Stress-check: Light beamed through spit

Shining ultra-fast laser beams through saliva can detect stress levels with a precision that could be superior to current methods of using blood or less reliable biochemical saliva tests, if commercialised, reports Reshma Patil.

About one year ago, a medical physicist from Manipal, Karnataka, travelled to molecular scientist Deepak Mathur’s laboratory in South Mumbai, clutching an icebox. The box was full of spit from many mouths in Manipal.

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In experiments that followed, infrared laser shot through the saliva turned the droplet into a plasma that looks like a circle of green, red and blue colours as hot as the sun. If a laser beam accidentally touched your finger, it would pierce a hole.

That’s how, in one of Asia’s top laser laboratories at the Tata Institute of Fundamental Research, (TIFR) Mathur and C Santosh, head of laser spectroscopy at the Manipal Life Sciences Centre, have proposed an international first. Shining ultra-fast laser beams through saliva can detect stress levels with a precision that they claim could be superior to current methods of using blood or less reliable biochemical saliva tests, if commercialised.

Saliva contains a protein that is a direct measure of physiological and psychological stress. As stress levels contribute to lifestyle diseases — software giant Infosys even operates a hotline and stress audits for staff — using saliva as a non-invasive ‘stress marker’ is a subject of competitive global research with implications for India.

How it works

From a swab of saliva, a protein that identifies stress level is isolated.

Ultra-fast light is shot through water and its frequency spectrum recorded.

When the protein is added, the light spectrum narrows.

Simply put, the narrower the light, higher the stress level.

“Our concept is workable if a clever company pursues it to design a hospital instrument,” said Mathur, who described results in the international Journal of Biomedical Optics last March. “We are the first to propose using intense-laser technology to detect stress from saliva. But at the research stage, it’s expensive.”

Researchers could team with TIFR to study stress levels of Indian call-centre staff or business leaders.

“It’s a wonderful observation,’’ said Santosh. “Saliva is hardly used as a stress indicator today since the signature between stress and saliva is not clearly established. Our technology could immediately quantify and correlate stress with saliva.”

Mathur studies light and matter interactions in his atomic and molecular sciences department, where experiments help explain how stars form, to how shockwaves would theoretically be generated in a nuclear bomb test. Often, the laser explodes dust particles, generating energy that cracks mirrors.

When they shot light through saliva, the light’s spectrum became narrower instead of broader as expected, thus indicating the presence of the stress marking protein. The narrower the spectrum, the higher is the concentration of stress. Doctors could use data from this technique to analyse stress levels.

They are setting up a lab at Manipal for clinical trials with samples from healthy volunteers and smokers to cancer patients. “Hospitals that use saliva diagnosis rely on equipment that profiles all chemical constituents of saliva, leading to high chances of error,” said Mathur. “Unlike laser technology, it also requires biochemicals added to samples.”

Spitting is, of course, discouraged at TIFR.