Quantum dots bar-code DNA

17 Jun 2002

Microbead bar-codes make light work of screening biological molecules.

As today's research into genomics and proteomics generates increasing amounts of biological sequence data, researchers are clamoring for technologies that can sift through massive numbers of proteins. Scientists from the US-based University of Indiana have developed a "biological bar-coder", that they believe holds the answer, (Nature Biotechnology 19 631-635).

Mingyong Han and colleagues embedded light-emitting nanocrystals known, as quantum dots, into tiny polymer beads. By tagging their microbeads onto strands of DNA, the researchers created a "chemical lab" that detects and analyzes DNA molecules.

The scientists fabricated the quantum dots from zinc sulphide coated cadmium selenide crystals, and believe that the quantum dots make ideal fluorophores. "This new class of luminescent labels is 20 times as bright and three times as [sharp] as organic fluorescent dyes," said Han. By changing the size of the crystal, the researchers can also vary the color it emits.

Claiming that the beads can track and identify DNA with nearly 100% accuracy, the scientists estimate that a realistic system could use just five colors with six intensity levels to identify as many as 40 000 recognizable codes. "Theoretically, up to one million nucleic acid or protein sequences could be coded," added Han.

Han and colleagues now aim to advance applications such as high-throughput screening and medical diagnostics, but realize that a "library" with individually coded beads to match single proteins must be developed first. However, once achieved it could only be a matter of time until bar-coders herald ultrasensitive systems that detect the early stages of disease.