Indocyanine green (ICG) is a fluorescence dye that is widely used for near-infrared imaging. Application of this dye is limited by its numerous disadvantageous properties in aqueous solution, including its concentration-dependent aggregation, poor aqueous stability in vitro and low quantum yield. Additionally, ICG is highly bound to nonspecific plasma proteins, leading to rapid elimination from the body with a half-life of 3-4 min. In this study, encapsulation of ICG within various micellar systems was investigated with the aim of overcoming these limitations. The aggregation behavior of different aqueous ICG formulations was studied using cryogenic transmission electron microscopy (cryo-TEM) and absorption spectroscopy. The micellar systems were characterized by their optical properties, particle size distribution, zeta potential and hemolytic activity. Encapsulation efficiency was determined using analytical ultracentrifugation. The best results were achieved for ICG encapsulated within aqueous Solutol HS 15 micelles. This formulation exhibited a lower aggregation behavior, a 3-fold increased quantum yield and high aqueous stability (over 4 weeks) compared to free aqueous ICG. The micelles were found to have an average diameter of 12 nm and a zeta potential close to zero (-2.1 +/- 1.7 mV). Encapsulation efficiency of ICG was high at 95%. The formulation did not display significant hemolytic activity. Consequently, Solutol HS 15 micelles are suitable nanocarriers for ICG which improve the optical properties and stability of the dye.
Spherical polystyrenesulfonate particles in the size range between 7 nm<R<50 nm are synthesized via crosslinking copolymerization in microemulsion and subsequent sulfonation via polymer reactions. These model polyelectrolytes, when carefully purified, show the qualitative aspects of the polyelectrolyte effect, i.e., large excess viscosities with a strong increase of the intrinsic viscosity with decreasing concentration. A quantitative evaluation of these data on the basis of a modified Hess–Klein relation reveals that the complete dependence on polymer as well as on salt concentration can be fitted with one parameter only, the effective charge number per particle, Zeff. The specific viscosity increases with decreasing particle size and inverse particle density, but no simple explanations for the found relations can be given. Since conformational changes play only a minor role for spherical systems, the comparison of the concentration dependence of the reduced viscosities of linear chains with those of the spherical polyelectrolytes allows for a differentiation between intra- and intermolecular effects. It is qualitatively shown that a major contribution to the polyelectrolyte effect is caused by intermolecular interactions, i.e., the increase of the electrostatic screening length and interparticle-coupling with decreasing concentration. The quantitative description of the concentration and molecular weight dependence of the reduced viscosity of linear polyelectrolytes in salt-free solution reveals that Zeff does apparently not depend on molecular weight, the found molecular weight dependence of the reduced viscosity is due to the increase of the hydrodynamic radius, only. In addition, our modified Hess–Klein model also describes some quantitative features of the viscosity curves, such as the molecular weight dependent shape of the maxima. Deviations between theoretical description and experimental data which become significant for smaller linear polyelectrolytes are attributed to a concentration dependent coil expansion.
The magnetic particle spectrum (MPS) of bacterial magnetosomes, isolated from Magnetospirillum gryphiswaldense, is measured and compared to that of the current "gold standard", Resovist®. It is shown that the amplitudes of the magnetosomes' harmonics by far exceed that of Resovist®; the amplitude of the third harmonic is higher by a factor of 7, and is the highest value obtained for iron oxide nanoparticles to date.
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