Practical, highly sensitive, and regenerable evanescent-wave biosensor for detection of Hg(2+) and Pb(2+) in water.

A "turn-on" evanescent-wave fiber biosensor based on functional nucleic acids was developed for on-site detection of Hg(2+) and Pb(2+) in environmental water samples. A two-step strategy was conducted to take advantage of the rapid binding of T-T mismatches with Hg(2+) and the cleavage of a substrate by 8-17 DNAzyme with Pb(2+) in solution, as well as sensitive DNA detection on a liquid-solid interface based on evanescent wave. The biosensor demonstrated high sensitivity (with a detection limit of 22 pM for Hg(2+) and 20 nM for Pb(2+)) and selectivity without any signal amplification, rapid detection (within 13 min per test), low cost (10-20 Chinese yuan per sample), and multiple-cycle regeneration (at least 18 times). The method was also successfully applied on Hg(2+) and Pb(2+) detection in real environmental water samples.