Quantum dot-mediated biosensing assays for specific nucleic acid detection.

Two new classes of quantum dot (QD)-mediated biosensing methods have been developed to detect specific DNA sequences in a separation-free format. Both methods use 2 target-specific oligonucleotide probes to recognize a specific target. The first method is based on cross-linking of 2 QDs with distinct emission wavelengths caused by probe-target hybridization. The second method uses QDs as both fluorescent tags and nanoscaffolds that capture multiple fluorescently labeled hybridization products, resulting in amplified target signals. The presence of targets is determined according to spatiotemporal coincidence of 2 different wavelength fluorescent signals emitted from the QD/DNA/probe complexes. With a single wavelength-excitation, dual wavelength-emission confocal spectroscopic system, the fluorescent signals can be measured with single-dot/molecule sensitivity. Compared with other nanoparticle-based, separation-free assays, our method shows advantages in simplicity, testing speed, and multiplexed applications.