Two colour quantum dots can rapidly detect DNA with a high sensitivity, according to US chemists.
 
Chunyang Zhang and Lawrence Johnson of the City University of New York have developed a robust method to detect very small amounts of DNA using quantum dots that fluoresce at two different frequencies.

A probe is used to recognise and bind to specific DNA. This DNA-probe hybrid attaches to the surface of one type of quantum dot, and another type attaches to the free end of the hybrid. A positive result is given only when both fluorescing dots are detected.

The polymerase chain reaction is routinely used to detect tiny amounts of DNA, but contamination can cause false positive results. Single molecule techniques that detect fluorescent markers also allow sensitive detection, and using two signals means that the likelihood of a false positive result is low. 

Zhang and Johnson's test can also be used over a range of temperatures. This is another improvement on existing methods, said Johnson.

Zhang and Johnson said that their technique will be developed and applied to DNA, RNA and protein analyses such as testing for hereditary diseases, paternity testing and for forensic use.

Susan Batten