A $20 sensor invented by two University of Waterloo researchers could save lives by letting ordinary people detect contaminated drinking water using their cell phone.

“No one should ever have to become sick or die from contaminated food or water,” says Simarjeet Saini, a professor in the Department of Electrical and Computer Engineering“This sensor could save thousands of lives.”    

One billion people lack access to clean drinking water

Water safety is a major global concern, especially in countries such as India and China where an estimated one billion people lack access to clean drinking water. Water safety testing currently requires expensive, specialized equipment not accessible to the average citizen.

Drinking waterSaini, who is also with the University's Waterloo Institute for Nanotechnology (WIN), worked with post-doctoral research fellow Mohammadreza Khorasaninejad to develop a nano-photonic chip called a Surface Plasmon Array Sensor (SPiAS).  Nanotechnology involves developing devices that are measured in nanometers. A human hair is about 100,000 nanometres wide.

Used with the camera and processor of a standard cell phone, the SPiAS becomes an optical sensor that can detect pathogens.

Sensor changes colour when water is contaminated

The SPiAS chip has receptors that reflect vivid colors when lit by a simple white LED. Pathogens in the water sample bind to the receptors in the chip, which leads to a change in the sensor’s colour, indicating that the water is contaminated.

A cell phone is used to capture and analyze the sensor’s image for color changes. Water quality data can then be transmitted using wireless networks to a central server and distributed by social media to warn people that use the water source. The research was sponsored by a Discovery grant from the Natural Sciences and Engineering Research Council of Canada (NSERC).

Researcher inspired by butterfly wings

Saini got the idea for the sensors from butterfly wings. “I have always been fascinated by these beautiful nanostructures,” he says. Once, while viewing a butterfly wing under a microscope, he accidentally dropped some water on it and the color changed. This got him thinking about whether he could generate colors in chips.

Currently, it takes days to process water samples and other optical chips being researched require expensive equipment. This new method is quick and inexpensive and uses the connectivity of cell phones to rapidly warn people about contaminated water.