Researchers have developed an advanced optical sensor capable of real-time detection of extremely low arsenic levels in water. This technology could enable at-home testing, allowing individuals to monitor their water quality with ease.
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Arsenic contamination is a significant environmental and public health issue affecting millions worldwide. It occurs naturally when geological processes release arsenic from rocks and soil into groundwater and can be worsened by activities such as mining, industrial waste disposal, and the 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. 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.
Sunil Khijwania, Lead Researcher, Indian Institute of Technology Guwahati
Published in the Optica Publishing Group journal Applied Optics, the study details how the sensor leverages an optical fiber and a phenomenon known as localized surface plasmon resonance.
The device successfully detected arsenic at concentrations as low as 0.09 parts per billion (ppb), significantly below the World Health Organization's maximum permissible limit of 10 ppb. It also demonstrated reliable performance when tested on real drinking water samples from various locations.
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. 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.
Sunil Khijwania, Lead Researcher, Indian Institute of Technology Guwahati
A User-Friendly Yet Accurate Sensor
While conventional spectroscopy methods for detecting arsenic are highly accurate and sensitive, they often require bulky, expensive equipment that can be complex and time-consuming to use. To address this challenge, researchers have developed an optical fiber sensor that offers a low detection limit while being cost-effective and user-friendly enough for routine arsenic monitoring in drinking water.
The new sensor is built by coating the inner core of an optical fiber with gold nanoparticles and a thin layer of a specially designed nanocomposite made of aluminum oxide and graphene oxide. This nanocomposite selectively binds to arsenic ions. A portion of the light traveling through the fiber extends into the surrounding cladding due to the evanescent wave created by total internal reflection. By removing a small section of the cladding, the evanescent wave is exposed to the environment.
As light moves through the fiber, the evanescent wave interacts with the gold nanoparticles, triggering localized surface plasmon resonance—a phenomenon where electrons on the nanoparticle surface oscillate in response to specific wavelengths of light. If arsenic is present, it binds to the nanocomposite, causing a measurable shift in the surface plasmon resonance wavelength. This shift enables highly accurate detection of even trace amounts of arsenic in water.
Thorough Performance Assessment
The researchers tested the sensor with varying concentrations of arsenic ion solutions and found that it consistently delivered reliable detection across the entire concentration range. After further optimization, they examined additional parameters, confirming that the sensor maintained accuracy during both increasing and decreasing arsenic levels. It also demonstrated a rapid response time of just 0.5 seconds.
The sensor achieved a maximum resolution of ± 0.058 ppb of arsenic and showed minimal variation when analyzing identical samples over four separate days within an 18-day period. To further validate its accuracy, researchers compared its readings with those from inductively coupled plasma mass spectrometry (ICP-MS), a widely used method for arsenic detection. The sensor's results showed a relative percentage difference of less than 5 %, demonstrating strong agreement between the two techniques.
To assess its real-world performance, the team tested the sensor on drinking water samples collected from various locations in Guwahati, India. The sensor remained reliable 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. In the long term, this new approach could potentially be modified to create a new wave of affordable and accessible environmental monitoring tools.
Sunil Khijwania, Lead Researcher, Indian Institute of Technology Guwahati
While the sensor is ready for field use, the researchers note that developing a more affordable and user-friendly optical source and detector would be key to enabling widespread adoption.
Journal Reference:
Banoo, F. and Khijwania, K., S. (2025) Localized surface plasmon resonance-based optical fiber arsenic ion sensor employing Al2O3/GO nanocomposite. Applied Optics. doi.org/10.1364/AO.544358