Nanocrystal molecules

An equally important challenge for nanocrystal assembly is the fonnation of specific nanocrystal arrangements in solution. By using complementary DNA strands as tethers, Mirkin et al [102, 103] fonned aggregates of gold nanocrystals with specific sizes Alivisatos et al also used DNA to stmcture semiconductor nanocrystal molecules, though in this case the molecules contained only a few nanocrystals placed controlled distances from each other [104, 105 and 106]. The potential applications of biomolecular teclmiques to this area of nanoscience are immense, and the opportunities have been reviewed in several recent publications [107, 108, 109 and 110]. 

Alivisatos AP, Peng X, Wilson TE, Loweth CL, Bruchez MPJ, Schultz PG (1996) Organization of nanocrystal molecules using DNA. Nature 382 609-611... 

Development of Nanocrystal Molecules for Plasmon Rulers and Single Molecule Biological Imaging... 

Summary. Nanocrystals play an increasingly important role as labels in biological imaging. This chapter considers distinct groupings of nanocrystals, termed nanocrystal molecules, in which the individual nanocrystals are plasmonically coupled. These new structures can be used to investigate biomolecular dynamics. 

Our goal then is clear, to construct nanocrystal molecules in which noble metal nanoparticles of 10-40 nm diameter are joined together using oligonucleotides or peptides, and to observe the light scattering from single molecules... 

Over the last decade, we have shown that DNA can be used to construct a wide range of such nanocrystal molecules. The first such example of using DNA to organize nanocrystal molecules was shown in 1996 by Alivisatos and Schultz [12] (Fig. 9.4). This work appeared simultaneously with the work by Mirkin and Letsinger, who used DNA to assemble arrays of nanoparticles [13]. Indeed, if the nanocrystal is thought of as an artificial atom, then the construction of artificial solids is a complementary activity to the construction of artificial molecules, and this has been investigated extensively as well [14]. 

The plasmon rulers shown here can be extended to work in vivo as well. We have recently developed nanocrystal molecules joined together by peptides, and we have shown that their light scattering can be detected when the particles are introduced into the cytoplasm of living cells. Further, we have shown that we can detect the cleavage of the peptides when specific byproteases are activated [20]. 

Fig. 9.9. Gallery of nanocrystal molecules prepared by inorganic routes, rattier than by biological assembly. These nanocrystal molecules can be branched or chained, as well as be hollow and nested. They can be coupled together electronically, as opposed to through space by plasmon coupling...

In the work described here, we see one specihc class of new nanostructure, nanocrystal molecules joined by DNA or peptides. The coupling between the particles is due to plasmon coupling. We can envision other t3rpes of nanocrystal molecule, in which the coupling between the particles arises, for instance, by direct electronic coupling. To achieve such goals, we need to make... 

Recently, many scientists and engineers have looked for methods to control the sizes of QDs and make possible the formation of ordered lateral two-dimensional superlattices or vertical superlattices for heterojunction thin films. One approach is the top-down method, molecular beam epitaxy nanolithographic technology, which has been developed with the development of microelectronics and processing techniques for traditional inorganic semiconductors. This technique of nanoscale manipulation can reach only the upper limits of sizes defined by nanostructure physics, and has successfully manipulated artificial atoms and molecules [10-12). Bottom-up method is based on molecular and supramolecular assembly techniques that have been proposed by chemists in recent years. With this method, it is possible to prepare monodispersed defect-free nanocrystal QDs 1-10 nm in size and to control easily QDs coupling to form nanocrystal molecules, even quantum dot superlattices in two or three dimensions. 

Dufresne Alain. Processing of polymer nanocomposites reinforced with polysaccharide nanocrystals. Molecules. 15 no. 6 (2010) 4111-4128. 

Deepa B, Abraham E, Cherian BM, Bismark A, Blaker JJ, Pothan LA, Leao AL, de Souza SE, Kottaisamy M (2011) Structure, morphology and thermal characteristies of banana nano fibers obtained by steam explosion. Bioresour Technol 102(2) 1988-1997 Dufresne A (2010) Processing of Polymer Nanocomposites Reinforced with Polysaccharide Nanocrystals. Molecules 15 4111-4128... 

The bottom-up approach is copied from nature and utilizes the profound knowledge gained in the selforganization of molecular assemblies and nanocrystals. Molecules and nanocrystals with different functionalities... 

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