A team of researchers from the Indian Institute of Technology Guwahati has created a new optical sensor that offers real-time detection of extremely low levels of arsenic in water — potentially paving the way for households to test for arsenic and monitor their own water quality.

The team explained that arsenic contamination happens when natural geological processes release arsenic from rocks and soil into groundwater. This process can be intensified by activities such as mining, industrial waste disposal as well as the use of arsenic-based pesticides.

Source: Sunil Khijwania, Indian Institute of Technology Guwahati

"Consuming arsenic-contaminated water can lead to severe health conditions including arsenic poisoning and cancers of the skin, lung, kidney and bladder," the team added. "By creating a sensor that is sensitive, selective, reusable and cost-effective, we aim to address the need for a reliable and user-friendly tool for routine monitoring, helping to protect communities from the risks of arsenic exposure."

The new sensor, according to its developers, features an optical fiber and relies on an optical phenomenon called localized surface plasmon resonance, which, during testing, enabled the detection of arsenic levels as low as 0.09 parts per billion (ppb) — this number is 111 times lower than the maximum permissible limit of 10 ppb as established by the World Health Organization.

The inside core of the optical fiber was coated with gold nanoparticles along with a thin layer of a nanocomposite composed of aluminum oxide and graphene oxide, which selectively binds to arsenic ions. Meanwhile, some of the light traveling through the core extends into the surrounding fiber cladding due to the evanescent wave generated by total internal reflection. Removing the cladding from a small section of the fiber exposes this evanescent wave to the surrounding environment.

Further, as light passes through the optical fiber, the evanescent wave engages with the gold nanoparticles, thereby inducing localized surface plasmon resonance wherein electrons on the nanoparticle surface simultaneously oscillate in response to specific light wavelengths. In the event that arsenic is present, it binds to the nanocomposite, producing a measurable shift in the surface plasmon resonance wavelength and allowing for the accurate detection of trace amounts of arsenic in water.

Capable of providing an analysis of water samples in just 0.5 seconds, the sensor demonstrated reliable performance in the lab when tested on drinking water samples sourced from diverse locations and conditions. The team explained that this sensor could potentially save lives by preventing exposure to harmful levels of arsenic.

The team detailed the new sensor in the article: “Localized Surface Plasmon Resonance based Novel Optical Fiber Arsenic Ion Sensor Employing Al2O3/GO Nanocomposite,” which appears in the journal Applied Optics.