DNA-based biosensor detects lead ions in real time

Researchers at the University of Illinois (UI), Urbana-Champaign, have developed a new type of sensor for detecting lead ions on-site in real time. The sensor, which employs DNA molecules that selectively bind to lead, is said to be both simpler to use and less expensive than current chemical tests for lead contamination.

According to Yi Lu, the UI chemist who developed the analytical procedure, the new devices are the first catalytic DNA-based biosensors for metal ions. They are attractive, he notes, because they combine the high metal-ion selectivity of catalytic DNA with the high sensitivity of fluorescence detection. DNA as a binding medium has an advantage of being stable, cost-effective and easily adaptable to optical fiber and chip technology, the UI researcher adds. The new device, he says, is an ideal candidate for real-time, remote sensing of lead in applications such as environmental monitoring, clinical toxicology and industrial process monitoring.

To search for the unique sequence of DNA that could distinguish lead from other metal ions, Lu and graduate student Jing Li used in-vitro selection. Their selection process was capable of sampling a very large pool of DNA sequences (up to 1000 trillion molecules), amplifying the desired sequences by the polymerase chain reaction and introducing mutations to improve performance. Using this procedure, Lu and Li found several DNA sequences that were especially responsive to the presence of lead ions. To enhance the sensitivity of the sensor, the researchers attached a fluorescent tag to a specific DNA sequence.

While most DNA is double stranded, the catalytic DNA Lu and Li selected has a single strand that can wrap around like a protein. In that single strand, the researchers fashion a specific binding site -- a kind of pocket that can only accommodate the metal ion of choice.

"The principles demonstrated in this work can also be used to obtain DNA biosensors for other metal ions that are toxic (such as mercury and cadmium) or beneficial (such as calcium and potassium) to humans," Lu said in a recent UI press release. "At the same time, we can offer insight into both the sequence and structure of DNA that is responsible for the metal specificity."

Lu and Li described their catalytic DNA sensor in the Oct. 25 issue of the Journal of the American Chemical Society. Funding was provided by the National Institutes of Health. The researchers have applied for a patent.

For more information, contact James E. Kloeppel, University of Illinois, at 217-244-1073, or kloeppel@uiuc.edu.

Edited by Gordon Graff
Managing Editor, Laboratory Network.com
ggraff@vertical.net