Interactions between CdSe/CdS quantum dots and DNA through spectroscopic and electrochemical methods

► The interaction of QDs with DNA has been studied. ► The apparent association constant has been deduced between QDs and DNA. ► The binding force of QDs with dsDNA is stronger than ssDNA. ► The results illuminate that hs-DNA has the high affinity for QDs. The interaction of CdSe/CdS quantum dots (QDs) with Herring sperm-DNA (hs-DNA) has been studied by UV–vis spectroscopy and electrochemical method. Cu(phen)22+/1+ (phen=1, 10-phenanthroline) was used as an indicator for electroactive dsDNA or ssDNA. The apparent association constant has been deduced (4.94×103M−1 and 2.39×102M−1) from the absorption spectral changes of the dsDNA–QDs and ssDNA–QDs. The results of dissociation method suggest that Cu(phen)22+/1+ is more easily dissociated from dsDNA or ssDNA modified gold electrode (dsDNA/Au or dsDNA/Au) in presence of QDs. The dissociation rate constant (k) of Cu(phen)22+/1+ on dsDNA/Au is 4.48 times higher than that in absence of QDs, while k is 2.34 times higher than that in absence of QDs on ssDNA/Au in Tris buffer with low ionic strength (pH 7.0, 0.5mM NaCl). The results illuminate that hs-DNA has high affinity for QDs due to electrostatic force, hydrogen bonds, and van der Waals interactions, and the binding force of QDs with dsDNA is stronger than ssDNA.