We report a facile synthesis of cube-shaped Co x Fe3–x O4 nanocrystals (NCs), which could be finely tuned in terms of NC size (from 15 to 27 nm) and cobalt stoichiometry (from 0.1 to 0.7). These particles exhibited high specific absorption rate (SAR) values, relevant for magnetic hyperthermia, and high relaxivity values, significant for magnetic resonance imaging applications. The peculiarity of these NCs is that already at low frequencies (such as 105 kHz, a working frequency used on human patients), they display SAR values that are three-times as large as those of iron oxide nanocubes of comparable sizes (and which were already considered outstanding). The highest SAR value recorded on the NCs reported here (915 ± 10 W/g(Co+Fe) at 105 kHz and 32 kAm–1) refers to particles with cubic shape, 20 ± 2 nm edge size, and Co stoichiometry between 0.6 and 0.7. The highest r 2 value (958 mM–1 s–1) was instead recorded on nanocubes with Co stoichiometry around 0.5/0.6 and size of 20 ± 2 nm. Remarkably, only at this specific size and Co stoichiometry were the NCs not perfect cubes but had a slightly concave shape, which together with their core–shell structure and magnetic parameters might account for the higher r 2 values recorded. NCs reported here, with optimized SAR and r 2 values, are promising tools for theranostic applications.
The interactions between noncancerous, primary endothelial cells and gold nanoparticles with different morphologies but the same ligand capping are investigated. The endothelial cells are incubated with gold nanospheres, nanorods, hollow gold spheres, and core/shell silica/gold nanocrystals, which are coated with monocarboxy (1-mercaptoundec-11-yl) hexaethylene glycol (OEG). Cell viability studies show that all types of gold particles are noncytotoxic. The number of particles taken up by the cells is estimated using inductively coupled plasma (ICP), and are found to differ depending on particle morphology. The above results are discussed with respect to heating efficiency. Using experimental data reported earlier and theoretical model calculations which take into account the physical properties and distribution of particles in the cellular microenvironment, it is found that collective heating effects of several cells loaded with nanoparticles must be included to explain the observed viability of the endothelial cells.
The interactions between skin and colloidal gold nanoparticles of different physicochemical characteristics are investigated. By systematically varying the charge, shape, and functionality of gold nanoparticles, the nanoparticle penetration through the different skin layers is assessed. The penetration is evaluated both qualitatively and quantitatively using a variety of complementary techniques. Inductively coupled plasma optical emission spectrometry (ICP-OES) is used to quantify the total number of particles which penetrate the skin structure. Transmission electron microscopy (TEM) and two photon photoluminescence microscopy (TPPL) on skin cross sections provide a direct visualization of nanoparticle migration within the different skin substructures. These studies reveal that gold nanoparticles functionalized with cell penetrating peptides (CPPs) TAT and R7 are found in the skin in larger quantities than polyethylene glycol-functionalized nanoparticles, and are able to enter deep into the skin structure. The systematic studies presented in this work may be of strong interest for developments in transdermal administration of drugs and therapy.
We present the exocytosis profile of two types of peptide-coated nanoparticles, which have similar charge and size but different functionality. While one kind of particles appears to progressively exocytose, the other one has a more complex profile, suggesting that some of the particles are re-uptaken by the cells. Both types of particles retain their colloidal stability after exocytosis.Understanding the interactions of functional nanoparticles with biological cells is of tremendous importance not only for new developments in sensing, imaging and therapy but also for realizing the fundamental cellular mechanisms and cytotoxicity of nanomaterials.1-5 With an accumulated knowledge of how the size, shape and functionality of nanomaterials influence their fate in cells, one should be able to synthesize nanoparticles on demand, with appropriate functionality and which are best suited to a particular application. This means that particles would be designed to (a) be taken up by the cell in desirable numbers, (b) deliberately escape from the endosomes, (c) access the cytoplasm and migrate selectively through the cell for a given time, (d) target specific compartments and organelles (i.e. nucleus, mitochondria) to perform desired tasks and (e) exocytose in high numbers leaving the cell intact. Following these aims, several research groups have successfully investigated various aspects of interactions between functional nanoparticulate systems and cells.6-14 For example, Brust and co-workers shed light on the intracellular fate of spherical gold nanoparticles coated with cell penetrating peptides and suggested ways of pre-programming nanoparticle migration within the cytoplasm.15,16 Alternatively Mirkin and colleagues performed a systematic study on the internalization rate of DNA modified gold nanoparticles and suggested new directions for targeted gene therapy.17,18 Our group and others have investigated how the size, shape and charge of nanoparticles influence their cellular uptake, [19][20][21][22][23] and how the number of endocytosed particles correlates with the nanoparticles' heating efficiency during laser hyperthermia. 20,24Despite the extensive work on gold nanoparticle uptake and intracellular fate, 7,25 a very limited number of papers have discussed the exocytosis of functional gold nanoparticles. 26 Since gold is one of the most promising candidates for biomedical applications in the near future, exocytosis studies are of great importance, because they are directly correlated with chronic cytotoxicity and nanoparticle intracellular retention times.In this paper we investigated the cellular uptake and exocytosis of two types of peptide functionalized gold nanospheres by an important category of mammalian cells, namely human endothelial cells (HUVECs). The specific types of particles were chosen due to their ease of preparation and particular function. To keep our studies consistent, both types of nanoparticles were designed to have similar hydrodynamic size and charge. The first batch of nanoparticles ('inh...
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