One of the Most Important Tools in Science Now Fits Inside Your Phone

A spectrometer that fits in your mobile devices could let you scan yourself for skin cancer.

Illustration by Mary O'Reilly

We use them to spy on exoplanets, diagnose skin-cancer, and ID the makeup of unknown chemicals. They're on NASA spacecraft flying around Saturn's moons right now. Yes, right alongside the microscope, the optical spectrometer—an instrument that breaks down the light that something reflects or emits, telling you what its made of—is one of the most ubiquitous tools in all of science. Today, Jie Bao, a physicist at Tsinghua University in Beijing, China, has just discovered a fascinating way to make them smaller, lighter, and less expensive than we ever thought possible.

By using tiny amounts of strange, light-sensitive inks, Bao and his colleague Moungi Bawendi—a chemist at MIT—have designed a working spectrometer that's small enough to fit on your smartphone. Because of the tool's simple design and its need for only an incredibly small amount of the inks, Bao says, his spectrometer only requires a few dollars worth of materials to make. They report the research today in the journal Nature.

"THAT'S WHAT I'M REALLY HOPING FOR, SEEING THEM IN CELLPHONES IN THE VERY NEAR FUTURE."

"Of course we still have a lot of room for improvement. But performance-wise, even at this preliminary stage, our spectrometer works very close to what's currently being sold in the market," Bao says. "I think that's one of the most attractive results of our research: [This spectrometer] is already so close to a real product."

Printable Detectors

The way spectrometers work goes back to the 17th century, when Issac Newton showed that a prism could break up white light into distinct bars (technically wavelengths) of different colored light. Depending on the source of the light—say, a candle or the sun—that rainbow spectrum would change. Today, we know this happens because the atomic or molecular makeup of everything that either gives off or reflects light leaves an indelible fingerprint. And if you understand which materials leave which fingerprints, you can use light alone to find out what something is made of.

Bao says most modern spectrometers are made in more or less the same way. They diffract incoming light, then push it through a mechanically movable slit to see which exactly which wavelengths of light fit through which slits. This setup, because it involves complex moving pieces, is a total pain to shrink down in size. It's expensive, too, because accurate spectrometers require high-precision components and delicate alignment.

Jie Bao

But Bao's spectrometer works in a much simpler way. As if making micro-sized stained glass windows, Bao prints a tiny grid of 195 different-colored liquid inks directly onto a flat sensor. (That sensor, called a CCD sensor, is what your phone's camera uses to pick up light.) Each of the 195 windows is made of a material called colloidal quantum dots, and each "absorbs certain wavelengths of light, and lets others go," says Bao. When light hits each window and travels through, the underlying sensor records how the light changed. Later, a computer can compare the data from all of the windows and reconstruct what wavelengths made up the original light.

Cellphone Spectrometers

Right now, Bao's spectrometer is about the size of a quarter, and he says the underlying CCD sensors he uses can be bought online for less than a dollar a pop. Because he's using just a tiny drop of each of the colloidal quantum dot inks (which have only recently been developed) the cost all 195 drops is only on the order of a few dollars.

"THE PEOPLE WHO ARE PLANNING SPACE MISSIONS ARE WEIGHING EVERY GRAM."

Because spectrometers are so widely used in science, Bao sees a rainbow of possible uses for his new device. For one, he says, his spectrometers could be easily integrated into commercial smartwatches and phones, allowing everyday people to do things like self-identify skin cancer. "That's what I'm really hoping for, seeing them in cellphones in the very near future," he says.

And because spectrometers are so widely used on exploratory spacecraft, Bao sees an easier and far cheaper way to deck out the next generation of space explorers. "The people who are planning space missions are pretty much weighing every gram, and so this would be a very easy way to lose weight."

ORIGINAL: Popular Mechanics

By William Herkewitz

Jul 1, 2015