WASHINGTON — Researchers have developed a new optical sensor that provides a simple way to achieve real-time detection of extremely low levels of arsenic in water. The technology could enable household testing for arsenic, empowering individuals to monitor their own water quality.
Arsenic contamination is a serious environmental and public health challenge affecting millions of people around the world. This contamination occurs when natural geological processes release arsenic from rocks and soil into groundwater and can be exacerbated by mining, industrial waste disposal and use of arsenic-based pesticides.
"Consuming arsenic-contaminated water can lead to severe health conditions including arsenic poisoning and cancers of the skin, lung, kidney and bladder," said lead researcher Sunil Khijwania from the Indian Institute of Technology Guwahati . "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."
In the Optica Publishing Group journal Applied Optics , the researchers describe their new sensor, which uses an optical fiber and an optical phenomenon known as localized surface plasmon resonance. They used it to detect arsenic levels as low as 0.09 parts per billion (ppb), 111 times lower than the maximum permissible limit of 10 ppb established by the World Health Organization. The sensor also exhibited reliable performance when tested on real drinking water samples from diverse locations and conditions.
"The highly sensitive sensor provides analysis within just 0.5 seconds and demonstrates a high degree of reusability, repeatability, stability and reliability, making it a powerful tool for monitoring and ensuring safer water quality," said Khijwania. "In the future, this technology could make it much easier for people to check whether their drinking water is safe, potentially saving lives by preventing exposure to harmful arsenic levels."
A user-friendly yet accurate sensor
Although conventional spectroscopy methods for detecting arsenic are highly accurate and sensitive, they tend to require complex, bulky, expensive equipment that is time-consuming and complicated to use. To fill this critical gap, the researchers developed an optical fiber sensor that not only has a low detection limit but is also cost-effective and user-friendly enough for routine arsenic monitoring in drinking water.
To make the new sensor, the researchers coated the inside core of a fiber with gold nanoparticles and a thin layer of a unique nanocomposite composed of aluminum oxide and graphene oxide, which selectively binds to arsenic ions. A portion of the light traveling through the core also extends into the surrounding fiber cladding due to the evanescent wave created by total internal reflection. By removing the cladding in a small section of the fiber, the evanescent wave is exposed to the environment.
As light travels through the optical fiber, the evanescent wave interacts with gold nanoparticles, triggering localized surface plasmon resonance — a phenomenon where electrons on the nanoparticle surface collectively oscillate in response to specific light wavelengths. If arsenic is present, it will bind to the nanocomposite, causing a measurable shift in the surface plasmon resonance wavelength and enabling accurate detection of trace arsenic in water.
Thorough performance assessment
The researchers tested the sensor using varying concentrations of arsenic ion solutions, finding that it produced consistent and reliable detection of arsenic across the tested concentration range. After additional optimization, they tested other parameters, showing that the sensor produced consistent results during both low-to-high and high-to-low changes in arsenic ion concentration and achieved a fast response time of just 0.5 seconds.
The sensor exhibited a maximum resolution of ± 0.058 ppb of arsenic and showed negligible variations in results for samples with identical arsenic concentrations analyzed on four separate days over an 18-day period. The researchers also compared sensor measurements to those obtained with inductively coupled plasma mass spectrometry (ICP-MS), which is commonly used for arsenic measurements. The sensor showed a relative percentage difference of less than 5%, indicating strong agreement between the two methods.
To evaluate the real-world applicability of the sensor, the researchers tested it on drinking water samples collected from different locations in the city of Guwahati in India. The sensor maintained reliable performance under these varied conditions.
"These investigations established that the proposed optical fiber sensor offers a highly sensitive, selective, fast, cost-effective, straightforward and easy solution for arsenic detection in real field conditions," said Khijwania. "In the long term, this new approach could potentially be modified to create a new wave of affordable and accessible environmental monitoring tools."
The researchers note that although the sensor is ready for real-world use in detecting arsenic, a less expensive and easier-to-use optical source and detector would need to be developed to enable widespread application.
Paper: F. Banoo, S. K. Khijwania, "Localized Surface Plasmon Resonance based Novel Optical Fiber Arsenic Ion Sensor Employing Al2O3/GO Nanocomposite," Applied Optics, 64, 1019-1027 (2025).
DOI: 10.1364/AO.544358
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