Reverse Switching Phenomena in Hybrid Organic–Inorganic Thin Film Composite Material

A systematic approach was followed to develop a new hybrid organic–inorganic composite material with intriguing electrical and fluorescence properties into one ultrathin film system. Providing facile and cost-effective synthesis, this method utilizes a double decomposition reaction to introduce electric and fluorescence as an intrinsic property into one ultrathin film system, through dihydrolipoic acid-coated core/shell CdSe/ZnS quantum dots. Scanning tunneling microscope was used to asses, at the microstructured level, electrical properties of the composite material. Thin film composite devices exhibit higher conductivity with the application of a lower electrical field and inversely show lower conductivity when applying higher electrical bias point. The prospect of this feature solely lies in band gap engineering inherent to the device structure and geometric properties. The merits of such a device, paired with the ease of chemical functionalization provided by the water-soluble quantum dots, make the obtained hybrid organic–inorganic thin film composite material a viable candidate to be used as sensors, optolectronic devices, as well as pathogenic detectors

Magnetic Silica Nanoparticle Cellular Uptake and Cytotoxicity Regulated by Electrostatic Polyelectrolytes–DNA Loading at Their Surface

Magnetic silica nanoparticles show great promise for drug delivery. The major advantages correspond to their magnetic nature and ease of biofunctionalization, which favors their ability to interact with cells and tissues. We have prepared magnetic silica nanoparticles with DNA fragments attached on their previously polyelectrolyte-primed surface. The remarkable feature of these materials is the compromise between the positive charges of the polyelectrolytes and the negative charges of the DNA. This dual-agent formulation dramatically changes the overall cytotoxicity and chemical degradation of the nanoparticles, revealing the key role that surface functionalization plays in regulating the mechanisms involved

High-Temperature Magnetism as a Probe for Structural and Compositional Uniformity in Ligand-Capped Magnetite Nanoparticles

To investigate magnetostructural relationships in colloidal magnetite (Fe₃O₄) nanoparticles (NPs) at high temperature (300–900 K), we measured the temperature dependence of magnetization (<i>M</i>) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of <i>M</i> for these NPs, with dip and loop features observed during heating–cooling cycles. Detailed characterizations of as-synthesized and annealed Fe₃O₄ NPs as well as reference ligand-free Fe₃O₄ NPs indicate that both types of features in <i>M</i>(<i>T</i>) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe³⁺ to Fe²⁺ and the associated dip in <i>M</i>, leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent <i>M</i> curves featuring loops. The increase in <i>M</i> with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe³⁺/Fe²⁺ ratio with heat treatment. The interpretation of irreversible features in <i>M</i>(<i>T</i>) indicates that reversible <i>M</i>(<i>T</i>) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature <i>M</i>(<i>T</i>) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials