Fluorescence, nanoparticles

The exploitation of the above expression systems in FRET requires the coherent selection of donor and acceptor moieties, from both the spectroscopic and biological perspective relative expression levels, compartmentalization, and temporal evolution of the system under study. Very advantageous are combinations of small fluorophores with VFPs, as well as with fluorescent nanoparticles, particularly QDs. 

Taylor J.R., Fang M.M., Nie S., Probing specific sequences on single DNA molecules with bioconjugated fluorescent nanoparticles, Anal Chem. 2000 72 1979-1986. 

The following methods are based on those cited in the literature or in company instruction manuals for coupling molecules to fluorescent nanoparticles. The coupling of unique proteins or other molecules to QD surfaces may need further optimization of reactant ratios as well as time and temperature to obtain the best conjugates. 

Whenever the commercially available particles do not match the operator s requirements, a variety of possibilities exist in order to modify the particles from company suppliers. Similarly to other doped beads the dyes [92] or quantum dots [107, 108] can be physically entrapped into magnetic beads by swelling or are covalently bound to the surface of the particles. If localization of the dye on the particle surface is desired or if the polarity of dye and/or matrix polymer does not allow the irreversible entrapment of the dye in the bulk polymer, a covalent attachment of the dye is preferable [109, 110]. Even the covalent binding of whole fluorescent nanoparticles to magnetic microparticles is possible, as shown by Kinosita and co-workers who investigated the rotation of molecular motors [111]. 

Fig. 1 Typical organic dye molecules that have been converted to fluorescent nanoparticles. The abbreviation for each dye molecule is also shown in the figure...

Trehin R, Figueiredo JL, Pittet MJ, Weissleder R, Josephson L, Mahmood U (2006) Fluorescent nanoparticle uptake for brain tumor visualization. Neoplasia 8 302-311. 

S.K. Mandal, N. Lequeux, B. Rotenberg, M. Tramier, J. FattaccioU, J. Bibette, andB. Dubertret Encapsulation of Magnetic and Fluorescent Nanoparticles in Emnlsion Droplets. Langmuir 21, 4175 (2005). 

The strong and specific biotin-streptavidin binding was used to assemble biomolecule-functionalized nanoparticles in multilayered structures.67 Application of an electrical field allowed the assembly of multilayer structures by using extremely low concentrations of nanoparticles with minimal nonspecific binding. A microelectrode array was used to facilitate the rapid parallel electrophoretic transport and binding of biotin- and streptavidin-functionalized fluorescent nanoparticles to specific sites. By controlling the current, voltage, and activation time at each nanoparticle adsorption step, the directed assembly of more than 50 layers of nanoparticles was accomplished within an hour. 

Histidine has been shown by Mehra etal. to stabilize fluorescent nanoparticles of ZnS. Nanoparticle synthesis is similar to ZnS-(Cys) methods (see Section 2.1.2). It was noted that the best ratio for nanoparticle formation is 2 1 for histidine to zinc (II). Titrations of sulfide into solutions of the complexed metal and amino acids showed formation of larger particles as the sulfide equivalents increased. This... 

Li, Z.Q., Zhang, Y, and Jiang, S. (2008) Multicolor core/shell-structured upconversion fluorescent nanoparticles. Advanced Materials, 20, 4765-4769. 

In addition to the benefits of MEF from metal nanostructures deposited onto solid supports that are very useful in surface bioassays, MEF can also be observed from individual nanostructures in bioassays carried out in solution. In this regard, fluorophores and metal nanostructures can be assembled in core-shell architecture and can be used as fluorescent nanoparticles as indicators in biological plications such as imaging of cellular activity or single-molecule sensing. 

Irudayaraj et al. have reported the multiplex detection of up to eight different non-fluorescent nanoparticles functionalized with one sequence of DNA [61]. In this approach, a thiolated sequence of DNA was used to functionalize the surface of gold nanoparticles and then non-fluorescent Raman reporters were added to the surface of the nanoparticle to code them with a SERS signal. It was reported that multiplex detection of two, four, and eight differently labeled nanoparticles could be detected in one analysis. However, only one DNA sequence was used in this study to label all the different flavors of nanoparticles and the detection of a specific, target DNA sequence by SERS was not reported. However, it was possible to observe the change in surface plasmon by UV-Vis spectroscopy when two batches of nanoparticles functionalized with complementary sequences were hybridized together. 

Fig. 15.7. Self-assembly of nanoparticles to patterns of binding sites, (a) The transfer DNA is modified with biotin, so that patterns of specific binding sites are created with SMCP. Fluorescent nanoparticles carrying streptavidin self-assemble to these patterns and form superstructures, (b) The formation of superstructures is observed online with TIRF microscopy, (c) The patterns of binding sites were created with different size and incubated with nanoparticles fluorescing at different wavelengths. Also, the scale bar is formed in this way. The pictures are standard deviations of TIRF microscopy image series recorded at 20 Hz...

Other uses of nanostructured chromophores may include fluorescent nanoparticles or nanoparticle-based porous materials that change their light absorption or emission when a toxin is encountered. Some metal oxides and POMs already exhibit such properties. Likewise, electrochemical properties, including induced photocurrents, could be sensitive to encountering a toxin. Clearly, both decontamination and detection are relevant aspects here. Basic research is needed on the design and synthesis of engineered nanostructures whose electronic structures, thermal catalytic, photophysical (emission), and photocatalytic properties are strongly perturbed by the presence or absence of toxic compounds. 

L. Josephson, M. F. Kircher, U. Mahmood, Y. Tang, and R. Weissleder, Near-infrared fluorescent nanoparticles as combined MR/optical imaging probes, Bioconjug. Chem., 13 (2002) 554—560. 

For the purpose of the basic research on electrophoretic transport phenomenon in brain, some basic researches have been carried out using alternatives such as collagen and agarose gels instead of a living mammalian brain [77]. In order to explore the similarity between the porosity of the brain s extracellular compartment and that of the nanoscale polymeric stmcture of the gel, slurry of fluorescent nanoparticles has been applied to monitor the distribution of the nanoparticles within the gel [78]. As seen in Figure 9-39, for example, the nanoparticles of Y203 Eu ... 

Dausend J, Musyanovych A, Dass M, et al. (2008) Uptake mechanism of oppositely charged fluorescent nanoparticles in HeLa cells. Macromol Biosci 8 1135-1143 Ziegler A, Landfester K, Musyanovych A (2009) Synthesis of phosphonate-functionalized polystyrene and poly(methyl methacrylate) particles and their kinetic behavior in miniemulsion polymerization. Colloid Polym Sci. http //dx.doi.Org/10.1007/s00396-009-2087-z Lorenz MR, Kohnle MV, Dass M, et al. (2008) Synthesis of fluorescent polyisoprene nanoparticles and their uptake into various cells. Macromol Biosci 8 711-727... 

Furukawa H, Misu M, Ando K, et al. (2008) Light-controlled on-off switch of a fluorescent nanoparticle. Macromol Rapid Commun 29 547-551... 

Comparable photoswitchable fluorescent nanoparticles with other fluorescent dye/photochrome systems were prepared by Hu et al. [33, 34]. Here, a spiroben-zopyran (BTF6) was co-encapsulated with solvent green 5, disperse yellow 184 [34] and solvent yellow 44 [34]. Due to the spectral overlap of the open-ring form of BTF6 with the emission wavelengths of the respective fluorescent dyes, the fluorescence emission could effectively be quenched and transferred to the encapsulated BTF6. 

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