Diffusion of nanoparticles

Cytoplasm is an important target for si RNA and antisense oligonucleotides whereas transcription factors and plasmid DNA should be delivered into the nucleus (Figure 22.2). Cytoplasm is a highly viscous medium where passive diffusion of nanoparticles, and macromolecules are very slow [27]. It is very appealing to search for the means by which the nanoparticulate transport in the cytoplasm and delivery into the nucleus can be maximized [28]. Specific nuclear localizing peptides have been attached to the nanoparticulates for the nuclear delivery but their efficacy is still not adequate [29]. 

Jang and Choi [39] devised a theoretical model that includes four modes of energy transport the collision between basefluid molecules, the thermal diffusion of nanoparticles in the fluid, the collision between nanoparticles due to Brownian motion, and the thermal interactions of dynamic nanoparticles with base fluid molecules. 

Kihm KD, Banerjee A, Choi CK, Takagi T (2004) Near-wall hindered Brownian diffusion of nanoparticles examined by three-dimensional ratiometric total internal reflection fluorescence microscopy (3-D R-TIRFM). Exp Fluid 37 811-824... 

Jang and Choi [26] numerically investigated the cooling performance of a microchannel heat sink with nanofluids. Two kinds of nanofluids were investigated in this study, i.e., d = 6 nm nanoparticles in a copper-water mixture and dp = 2 nm diamond-in-water nanofluid. A theoretical model was employed for the thermal conductivity of nanofluids that accounts for four modes of energy transport the thermal diffusion in the base fluid, the thermal diffusion of nanoparticles, the collision between the nanoparticles, and the nanoconvection due to Brownian motion. Specifically,... 

FCS studies were not only performed in PNIPAM, but also in thermoresponsive poly(2-oxazolines) [150] and to investigate the diffusion of nanoparticles in meth-ylcellulose [151]. At low temperature, the latter exhibits a transient polymer mesh networks in the fluid state which at higher temperatures switches to a gelled state due to a formation of fibrillar structures. 

Omari RA, Aneese AM, Grabowski CA, Mukhopadhyay A (2009) Diffusion of nanoparticles in semidilute and entangled polymer solutions. J Phys Chem B 113(25) 8449-8452... 

Another way to obtain a gradient of particle concentration consists of spin casting or solution casting the nanoparticles in a colloidal solution on top of the spin cast polymer film. Diffusion of nanoparticles into the polymer matrix takes place with a penetration depth that is controlled by the temperature. To enhance the diffusion solvents can be used that swell the polymer layer, though not dissolving it. By varying the spin and solution casting conditions various diffusion profiles can be obtained. 

In summary, suppressed diffusion of nanoparticles in highly viscous media, such as ionic liquids, leads to an increase in the lifetime by a factor of 10-1000 comp>ared to classic low viscous solvents, contributing significantly to the stabilization of colloidal nano-sized particles. As mentioned above, ionic liquids can also serve as electrostatic and steric stabilizers. The physicochemical properties of ionic liquids and, thus, the properties of ionic liquid stabilized nanoparticles can be readily adjusted by changing cations and anions. Compared to polymers, ionic liquids as stabilizers for nanoparticles provide some particular advantages. Non-ionic polymers (in contrast to polyelectrolytes) have no ionic nature (only steric stabilization applies) and their ability to dissolve various compounds, for instance, metal precursors or substrates is limited vide infra). Thus, often an orj nic solvent is required, where both polymer, metal precursor and the substrate are soluble e.g., in case of applications in catalysis). The use of organic solvents can be avoided, when catalytic reactions are performed in neat ionic liquids (with dispersed nanoparticles). Reactions can also be conducted in neat substrate, where small amount of ionic liquid stabilized nanoparticles are added. 

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett, 95, 107401-1-107401-4 Tang, J. and Marcus, R. A. (2005) Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots./. Chem. Phys., 123,054704-1-054704-12. 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett., 95, 107401. 

In general, homogeneous nucleation of nanoparticles occurs when a solute (C) diffuses to surface of a cluster from a bulk solution, and then incorporates into the cluster through surface reaction until a nucleus (C ) is obtained ... 

A similar technique, the so-called spontaneous emulsification solvent diffusion method, is derived from the solvent injection method to prepare liposomes [161]. Kawashima et al. [162] used a mixed-solvent system of methylene chloride and acetone to prepare PLGA nanoparticles. The addition of the water-miscible solvent acetone results in nanoparticles in the submicrometer range this is not possible with only the water-immiscible organic solvent. The addition of acetone decreases the interfacial tension between the organic and the aqueous phase and, in addition, results in the perturbation of the droplet interface because of the rapid diffusion of acetone into the aqueous phase. 

Organic polymers are very often used for the stabilization of metal nanoparticles by providing a steric stabilizing effect Due to this embedding effect, it is generally considered that the diffusion of substrates through the polymer matrix can be limited. Nevertheless, some interesting results have been obtained. 

The high photostability of the nanoparticle originates from protection provided by the silica matrix for the embedded fluorophores. Environmental oxygen is a universal quencher for fluorophores in aqueous solution and the network structure of the silica matrix reduces diffusion of environmental oxygen to the fluorophores. Thus, the photostability of embedded fluorophores is greatly improved [3]. 

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