Femtomolar electrochemical detection of DNA targets using metal sulfide nanoparticles

A new electrochemical DNA sensor providing detection capabilities down to 100 attomol of target DNA has been developed. The method applies CdS, ZnS, and PbS nanoparticles conjugated with short DNA sequences which are immobilized via hybridization with complementary sequences on a gold surface. When the DNA target is added, it can be identified by ousting the existing hybridization between one of the DNA-nanoparticle conjugates and the surface DNA. The nanoparticles remaining at the surface are detected by stripping voltammetry. The setup is constructed to give a signal-off response with a build-in control signal as only one of two different metal sulfide signaling probes on the surface is removed by hybridization with the DNA target. The competition assay is, in principle, label-free since no labels are required for detection after addition of DNA target. The dissociation of PbS nanoparticles from the surface after addition of the DNA target has been imaged by fluid phase AFM.