Sensitive single-color fluorescence "off-on" switch system for dsDNA detection based on quantum dots-ruthenium assembling dyads

Due to the high importance of detecting DNA with both fast speed and high sensitivity, we proposed a new dsDNA detection method relying on a novel single-color fluorescence "off-on" switch system. Water-soluble glutathione capped CdTe QDs (emission at 605nm) was prepared for taking advantage of the readily tunable emission property of QDs. Initially, QDs was completely quenched by the Ru(phen)₂(dppz)²⁺, as the spontaneous formation of QDs-Ru assembling dyads. Then, in the case of the addition of dsDNA, the Ru(phen)₂(dppz)²⁺ was removed away from the CdTe QDs, producing free CdTe QDs and the Ru-dsDNA complex. Both of them could be excited at the same wavelength and emit overlaid fluorescence. This single-color fluorescence "off-on" signal was sensitive to the concentration of dsDNA. Native dsDNA with the concentration of 10pg/mL could be detected when 0.5nM CdTe QDs was used, and ssDNA, RNA or BSA had no interference on it. With this system, the dsDNA samples of hepatitis B virus (HBV) patients were tested. The results were in good agreement with those detected by fluorescence quantitative PCR (P>0.05), and for those samples with very low DNA concentrations, this system could provide more accurate results, demonstrating the possible clinical applicability of this "off-on" switch system. For this system, chemical conjugation or labeling of probes is not required, and unmodified native DNA targets could be detected in less than half an hour. Therefore, a simple, fast, sensitive, low cost, highly selective and practically applicable detection system for dsDNA has been described.