DNA leads the way in environmental sensor

Researchers from the University of Illinois have developed a unique sensor to detect lead, a common environmental contaminant responsible for a host of maladies.

The sensor, which employs DNA, is said to be a simple and inexpensive tool that permits real-time, on-site detection of lead ions.

DNA is being used in the sensor because of its stability, cost-benefits and adaptability to optical fibre and chip technology.

‘This represents a new class of simple and environmentally safe sensors and is the first example of a catalytic DNA-based biosensor for metal ions,’ said Yi Lu, a professor of chemistry at the University of Illinois.

To search for the unique sequence of DNA that could distinguish lead from other metal ions, Lu and graduate student Jing Li used a method called in vitro selection.

The selection process is capable of sampling up to 1000 trillion molecules amplifying the desired sequences by a polymerase chain reaction and introducing mutations to improve performance.

Using in vitro selection, Lu and Li found several DNA sequences that were sensitive 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 which acts like a 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,’ said Lu. ‘At the same time, we can offer insight into both the sequence and structure of DNA that is responsible for the metal specificity.’