Silica coated iron nanoparticles: synthesis, interface control, magnetic and hyperthermia properties.

This work provides a detailed study on the synthesis and characterization of silica coated iron nanoparticles (NPs) by coupling Transmission Electronic Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and magnetic measurements. Remarkably, iron NPs (of 9 nm of mean diameter) have been embedded in silica without any alteration of the magnetization of the iron cores, thanks to an original protocol of silica coating in non alcoholic medium. Tuning the synthesis parameters (concentration of reactants and choice of solvent), different sizes of Fe@SiO2 composites can be obtained with different thicknesses of silica. The magnetization of these objects is fully preserved after 24 h of water exposure thanks to a thick (14 nm) silica layer, opening thus new perspectives for biomedical applications. Hyperthermia measurements have been compared between Fe and Fe@SiO2 NPs, evidencing the self-organization of the free Fe NPs when a large amplitude magnetic field is applied. This phenomenon induces an increase of heating power which is precluded when the Fe cores are immobilised in silica. High-frequency hysteresis loop measurements allowed us to observe for the first time the increase of the ferrofluid susceptibility and remanence which are the signature of the formation of Fe NPs chains.

Monitoring brain function during cardiothoracic surgery in children and adults at two levels of hypothermia.

The EEGs of 9 infants and 9 adults undergoing cardiac surgery were analysed during 2 different temperature ranges. Variance analysis showed that there were very significant interactions between age and temperature effects (P less than 0.01) and between temperature and specific frequency bands (P less than 0.005). These interactions were studied further and the greatest changes were discovered in the infant group when the temperature fell from the upper to the lower hypothermic range: low delta activity increased significantly while those of alpha and theta fell significantly. The significant quantitative differences found in this study agree with qualitative observations from other reports.

Monitoring EEG frequency and amplitude during cardiac surgery.

Changes in the electroencephalograms of patients undergoing cardiac surgery with cardiopulmonary bypass were studied. An analysis technique with a simple display of amplitude and frequency within the traditional bands was used. During the course of an operation, there can be dramatic changes in frequency contribution with little or no change in overall EEG amplitude. Evaluation of the results shows that this technique clearly draws attention to periods of EEG change, and examples are given.

Comparison of EEG monitoring techniques: an evaluation during cardiac surgery.

A single channel EEG recording was made in 25 patients undergoing cardiac surgery and analysed using 5 different techniques--amplitude, cerebral function monitor, Fourier, Hjorth, and zero-crossing analyses. The results of the analyses were plotted as trend information on paper. These trends were studied for changes in the EEG during surgery. In the majority of cases changes were noted simultaneously by all 5 techniques. There were, however, some cases in which an amplitude-only technique showed no changes while frequency contributions were changing, and a frequency-only technique showed no changes while amplitudes were changing. The conclusion drawn is that major EEG changes are observed with any of the techniques studied, but that for improved sensitivity a technique analysing both frequency and amplitude information should be used.