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An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion ([Pb.sup.2+]) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to [Pb.sup.2+]and the use of DNA--Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for [Pb.sup.2+] is immobilized onto an Au electrode surface via a thiol--Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA--Au biobar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru[(N[H.sub.3]).sub.6.sup.3+], which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of [Pb.sup.2+] to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru[(N[H.sub.3]).sub.6.sup.3+] from the Au electrode surface. The release of Ru[(N[H.sub.3]).sub.6.sup.3+] results in lower electrochemical signal of Ru[(N[H.sub.3]).sub.6.sup.3+] confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru[(N[H.sub.3]).sub.6.sup.3+] provides quantitative measures of the concentrations of [Pb.sup.2+], with a linear calibration ranging from 5 nM to 0.1 [micro]M. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru[(N[H.sub.3]).sub.6.sup.3+], the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of [Pb.sup.2+] at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for [Pb.sup.2+]. Although this DNAzyme sensor is demonstrated for the detection of [Pb.sup.2+], it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

Submicro- and nanometer-sized glass double-barrel pipets have been fabricated by a laser puller with new pulling programs and have been used to support submicro- and nanometer dual liquid/liquid interfaces. The smallest pipet that can be made by this approach is ~20 nm in radius. These pipets have been characterized by cyclic voltammetry and scanning electron microscopy. Generation/collection mode of charge-transfer reaction is demonstrated at the submicro- and nanometer dual-liquid/ liquid interfaces. The dependence of collection efficiency upon geometric parameters of the pipets has been discussed. Among the micro-, submicro-, and nanopipets, we have found that the submicro-double-barrel pipets have higher collection efficiencies than that of others and are also very close to the values predicted by the theory. Therefore, in terms of G/C mode applications, the optimal size of double-barrel pipets should be in submicrometer scale. As one of the examples of special application, we have also demonstrated that in the case of no supporting electrolyte, only the nanometer double-barrel pipets can provide reasonably good G/C results.