Control over the synthesis of monodisperse silica particles up to mesoscopic scale is generally made difficult due to intrinsic limitation to submicrometric dimensions and secondary nucleation in seeded experiments. To investigate this issue and overcome these difficulties, we have implemented single step processing by quantifying the effects of the progressive addition of a diluted tetraethyl orthosilicate solution in ethanol on the size and monodispersity of silica particles. Contrary to particles grown in seeded polymerization, monodisperse particles with size up to 2 microm were synthesized. Moreover, the particles exhibit a final diameter (d(f)), which varies with V(-1/3) over more than 2 orders of magnitude in rate of addition (V). On the basis of a kinetic study in the presence of addition showing that particle growth is limited by the diffusion of monomer species, we developed a diffusion-limited growth model to theoretically explain the observed d(f)(V) behavior and quantitatively retrieve the measured amplitude and exponent. Using a single parameter procedure, we can therefore predict and generate in the room temperature range, monodisperse particles of a targeted size by simply adjusting the rate of addition.

In this work, we examine the mechanisms of heat production by whole intact cells of magnetotactic bacteria, Magnetospirillum magneticum strain AMB-1, as well as by their extracted chains of magnetosomes or extracted individual magnetosomes when they are exposed to an oscillating magnetic field of frequency 108 kHz and field amplitudes varied between 23 mT and 88 mT. For intact bacterial cells that contain chains of magnetosomes, heat is generated through hysteresis losses yielding specific absorption rates (SAR) of 110 W/gFe at 23 mT and 860 W/gFe at 88 mT. When the chains of magnetosomes are extracted from the bacterial cells and exposed to the same magnetic field, the heatproducing mechanism includes an additional contribution, one that is due to their rotation in the magnetic field. This results in the production of higher SAR of 860 W/gFe at 23 mT and 1240 W/gFe at 88 mT. Lower SAR values of 540 W/gFe at 23 mT and 970 W/gFe at 88 mT are obtained with the individual magnetosomes. This appears to be due to aggregation of the individual magnetosomes in the liquid, which prevents them from rotating as efficiently as the chains of magnetosomes.