Spectrophotometric detection of lead(II) ion using unimolecular peroxidase-like deoxyribozyme

Deoxyribonucleic acid (DNA) can form G-quadruplexes in the presence of certain metal ions. These play a functional role in a variety of biological process. A DNA 17-mer (PW17) was previously reported to bind hemin in the presence of excess potassium ion. The resulting stabilized G-quadruplex-hemin complex exhibits peroxidase-like activity. However, this activity is lost in the presence of one equivalent of Pb2+ ion. We exploit this property in a method for spectrophotometric detection of Pb2+. Inhibition by Pb2+ ion is reflected by a change in the Soret band of hemin and a sharp reduction in the catalytic activity towards hydrogen peroxide-mediated chromogenic oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate. The new method enables Pb2+ to be detected in the concentration range from 0.05 to 1.2 mu M, with a detection limit of 27 nM. The assay shows high selectivity over other metal ions. It was successfully used to determine Pb2+ in water samples.