Coated magnetite nanoparticles with a 6−8 nm average diameter were prepared. The surfactants used to stabilize the nanoparticles and disperse them in organic solvents were oleic acid (OA), lauric acid , dodecyl phosphonate, hexadecyl phosphonate, and dihexadecyl phosphate. Transmission electron microscopy analyses of the aggregation of the coated particles suggest that carboxylate surfactants provide the particles with better isolation and dispersibility as compared with phosphonate surfactants. However, Fourier transform infrared spectra of the phosphonate and phosphate coated particles suggest that these surfactants cover the surface of the nanoparticles in islands of high packing density. The thermogravimetric and differential scanning calorimetry measurements suggest that there is a quasi-bilayer of these surfactants covering the surface of the nanoparticles, with varying amounts of surfactant in the outer layer and with the second layer weakly bound to the primary layer through hydrophobic interactions between the alkyl chains. The desorption temperatures of the alkyl phosphonates and phosphate are higher than those of the carboxylate coated particles. The enthalpy of binding of the ligands suggests strong P−O−Fe bonding on the surface. Nevertheless, regardless of binding strength, the OA coated particles are better dispersed in organic solvents. Their higher hydrophobicity is likely due to different interactions among the oleyl chains and/or a smaller tendency to form bilayer structures.

Uniform 2D arrays of organically passivated magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) have been prepared by the Langmuir–Blodgett technique. Preliminary studies of the magnetization curves show small changes in the shape of the curves depending on the number of deposited layers. Control over the formation of the colloidal solutions and of the 2D arrays, combined with the possibility to tune the physical properties of these arrays, may lead to new information storage media as well as novel magnetoresistive materials.

Colloidal Ag nanoparticles coated with L‐glutathione attached to bimane chromophores were studied by absorption, circular dichroism (CD), and fluorescence spectroscopies. The absorption and CD spectra were resonantly enhanced by Ag surface plasmons. The wavelength and particle‐size dependence of the enhancement indicated that an electromagnetic “antenna” effect is in action.

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