A small briefcase-sized tool that can detect traces of arsenic in drinking water is being developed as part of a collaborative project by faculty from IIT-M and University of Mexico. While the point-of-need diagnostic tool is aimed at providing a solution to test underground water samples in rural areas before digging a well, researchers said it can be used in wells, lakes and reservoirs in the city as well.
Prof. Balaji Srinivasan, department of electrical engineering, IITM said the tool consists of an optical tip (probe) that looks like a skinny ballpoint pen attached to one end, and the tip will be attached to a spool of fibre which can extend around 200m when drawn out. The pen will be immersible in well water like a fish hook into a lake. A small battery-operated laser-and some optical components- at the other end of the fibre, which has the main control box of the tool, to send light into the fibre and detect the reflected light to measure and display the levels of arsenic in the water. The tool is expected to sense even very low levels of arsenic and give results within a few seconds after the probe is dipped in the water. “Our diagnostic tool will be focussed on detecting very small amounts (below parts per billion levels) of arsenic in water, as needed to determine if the water is safe to drink,” he said. “We are at least a year away from demonstrating a bench top version of the tool,” he added.
The researchers said the heart of the tool is a microbottle optical resonator, a miniature device (as small as a grain of sand) fabricated using an optical fibre into a microbottle form and coating its surface with a chemical sensitive to arsenic. A structured ray of light from a laser light source will be made to travel in the curved surface and undergo an internal reflection. This will result in a very narrow notch or resonance in the spectrum of light that comes back to the box from the detection tip. “This notch in the laser spectrum will be shifted when the contaminant (arsenic) binds to the surface of the microbottle resonator, and the amount of shift in this narrow spectrum will indicate the levels of arsenic in the water,” said Prof Ravinder K Jain, University of Mexico and a visiting faculty at IITM.
The tool can be used to measure dissolved oxygen or any other element by making modifications to the surface of the microbottle resonator, researchers said. A 2017 government data said around 240million people across 21 states in the country were using drinking water contaminated with high levels of arsenic. At present, arsenic levels are measured using electro-chemical sensors, which cannot detect traces or very low levels and are also likely to be contaminated in a field environment, the researchers said.
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