A catalytic beacon sensor for uranium with parts-per-trillion sensitivity and millionfold selectivity

doi:10.1073/pnas.0607875104

A catalytic beacon sensor for uranium with parts-per-trillion sensitivity and millionfold selectivity

*Department of Chemistry, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
^†Construction Engineering Research Laboratory, U.S. Army Engineer Research and Development Center, Champaign, IL 61822;
^‡Civil, Construction, and Environmental Engineering Department, Oregon State University, Corvallis, OR 97331; and
^§Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved December 11, 2006 (received for review September 8, 2006)

Abstract

Here, we report a catalytic beacon sensor for uranyl (UO₂ ²⁺) based on an in vitro-selected UO₂ ²⁺-specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3′ quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5′ and 3′ ends, respectively. The presence of UO₂ ²⁺ causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of >1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of ≈230 μM. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium.

Footnotes

^¶To whom correspondence should be addressed at:
Chemical and Life Sciences Laboratories, University of Illinois at Urbana–Champaign, Box 8-6, MC-712, 600 South Mathews Avenue, Urbana, IL 61801.
E-mail: yi-lu{at}uiuc.edu
Author contributions: J.L. and A.K.B. contributed equally to this work; J.L., A.K.B., and Y.L. designed research; J.L., A.K.B., and X.M. performed research; J.L., A.K.B., D.M.C., J.D.I., D.B.W., and Y.L. contributed new reagents/analytic tools; J.L., A.K.B., and Y.L. analyzed data; and J.L. and Y.L. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0607875104/DC1.
Abbreviations:

ICP-AES,

inductively coupled plasma atomic emission spectroscopy;

rA,

ribo-adenosine.