Miniaturized lead sensor based on lead-specific DNAzyme in a nanocapillary interconnected microfluidic device

A miniaturized lead sensor has been developed by combining a lead-specific DNAzyme with a microfabricated device containing a network of microfluidic channels that are fluidically coupled via a nanocapillary array interconnect. A DNAzyme construct, selective for cleavage in the presence of Pb²⁺ and derivatized with fluorophore (quencher) at the 5́ (3́) end of the substrate and enzyme strands, respectively, forms a molecular beacon that is used as the recognition element. The nanocapillary array membrane interconnect is used to manipulate fluid flows and deliver the small-volume sample to the beacon in a spatially confined detection window where the DNAzyme is interrogated using laser-induced fluorescence detection. A transformed log plot of the fluorescent signal exhibits a linear response (r² = 0.982) over a Pb²⁺ concentration range of 0.1-100 μM, and a detection limit of 11 nM. The sensor has been applied to the determination of Pb ²⁺ in an electroplating sludge reference material, the result agreeing with the certified value within 4.9%. Quantitative measurement of Pb²⁺ in this complex sample demonstrates the selectivity of this sensor scheme and points favorably to the application of such technologies to analysis of environmental samples. The unique combination of a DNAzyme with a microfluidic-nanofluidic hybrid device makes it possible to change the DNAzyme to select for other compounds of interest, and to incorporate multiple sensing systems within a single device for greater flexibility. This work represents the initial steps toward creation of a robust field sensor for lead in groundwater or drinking water.