Aqueous synthesis of DNA-functionalized quantum dots for FRET-based DNA detection

Abstract

Forster resonance energy transfer (FRET) based assay is an efficient method for the DNA detection in fast and simple way without complicated step. For practical application, DNA-functionalized CdTe/CdS core/shell quantum dots (QDs), which have long PL lifetime and high PLQY, are needed as an alternative donor instead of the organic dye. Synthesis of QDs is conducted in aqueous solution without ligand exchange and synthesized CdTe/CdS QDs show high PLQY of up to 77%. Furthermore, the PL lifetime of QDs is increased to several hundred nanoseconds with shell growth, which is induced by Type II band structure. DNA-functionalization is achieved directly during the shell growth of QDs. To increase the number of DNA on the surface of QDs and reduce the formation of CdS clusters, the ratio of core solution to shell precursor is optimized to 0.05:1. Since phosphorothioate modified DNA (ptDNA) exists on the surface of QDs, it can be confirmed that non-specific binding is prevented by the steric exclusion of ptDNA. As the result of investigation of target DNA detection using synthesized CdTe/CdS QDs, the target DNA can be detected up to about 13 nM concentration through steady-state PL analysis. In addition, CdTe/CdS QDs can solve the problem of the background signal from the direct excitation of acceptor. Because of its long PL lifetime, direct excitation of the acceptor can be excluded through time-resolved PL analysis. In this study, we synthesized ptDNA-functionalized water-dispersible CdTe/CdS QDs with high PLQY and applied its long PL lifetime for the first time to improve the sensitivity of FRET-based DNA detection.