The chemical and structural properties of ferrite-based nanoparticles, precursors for magnetic drug targeting, have been studied by Raman confocal multispectral imaging. The nanoparticles were synthesised as aqueous magnetic fluids by co-precipitation of ferrous and ferric salts. Dehydrated particles corresponding to co-precipitation (CP) and oxidation (OX) steps of the magnetic fluid preparation have been compared in order to establish oxidation-related Raman features. These are discussed in correlation with the spectra of bulk iron oxides (magnetite, maghemite and hematite) recorded under the same experimental conditions. Considering a risk of laser-induced conversion of magnetite into hematite, this reaction was studied as a function of laser power and exposure to oxygen. Under hematite-free conditions, the Raman data indicated that nanoparticles consisted of magnetite and maghemite, and no oxyhydroxide species were detected. The relative maghemite/magnetite spectral contributions were quantified via fitting of their characteristic bands with Lorentzian profiles. Another quality parameter, contamination of the samples with carbon-related species, was assessed via a broad Raman band at 1580 cm(-1). The optimised Raman parameters permitted assessment of the homogeneity and stability of the solid phase of prepared magnetic fluids using chemical imaging by Raman multispectral mapping. These data were statistically averaged over each image and over six independently prepared lots of each of the CP and OX nanoparticles. The reproducibility of oxidation rates of the particles was satisfactory: the maghemite spectral fraction varied from 27.8 +/- 3.6% for the CP to 43.5 +/- 5.6% for the OX samples. These values were used to speculate about the layered structure of isolated particles. Our data were in agreement with a model with maghemite core and magnetite nucleus. The overall oxidation state of the particles remained nearly unchanged for at least one month.

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We report here the development of stable aqueous suspensions of biocompatible superparamagnetic iron oxide nanoparticles (SPIONs). These so-called ferrofluids are useful in a large spectrum of modern biomedical applications, including novel diagnostic tools and targeted therapeutics. In order to provide prolonged circulation times for the nanoparticles in vivo, the initial iron oxide nanoparticles were coated with a biocompatible polymer poly(ethylene glycol) (PEG). To permit covalent bonding of PEG to the SPION surface, the latter was functionalized with a coupling agent, 3-aminopropyltrimethoxysilane (APS). This novel method of SPION PEGylation has been reproduced in numerous independent preparations. At each preparation step, particular attention was paid to determine the physico-chemical characteristics of the samples using a number of analytical techniques such as atomic absorption, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, transmission electron microscopy (TEM), photon correlation spectroscopy (PCS, used for hydrodynamic diameter and zeta potential measurements) and magnetization measurements. The results confirm that aqueous suspensions of PEGylated SPIONs are stabilized by steric hindrance over a wide pH range between pH 4 and 10. Furthermore, the fact that the nanoparticle surface is nearly neutral is in agreement with immunological stealthiness expected for the future biomedical applications in vivo.

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The aim of this work is to present a surface-enhanced Raman scattering (SERS) spectroscopic approach to study complexes of a frequently used antineoplastic agent, doxorubicin (DOX), with ferrous ions, at sub-micromolar concentrations in aqueous solution. The SERS bands of DOX were assigned according to critical analysis of literature. Prior to the complexation study, the spectral changes related to the drug orientation on the silver surface and to its protonation state were highlighted. The SERS spectra of DOX-Fe(2+) complexes showed several features distinguishing them from the free drug, protonated or not on the phenolic part of its chromophore. The lowest detectable content of the DOX-iron complex in the presence of free DOX was estimated to be 5-10%. This property is particularly interesting from the analytical point of view, since it allows for study of drug-iron interactions upon the drug loading on and release from magnetic drug carriers based on superparamagnetic iron oxide nanoparticles (SPIONs), stabilized with citrate ions or coated with polyethylene glycol (PEG) polymer. Our SERS data indicate that the drug loaded on magnetic nanocarriers as DOX-iron chelate was mainly released in the free DOX form. These results demonstrate the strength of the SERS approach for the study of DOX-iron interactions in relation to delivery issues and drug action mechanisms.