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Quantum-Dot-Based DNA Nanosensors
Rapid and highly sensitive detection of DNA is critical in diagnosing genetic diseases. Conventional approaches often rely on cumbersome, semi-quantitative amplification of target DNA to improve detection sensitivity. In addition, most DNA detection systems (microarrays, for example), regardless of their need for target amplification, require separation of unhybridized DNA strands from hybridized stands immobilized on a solid substrate, and are thereby complicated by solution–surface binding kinetics. Professor Tza-Huei Wang’s lab has reported an ultrasensitive nanosensor based on fluorescence resonance energy transfer (FRET) capable of detecting low concentrations of DNA in a separation-free format. This system uses quantum dots (QDs) linked to DNA probes to capture DNA targets (Figure 1). The target strand binds to a dye-labeled reporter strand thus forming a FRET donor–acceptor ensemble. The QD also functions as a concentrator that amplifies the target signal by confining several targets in a nanoscale domain. Unbound nanosensors produce near-zero background fluorescence, but on binding to even a small amount of target DNA (50 copies or less) they generate a very distinct FRET signal (Figure 2). A nanosensor-based oligonucleotide ligation assay has been demonstrated to successfully detect a point mutation typical of some ovarian tumors in clinical samples.
Figure 1: QD nanosensors for detection of sequence-specific DNA. The presence of a specific DNA target leads to formation of a nanocomplex comprising a QD, DNA probes, and targets, which causes FRET between a QD and a fluorophore (Cy5) labeled on a DNA probe.
Figure 2: Single-particle fluorescence imaging. In the presence of targets, fluorescent signals are detected for both the donor (605QD) and the acceptor (Cy5), while only donor signals are detected in the absence of targets.
References
C. Y. Zhang, H. C. Yeh, M. Kuroki, T. H. Wang, " Single-Quantum-Dot-Based DNA Nanosensor," Nature Materials 4(11):826-831, 2005
H. C. Yeh, Y. P. Ho, I. M. Shih, T. H. Wang, " Homogeneous point mutation detection by quantum dot-mediated two-color fluorescence coincidence analysis," Nucleic Acids Research 34(5):e35, 2006
Y. P. Ho, M. C. Kung, S. Yang, T. H. Wang, " Multiplexed Hybridization Detection with Multicolor Colocalization of Quantum Dot Nanoprobes," Nano Letters 5(9): 1693-1697, 2005