Listening For Lead

MP3s may soon outsell compact discs, but the CD drive has gained a new job: reading lead levels. Researchers have created a CD-based assay as an inexpensive and rapid field test for analyzing lead in drinking water and other environmental samples (Anal. Chem., DOI: 10.1021/ac103177w).

Lead is a neurotoxic metal. Existing techniques, such as reversed-phase high-pressure liquid chromatography, can measure lead concentrations at very low levels but they demand sophisticated equipment and laborious sample preparation. Simple lead detection kits are available, says Hua-Zhong Yu of Simon Fraser University in Burnaby, British Columbia, but they can give incorrect readings when other metals are present.

So Yu's team, along with colleagues at the Northwest Institute of Plateau Biology in China, designed a more-selective simple lead test. The scientists immobilized two types of biomolecules on a CD: DNA-cutting enzymes that only lead can activate, and gold-nanoparticle-tagged DNA strands made visible with a silver stain. They then pipetted a water sample onto the CD and popped it into a CD drive.

The CD also had audio files stored on it. If the water sample lacked lead, the enzymes remained inactive, and the silver-stained nanoparticles blocked access to the audio files. As lead amounts increased, the activated enzymes removed more and more the nanoparticle-tagged DNA. The CD drive's laser gradually measured less signal from the nanoparticles and eventually hit the files, making them audible. The method could detect as little as 10 nM of lead, which makes it adequate for environmental analyses.

Because the silver stain is visible to the naked eye, Yu says the assay can give a qualitative result without even using the CD drive: After sample treatment, a yes/no answer about lead can come from a quick glance to see whether the stain is still there.