhanced (65%) under induction heating conditions. However, MCF7 cells treated with Fe3O4-MN or Fe3O4-PEG-MN showed 5–10% killing after induction heating. These results showed the characterization of MN with different lipophilicity and suggests their suitability for hyperthermia applications in cancer therapy.

Magnetic properties of single-domain SrFe12O19 particles synthesized by citrate precursor technique

Nanosize particles of SrFe12O19 have been synthesized by a citrate precursor technique with various Fe/Sr ratios of 12.0 to 9.0. X-ray diffraction (XRD) studies showed the formation of ultrafine, monophasic SrFe12O19 particles with comparable unit cell parameters. Magnetic clusters were observed by scanning electron microscopy and Branauer–Emmett–Teller surface area measurements. Mossbauer results reveal the ferrimagnetic and superparamagnetic nature and the change in hyperfine parameters with decline in particle size and Fe/Sr ratios. The magnetic properties of small SrFe12O19 particles (Fe/Sr=12.0) showed a considerable enhancement in TC from a bulk value of 750–883 K measured for 20–5.7 nm XRD particle size. The shift in Curie temperature is well defined by the finite size scaling formula [TC(D)−TC(∞)]TC(∞)−1=(D/D0)−1/ν with ν=0.75–0.02 and D0=1.52 nm. The change in Hic, σs, and σr values were observed with the decline in particle size and the Fe/Sr ratios where Hic of 6500 Oe is achieved for isotropic...

Carbogenic Nanodots: Photoluminescence and Room-Temperature Ferromagnetism

Herein, blue fluorescent carbogenic nanodots (CNDs) with room-temperature ferromagnetism were synthesized by thermal decomposition of organic precursors at different temperatures. Photoluminescence (PL) studies show excitation-wavelength-dependent emission properties and PL excitation (PLE) studies confirm the triplet ground state of carbene at the zigzag edge as the fluorescent center. Room-temperature magnetic studies reveal the ferromagnetic nature of CNDs and temperature-dependent studies show the presence of an antiferromagnetic phase along with a ferromagnetic phase below 50 K. EPR studies reveal the presence of conduction electrons and localized spins with different g factors. Localized spins at zigzag edges are the origin of the unconventional magnetic behavior, whereas exchange coupling between conduction and localized spins are responsible for long-range magnetic ordering.

Synthesis and magnetic studies of nanocrystalline nickel nitride material

Single domain Ni 3 N nitride particles are synthesized by simultaneous decomposition and nitridation in ammonia atmosphere of [Ni(NH 3 ) 6 ](NO 3 ) 2 complex crystals at 650 K. The Ni 3 N phase crystallizes in the hexagonal structure with unit cell parameters a = 4.624(4) A and c = 4.316(4) A, and has a crystallite size of 16 nm. In TEM study, these nanosize particles show spherical shape, and form particle aggregates of 18 nm size. Ni 3 N particles exhibit a Curie temperature of T C = 634 K. In the field dependence magnetic measurements, the presence of hysteresis loop indicates ferromagnetic behavior with σ s = 1.678 emu/g, σ R = 0.50 emu/g and μ 0 H c = 0.022 T. In this phase, the density of states (DOS) of Ni is dominated by 3d states and is mixed with 2p DOS of N. The contribution of d-electrons in the intra-band polarization affects the magnetic moment of Ni and thus the magnetic moment of Ni 3 N.

Magnetic‐Nanoparticle‐Doped Carbogenic Nanocomposite: An Effective Magnetic Resonance/Fluorescence Multimodal Imaging Probe

A novel and facile approach is developed to synthesize a magnetic nanoparticle (iron oxide)-doped carbogenic nanocomposite (IO-CNC) for magnetic resonance (MR)/fluorescence imaging applications. IO-CNC is synthesized by thermal decomposition of organic precursors in the presence of Fe(3) O(4) nanoparticles with an average size of 6 nm. IO-CNC shows wavelength-tunable fluorescence properties with high quantum yield. Magnetic studies confirm the superparamagnetic nature of IO-CNC at room temperature. IO-CNC shows MR contrast behavior by affecting the proton relaxation phenomena. The measured longitudinal (r(1) ) and transverse (r(2) ) relaxivity values are 4.52 and 34.75 mM(-1) s(-1) , respectively. No apparent cytotoxicity is observed and the nanocomposite shows a biocompatible nature. In vivo MR studies show both T(1) and T(2) * contrast behavior of the nanocomposite. Fluorescence imaging indicates selective uptake of IO-CNC by macrophages in spleen.

Experimental study of Hopkinson effect in single domain CoFe/sub 2/O/sub 4/ particles

Nanosize particles of CoFe/sub 2/O/sub 4/ have been synthesized by the citrate precursor technique. Considerably higher coercive force (1.68 kOe) than that obtained by the conventional technique (1.00 kOe) is associated with the nanostructure of CoFe/sub 2/O/sub 4/. These nanosize ferrimagnetic CoFe/sub 2/O/sub 4/ particles exhibit chainlike clusters indicating strong interparticle interactions and reduced magnetic moment, which is attributed to anisotropy and canted spin structure at the surface of the particle. The magnetization shows a peak just below the Curie temperature T/sub c/ during heating in the presence of a small magnetic field (the Hopkinson effect), On the other hand, the magnetization increases monotonically when the system is cooled from T/sub c/. This peak is associated with the single domain behavior of nanocrystalline CoFe/sub 2/O/sub 4/ particles and explained within the mathematical formalism given by Stoner and Wohlfarth in conjunction with other explanations of Hopkinson effect.

Synthesis and self-assembly of monodisperse CoxNi100−x (x = 50, 80) colloidal nanoparticles by homogenous nucleation

Self-assembled monodisperse fcc Co(50)Ni(50) and Co(80)Ni(20) alloy nanoparticles with the average size of 25 and 8 nm respectively are synthesized by reductive thermal decomposition of Co(II)(acac)(2) and Ni(II)(acac)(2) in the presence of surfactants such as oleic acid, oleylamine and trioctylphosphine. The mechanism for formation of colloidal CoNi alloy nanoparticles is explored in this work. The CoNi nanoparticles with high atomic percentage of nickel are found to be more stable and non-interacting. The Co(50)Ni(50) nanoparticles are superparamagnetic at room temperature and exhibit superparamagnetic to ferromagnetic transition at the blocking temperature (T(b)) ∼130-160 K, whereas Co(80)Ni(20) nanoparticles are ferromagnetic at room temperature with low coercivity (∼20 Oe). The magnetization value of Co(80)Ni(20) nanoparticles is found to be high as compared to Co(50)Ni(50) nanoparticles due to high atomic percentage of cobalt. Interestingly, size of CoNi alloy nanoparticles with high nickel content is found to be large, which indicates that nickel nuclei act as catalysts for the growth of CoNi alloy nanoparticles in the reaction.

Mössbauer and magnetic studies of nanocrystalline γ'-Fe4-xNixN (0.2 ≤ x ≤ 0.8) compounds

Abstract Nanocrystalline γ′-Fe4−xNixN (0.2⩽x⩽0.8) compounds were synthesized by using a citrate precursor route. It was observed that lattice constants for γ′-Fe4−xNixN (0.2⩽x⩽0.8), decrease with increasing Ni atom concentration. The atmospheric oxidation of γ′-Fe4−xNixN (0.2⩽x⩽0.8) compounds result in the formation of Fe-oxide layer at the surface of the ultrafine particles in addition to pure nitride phase. The local magnetic structures of the iron atoms in the nitride materials are quite similar to those found in the case of dilute alloy systems. The role of Ni substitution in γ′-Fe4N as γ-Fe4−xNixN is investigated with regard to crystal structure and magnetic properties of the ultrafine nitride materials. The results suggest that the average magnetic moment per iron atom in ultrafine γ′-Fe4−xNixN compounds is affected by the Ni atom concentrations, superparamagnetic relaxation, presence of oxide layer and randomly canted spin structure at the particle surface. The observed larger values of coercivities in the ultrafine materials are on account of the reversal of magnetization by spin rotation mechanism.

Synthesis of self-assembled monodisperse 3 nm FePd nanoparticles: Phase transition, magnetic study, and surface effect

Self-assembled monodisperse 3 nm face centered cubic (fcc) FePd particles are synthesized by modified polyol method using polyethylene glycol-600 as a reducing agent and oleic acid and oleyl amine as surfactants. As-synthesized FePd nanoparticles are superparamagnetic at room temperature and ferromagnetic below blocking temperature (TB=21 K). The significant enhancement in saturation magnetization is observed at 5 K. This is attributed to surface effect for 3 nm size particles. The nanoparticles are spherical with uniform dispersion as depicted in transmission electron microscopy study. The noninteracting behavior of as-synthesized FePd nanoparticles is verified through Langevin fit. The saturation magnetization (σs) and mean moment of (μm) particles are computed to be σs=22.73 emu/g and μm=4466μB, respectively. The ordered face centered tetragonal (fct) phase of composition Fe43Pd57 was obtained from disordered fcc FePd phase by annealing at 550 °C for 1 h under reducing atmosphere of (N2+H2) gas. The ha...

Antibiofilm and Membrane-Damaging Potential of Cuprous Oxide Nanoparticles against Staphylococcus aureus with Reduced Susceptibility to Vancomycin

ABSTRACT The antimicrobial effects of copper ions and salts are well known, but the effects of cuprous oxide nanoparticles (Cu2O-NPs) on staphylococcal biofilms have not yet been clearly revealed. The present study evaluated Cu2O-NPs for their antibacterial and antibiofilm activities against heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-intermediate S. aureus (VISA). Nanoscaled Cu2O, generated by solution phase technology, contained Cu2O octahedral nanoparticles. Field emission electron microscopy demonstrated particles with sizes ranging from 100 to 150 nm. Cu2O-NPs inhibited the growth of S. aureus and showed antibiofilm activity. The MICs and minimum biofilm inhibitory concentrations ranged from 625 μg/ml to 5,000 μg/ml and from 2,500 μg/ml to 10,000 μg/ml, respectively. Exposure of S. aureus to Cu2O-NPs caused leakage of the cellular constituents and increased uptake of ethidium bromide and propidium iodide. Exposure also caused a significant reduction in the overall vancomycin-BODIPY (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding and a decrease in the viable cell count in the presence of 7.5% sodium chloride. Cu2O-NP toxicity assessment by hemolysis assay showed no cytotoxicity at 625 to 10,000 μg/ml concentrations. The results suggest that Cu2O-NPs exert their action by disruption of the bacterial cell membrane and can be used as effective antistaphylococcal and antibiofilm agents in diverse medical devices.