Probing Biocatalytic Transformations with QDs

CdSe/ZnS QDs were also used to probe DNA hybridization and to follow the biocatalyzed scission of duplex DNA by DNase [190]. For this, the QiSe/ZnS QDs were functionalized with a nucleic add primer (32), and then hybridized with the 

Texas Red-tethered duplex DNA (b) The fluorescence spectra of (spectrum a) the 32-functionalized CdSe/ZnS QDs Spectrum b shows the DNA duplex 32/33 tethered to the 

QDs and the Texas Red chromophore Spectrum c, after treatment with DNase I. (Reproduced with permission from Ref. [190]. Copyright 2005 American Chemical Society). 

In a related study, CdSe/ZnS QDs modified with ssDNA-fluorescent dye conjugates were used to monitor the cleavage of ssDNA by micrococcal nuclease (MNase), with high sensitivity and specificity 191]. For this, the CdSe/ZnS QDs were first functionalized with streptavidin, after which a dye-modified, biotinylated, ssDN A was linked to the particles. In this configuration, the fluorescence of the Q Ds 

Similarly, semiconductor QDs were integrated with proteins, such that the hybrid systems would permit the real-time analysis of catalytic transformations stimulated by the proteins [102, 192-194]. For example, the hydrolytic functions of a series of proteolytic enzymes were followed by the application of QD reporter units, using the FRET process as a readout mechanism. In this case, the QlSe QDs were modified with peptide sequences that were specific for different proteases, where the quencher units were tethered to the peptide termini. Within the QDs/fluorophore-modified hybrid assembly, the fluorescence of the QDs was quenched. Subsequent hydrolytic 

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