Progressive freezing of interacting spins in isolated finite magnetic ensembles.

Self-organization of magnetic nanoparticles into secondary nanostructures provides an innovative way for designing functional nanomaterials with novel properties, different from the constituent primary nanoparticles as well as their bulk counterparts. Collective magnetic properties of such complex closed packing of magnetic nanoparticles makes them more appealing than the individual magnetic nanoparticles in many technological applications. This work reports the collective magnetic behaviour of magnetic ensembles comprising of single domain Fe3O4 nanoparticles. The present work reveals that the ensemble formation is based on the re-orientation and attachment of the nanoparticles in an iso-oriented fashion at the mesoscale regime. Comprehensive dc magnetic measurements show the prevalence of strong interparticle interactions in the ensembles. Due to the close range organization of primary Fe3O4 nanoparticles in the ensemble, the spins of the individual nanoparticles interact through dipolar interactions as realized from remnant magnetization measurements. Signature of super spin glass like behaviour in the ensembles is observed in the memory studies carried out in field cooled conditions. Progressive freezing of spins in the ensembles is corroborated from the Vogel-Fulcher fit of the susceptibility data. Dynamic scaling of relaxation reasserted slow spin dynamics substantiating cluster spin glass like behaviour in the ensembles.

Direct one-pot synthesis of glutathione capped hydrophilic FePt-CdS nanoprobe for efficient bimodal imaging application.

One-pot synthesis methods for development of hydrophilic imaging nanoprobes have advantages over multi-pot methods due to their simple procedures, less probability for degradation of efficiency, superior control over growth and morphology, cost effectiveness, improved scope for scale-up synthesis etc. Here, we present a novel one-pot facile synthesis of hydrophilic colloidal bimodal nanoprobe (FePt-CdS) prepared through a seed-mediated nucleation and growth technique. In this facile synthesis of complex nanostructure, glutathione (GSH) was used as the capping agent to render biocompatibility and dispersibility. The microstructure, surface, optical, magnetic, biocompatibility, relaxivity and imaging property of the developed nanoprobe have been studied. The microstructural characterizations reveal average size of the particle as ~9-11nm with bleb shaped morphology. Spectroscopic characterization depicts the development of GSH capped CdS QDs on FePt, surface functionalities and their stability. The magnetic measurements confirm the superparamagnetic property in the developed bimodal nanoprobe. In addition, the GSH capping imparts excellent biocompatibility, water dispersibility, and fluorescence property to the probe. In RAW 264.7 macrophage cells, the bimodal nanoprobes exhibit intense green and red fluorescence. The magnetic resonance imaging (MRI) and fluorescence imaging (FI) study depict high transverse relaxivity and visible range fluorescent property in the synthesized FePt-CdS nanoprobe. Hence, the developed bimodal nanoprobe can be used as a potential candidate in simultaneous FI and MR imaging.

Mesoporous magnetic secondary nanostructures as versatile adsorbent for efficient scavenging of heavy metals.

Porous magnetic secondary nanostructures exhibit high surface area because of the presence of plentiful interparticle spaces or pores. Mesoporous Fe3O4 secondary nanostructures (MFSNs) have been studied here as versatile adsorbent for heavy metal scavenging. The porosity combined with magnetic functionality of the secondary nanostructures has facilitated efficient heavy metal (As, Cu and Cd) remediation from water solution within a short period of contact time. It is because of the larger surface area of MFSNs due to the porous network in addition to primary nanostructures which provides abundant adsorption sites facilitating high adsorption of the heavy metal ions. The brilliance of adsorption property of MFSNs has been realized through comprehensive adsorption studies and detailed kinetics. Due to their larger dimension, MFSNs help in overcoming the Brownian motion which facilitates easy separation of the metal ion sorbed secondary nanostructures and also do not get drained out during filtration, thus providing pure water.