Nanopartide aggregation

AMP) (20), bridged through a hybridization of the (21)-nudeic acid-functionalized CdSe/ZnS QDs and the (22)-nucleic acid-functionalized Au nanopartides, led to QD-Au nanopartide aggregates in which the fluorescence of the QDs was quenched by the gold nanopartides (Figure 6.20a). In the presence of AMP, the aptamer-AMP... 

A simple and economical method to achieve stable water-soluble iron oxide nanopartides is based on dispersions in an ionic liquid containing acrylic add anion. Distinct particles were synthesized by an organic phase decomposition method. The synthesis of magnetite nanopartides in our laboratories was carried out only by simple precipitation of ferrous salts in alkaline aqueous solutions at low temperature. It was found that the ionic liquid can be used as solvent and stabilizer to effidently tune the particle growth and prevent nanopartide aggregation (Zhai et al., 2009). 

Radomski, A. et al. (2005) Nanopartide-induced platelet aggregation and vascular thrombosis. British Jornal of Pharmacology, 146 (6), 882-893. 

Figure 8.4 Nano-Ti02 in fafade run-off (a, b) and in an urban stream (c). Single nanopartides or small matrix-bound aggregates have been found. Reprinted from [7], (2008), with permission from Elsevier.

Molecular self-organization in solution depends critically on molecular structural features and on concentration. Molecular self-organization or aggregation in solution occurs at the critical saturation concentration when the solvency of the medium is reduced. This can be achieved by solvent evaporation, reduced temperature, addition of a nonsolvent, or a combination of all these factors. Solvato-chromism and thermochromism of conjugated polymers such as regioregular polythiophenes are two illustrative examples, respectively, of solubility and temperature effects [43-45]. It should therefore be possible to use these solution phenomena to pre-establish desirable molecular organization in the semiconductor materials before deposition. Our studies of the molecular self-assembly behavior of PQT-12, which leads to the preparation of structurally ordered semiconductor nanopartides [46], will be described. These PQT-12 nanopartides have consistently provided excellent FETcharacteristics for solution-processed OTFTs, irrespective of deposition methods. 

A nonmetallic element, silicon, was prepared sonodiemically by reducing tetraethyl orthosilicate (TEOS) with a colloidal solution of sodium. The product was obtained as 2-5 nm sized, highly aggregated partides. The silicon exhibited a luminescence similar to that of porous silicon. This procedure is suggested as a general sonochemical reduction leading to the formation of metallic nanopartides [26]. 

C., Schiffrin, D.J., Antoine, R., Broyer, M., and Brevet, P.F. (2007) Second harmonic generation response by gold nanopartides at the polarized water/2-octanone interface from dispersed to aggregated partides. Journal of Physics. Condensed Matter, 19, 375108. 

Faulds, K., litdeford, R.E., Graham, D., Dent, G., and Smith, W.E. (2004) Comparison of surface-enhanced resonance Raman scattering from unaggrcgarcd and aggregated nanopartides. Analytical Chemistry, 76, 592-598. 

Many nanopartide preparations lack suffident stability (above. Fig. 11.5) to allow the ordered assembly of two-dimensional or three-dimensional materials and structures, in which the particles are dosely packed, without the onset of uncontrolled aggregation (agglomeration). To overcome this problem, the partides must be rendered chemically stable, for example by ligand stabilization, also to avoid degradation processes such as partial oxidation or undesired sintering of particles [11.6]. 

The main common characteristic of colloidal particles is their small size (typically 1 to 10 nm). The size of nanopartides in solution is dynamic and continuous redistribution in size can occur. In most cases, agglomeration leads to the formation of less active larger metal partides and this process may end in predpitation of larger crystals (palladium black). The per-atom catalytic efSdency of metal par-tides increases as the partide size decreases however, the probability of colloid agglomeration increases as their size decreases. To prevent agglomeration (and aggregation), and to preserve the finely dispersed state of the original partides, colloids are often prepared in the presence of stabilizers that adsorb onto the partide surface. 

A magnetic field, when applied perpendicularly to the substrate, induces the formation of 2-D hexagonal superlattices of individual Co nanoparticles [30] Pileni et al. [28] observed the formation of a hexagonal network of about 1 [tm dot-shaped aggregates made from 8nm cobalt nanopartides. CoPts nanociystals (4nm), when deposited under a magnetic field of 0.9 Tapplied perpendicularly to the substrate, can... 

Figure 6.20 (a) Analysis of adenosine monophosphate (AMP) by fluorescence quenching of functionalized QDs by gold nanopartides. The anti-adenosine monophosphate aptamer 20 bridges the CdSe QD functionalized with nucleic acid 21 and the nucleic acid 14-modifled with gold nanopartides to form the respective aggregate. 

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