Highly Selective DNA-Based Sensor for Lead(II) and Mercury(II) Ions

Abstract

We have developed a technique for the highly selective and sensitive detection of Pb(2+) and Hg(2+) using a thrombin-binding aptamer (TBA) probe labeled with the donor carboxyfluorescein (FAM) and the quencher 4-([4-(dimethylamino)phenyl]azo)benzoic acid (DABCYL) at its 5' and 3' termini, respectively. The TBA has a random coil structure that changes into a G-quartet structure and a hairpin-like structure upon binding Pb(2+) and Hg(2+) ions, respectively. As a result, the fluorescence decreases through fluorescence resonance energy transfer (FRET) between the fluorophore and quencher. These changes in fluorescence intensity allow the selective detection of Pb(2+) and Hg(2+) ions at concentrations as low as 300 pM and 5.0 nM using this TBA probe in the presence of phytic acid and a random DNA/NaCN mixture, respectively. The linear correlation existed between the fluorescence intensity and the concentration of Pb(2+) and Hg(2+) over the range of 0.5-30 nM (R(2) = 0.98) and 10-200 nM (R(2) = 0.98), respectively. To the best of our knowledge, this is the first example of a single DNA-based sensor that allows the detection of both Hg(2+) and Pb(2+) ions. This simple and cost-effective probe was also applied to separately determine Pb(2+) in soil samples and spiked Hg(2+) in pond samples.

Potential uses of G-quadruplex-forming aptamers

“…The issue of the high sensitivity of the TBA sequence to various cations is raised in research focused on the detection of K + Cai et al 2010), Pb 2+ and Hg 2+ (Liu et al 2009;Li et al 2010) using various physical methods. TBA sequences were also incorporated in nanopores formed by α-hemolysin (α HL) in bilayer lipid membrane; the addition of cations, especially K + , resulted in the folding of TBA into quadruplexes and reduced the current flowing through the nanopore (Shim et al 2009).…”

A sensitive fluorescence anisotropy method for detection of lead (II) ion by a G-quadruplex-inducible DNA aptamer

“…In addition, some of these G-quadruplexes, with hemin as a co-factor, exhibit superior peroxidase-like activity and can effectively catalyze the H 2 O 2 -mediated oxidation of 2,2 -azino-Bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) or luminol [44]. Based on Pb 2+ -induced allosteric G-quadruplex oligonucleotides and the effect of Pb 2+ on peroxidase-mimetic activity, highly sensitive, and selective Pb 2+ -sensors have utilized these properties to generate fluorescent [45][46][47][48][49], colorimetric [50,51], luminescent [52], electrochemical [53][54][55], and resonance scattering signals [56,57]. Compared with Pb 2+ -dependent RNA-cleavage DNAzymes, G-quadruplexes have a relatively low cost of synthesis and high stability.…”

Aptamer-based and DNAzyme-linked colorimetric detection of cancer cells

“…Aptamer-based biosensors not only exhibit desirable selectivity, specificity and affinity, but also show distinguished advantages (Famulok et al, 2000;Xiao et al, 2005), allowing them to be a senior method for biosensing and diagnostic applications. In the late decade, aptamers have been broadly used in the fabrication of biosensor for the detection of ions (Liu et al, 2009), micromolecules (Baker et al, 2006) and proteins (Degefa and Kwak, 2008). Recently, Herr et al (2006) made use of aptamer to target cancer cells.…”