Researchers at IIT-Madras developed a point-of-need diagnostic tool for testing underground water samples in rural areas.

As explained, the tool can be used for up to 200 meters underwater in lakes and other water bodies as well.

The fundamental element of the tool is a micro bottle optical resonator, a device as small as a grain of sand, fabricated using optical fiber, and whose surface is coated with a chemical sensitive to arsenic.

The tool consists of an optical tip (probe), as small as a skinny ballpoint pen, with the tip attached to a spool of fiber that can extend around 200m when drawn out.

This battery-operated device detects the reflected light, measuring the levels of arsenic in water.

The pen will be immersible in water.

Prof Ravinder K Jain, University of Mexico, explained how the notch in the laser spectrum will shift when the contaminant (arsenic) binds to the surface of the micro bottle resonator, and this shift will indicate the levels of arsenic in the water.

This tool can sense even very low levels (below parts per billion levels) of arsenic within a few seconds after the probe is dipped to determine the safety of drinking water..

In 2017, around 240 million people across  the country were found to have arsenic levels higher than normal, even today, levels are measured using electro-chemical sensors that are not very efficient at detecting further lower levels.