DNAzyme-based highly sensitive electronic detection of lead via quantum dot-assembled amplification labels.

An electronic DNAzyme sensor for highly sensitive detection of Pb(2+) is demonstrated by coupling the significant signal enhancement of the layer-by-layer (LBL) assembled quantum dots (QDs) with Pb(2+) specific DNAzymes. The presence of Pb(2+) cleaves the DNAzymes and releases the biotin-modified fragments, which further hybridize with the complementary strands immobilized on the gold substrate. The streptavidin-coated, QD LBL assembled nanocomposites were captured on the gold substrate through biotin-streptavidin interactions. Subsequent electrochemical signals of the captured QDs upon acid dissolution provide quantitative information on the concentrations of Pb(2+) with a dynamic range from 1 to 1000 nM. Due to the dramatic signal amplification by the numerous QDs, subnanomolar level (0.6 nM) of Pb(2+) can be detected. The proposed sensor also shows good selectivity against other divalent metal ions and thus holds great potential for the construction of general DNAzyme-based sensing platform for the monitoring of other heavy metal ions.