Tech + Engineering

10
Mar

Chemists Hack Blu-ray Players to Test for Salmonella and Parasites

The Blu-ray player under your TV isn’t just for playing movies—it can also test your food and water to see if it’s safe.

A team of researchers in Spain have taken off-the-shelf Blu-ray players and discs and, with a little hacking, turned them into cheap medical screening devices to detect dangerous bacteria and parasites. The disc acts as the platform for the sample, and the laser scans the samples. The team reports that it’s just as accurate as conventional lab equipment at a fraction of the cost and size, meaning health workers could take them into remote areas to test water supplies and monitor the environment.

Blu-ray player | Diego Correa | Flickr-CC
With a little modification, Blu-ray players can be a cheap and effective clinical testing device.

Normally, a Blu-ray player works by using its 405-nm laser to read the microscopic pits that make up the digital ones and zeros of the disc’s data. But the team installed a custom data board to read out an analog signal that measures the reflectivity of the disc.

The discs were prepared by attaching bits of DNA or pieces of protein, known as probes, to the surface of the disc and recorded which bit was placed where on the disc. The probes work by snagging certain complementary strands or compounds from the test solution. To test a sample, they ran the solution containing the pathogen’s DNA or microcystin, a toxic produced by certain bacteria, over the data side of a Blu-ray disc. When they washed off the excess solution, the DNA or toxin remains stuck to the appropriate probes. The researchers then popped the disc in the drive and spun it up. The laser scans the disc, building a high-resolution image. The team then analyzes the image to see which probes attracted which DNA strand or compound.

So far, they’ve tested the method with two types of bacteria: Salmonella typhimuium, and an intestinal parasite known as Cronobacter sakazakii. It also worked with microcystins, a biotoxin created by cyanobacteria that can infect drinking water and cause gastrointestinal unpleasantness and allergic reactions.

Perhaps surprisingly, using optical discs as life science laboratory instruments isn’t new. Here’s Sergi Morais, one of the project’s team members, being interviewed by Matthew Peach of Optics.org:

“Our team has been working with this type of technology for 10 years. We started working with regular CDs then DVDs. Then we realized that Blu-ray was even more sensitive than the previous formats.”

There are a couple reasons why the Blu-ray format, which was introduced to accommodate HD video, works better as a medical screening device.

First, the coating on Blu-ray discs is extremely hydrophobic, which means it repels water. So when researchers apply sample drops to the surface, they tend to stay bunched up in a sphere instead of spreading out across the surface. That means they can fit more samples onto a single disc, and it also improves the quality of the laser’s data. Second, the laws of physics allow Blu-ray’s blue lasers to be focused to a smaller area than the red lasers in DVD players; this is why we can cram more data onto a Blu-ray disc, and it also means the researchers can get clearer images of the sample drops. Together, these features make Blu-ray players several times more accurate than DVD players for this kind of testing.