Topic: DIY lab scanner made from standard CD drive

[Nemesis]

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Fixing two additional light sensors to a normal CD or DVD drive can transform it into a highly accurate scanner for chemical or medical tests, Spanish researchers have shown. The team has developed a modified CD drive that detected tiny quantities of pesticide in samples placed on top of an ordinary compact disk.

Maquieira and colleagues soldered two extra light sensors inside a CD player, and used software to control the way the device "plays" a disk.

The first sensor identifies the sector of a disk containing a sample using black marks on the edge of the disk. The second analyses the sample itself, measuring the amount of laser light that is able to pass through the disk. The off-the-shelf disks used normally reflect around 30% of the laser beam onto the reading head, with the rest passing through.

In experiments, the researchers used their modified drive to detect traces of three different pesticides. A sample – half a millimetre across on a disk – was treated normally, using a set of reactions that produce an amount of dye or silver that is inversely proportional to the amount of pesticide in the sample.

The amount of laser light that passed through the disk to the second sensor indicated the levels of dye or silver. The modified drive was thus able to detect levels of pesticide as low as 0.02 micrograms per litre.

Although the hacked device lags behind the performance of specialised machines, it is accurate enough for many lab tasks, the team says.