A highly sensitive and selective optical sensor for Pb2+ by using conjugated polymers and label-free oligonucleotides

The detection of Pb2+ with DNA-based biosensor is usually susceptible to severe interference from Hg2+ because of the T-Hg2+-T interaction between Hg2+ and T residues. In this study, we developed a rapid, sensitive, selective and label-free sensor for the detection of Pb2+ in the presence of Hg2+ based on the Pb2+-induced G-quadruplex formation with cationic water-soluble conjugated polymer (PMNT) as a "polymeric stain" to transduce optical signal. We selected a specific sequence oligonucleotide, TBAA (5'-GGAAGGTGTGGAAGG-3'), which can form a G-quadruplex structure upon the addition of Pb2+. This strategy provided a promising alternative to Pb2+ determination in the presence of Hg2+ instead of the universal masking agents of Hg2+ (such as CN-, SCN-). Based on this observation, a simple "mix-and-detect" optical sensor for the detection of Pb2+ was proposed due to the distinguishable optical properties of PMNT-ssDNA and PMNT-(G-quadruplex) complexes. By this method, we could identify micromolar Pb2+ concentrations within 5 min even with the naked eye. Furthermore, the detection limit was improved to the nanomolar range by the fluorometric method. We also successfully utilized this biosensor for the determination of Pb2+ in tap water samples. (C) 2012 Elsevier B.V. All rights reserved.