LETTERS Single-quantum-dot-based DNA nanosensor

Rapid and highly sensitive detection of DNA is criticalin diagnosing genetic diseases. Conventional approachesoften 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 kinetics1,2. Here, we report 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)3–5 linked to DNA probes to capture DNA targets. The target strandbinds to a dye-labelled 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 nanosensor