| Abstract
| - A Pb(II)-specific DNAzyme fluorescent sensor has beenmodified with a thiol moiety in order to immobilize it ona Au surface. Self-assembly of the DNAzyme is accomplished by first adsorbing the single-thiolated enzymestrand (HS-17E-Dy) followed by adsorption of mercaptohexanol, which serves to displace any Au−N interactionsand ensure that DNA is bound only through the S-headgroup. The preformed self-assembled monolayer isthen hybridized with the complementary fluorophore-containing substrate strand (17DS-Fl). Upon reaction withPb(II), the substrate strand is cleaved, releasing a fluorescent fragment for detection. Fluorescence intensity maybe correlated with original Pb(II) concentration, and alinear calibration was obtained over nearly four decades: 10 μM ≥ [Pb(II)] ≥ 1 nM. The immobilized DNAzyme isa robust system; it may be regenerated after cleavage,allowing multiple sensing cycles. In addition, drying offully assembled DNAzyme before reaction with Pb(II)does not significantly affect analytical performance. Theseresults demonstrate that, in comparison with solution-based schemes, immobilization of the DNAzyme sensoronto a Au surface lowers the detection limit (from 10 to1 nM), maintains activity and specificity, and allowssensor regeneration and long-term storage. Realization ofPb(II) detection through an immobilized DNAzyme is thefirst important step toward creation of a stand-alone,portable Pb(II) detection device such as those immobilizing DNAzyme recognition motifs in the nanofluidic poresof a microfluidic−nanofluidic hybrid multilayer device.
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