By soldering two additional light sensors inside the CD player, and then using software, the researchers were able to control how the device "played" a disk. The substance to be analyzed (in this case, the team was trying to detect traces of three different pesticides in various samples) was then placed on a normal compact disc, and inserted into the machine.
While the first light sensor identified where the sample was on the disc, using black marks on the edge of the disc, the second analyzed the sample itself, measuring the amount of laser light that was able to pass through the disk. Normally, discs reflect around 30 percent of the laser beam onto the reading head, while the rest passes through.
The sample, half a millimeter in size, was treated to produce dye or silver that was inversely proportional to the amount of pesticide in the sample. Using the modded CD player, they could detect pesticide levels as low as 0.02 micrograms per liter just by seeing how much laser light passed through the disc to the second sensor.
While it may not be as accurate as genuine lab sensors, which can cost between $42,000 and $85,000, the hacked CD player is accurate enough for many laboratory tasks &mdash some experts think the cheap and cheerful device would work wonders in developing countries, helping the fight against malaria, for instance. And the shorter wavelength lasers of Blu-ray and HD DVD technology will make the process even easier. [New Scientist]