Nuclease-resistant DNA aptamer on gold nanoparticles for the simultaneous detection of Pb2+ and Hg2+ in human serum

There has been great progress in the development of functional DNA-based sensors for the detection of metal ions. However, many functional DNAs are vulnerable to hydrolysis by nucleases in human blood. In addition, the detection methods that are based on DNA often exhibit interference due to the high blood concentrations of other ions, such as K+ and Na+ Therefore, we selected highly Pb2+-specific DNA-aptamer sequences based on CD spectroscopy of 4 G-rich DNA sequences and Hg-specific T-rich DNA sequences and immobilized them on gold nanoparticles for the simultaneous detection of Pb2+ and Hg2+ in human serum. We used gold nanoparticles because these have a superior fluorescence-quenching efficiency over a broad range of wavelengths compared with other organic quenchers. In addition, gold nanoparticles have a stabilizing effect on the immobilized DNA, which makes it more resistant to degradation by nucleases than free DNA. As a result, even in the presence of DNase, we were able to simultaneously detect Pb2+ and Hg2+ in serum at concentrations as low as 128 pM and 121 pM, respectively, within 10 min. These detection limits for Pb2+ and Hg2+ were 39-fold and 26.4-fold lower, respectively, than the detection limits that were obtained using free DNAs. Given the multi-color-fluorescence quenching capability of the gold nanoparticles and the possibility of developing functional nucleic acids for the detection of other metal ions, this study extends the application of oligonucleotides to a point-of-care detection system for the detection of multiple harmful metal ions in body fluids. (C) 2012 Elsevier B.V. All rights reserved.