A newly developed optical sensor offers a straightforward and highly sensitive method for real-time detection of minute arsenic levels in water, reports Optica. This innovative technology has the potential to facilitate household testing, allowing individuals to monitor their own water quality with ease.
Arsenic contamination poses a significant environmental and public health concern, impacting millions globally. It primarily results from natural geological processes that release arsenic from rocks and soil into groundwater. Additionally, activities such as mining, industrial waste disposal, and the use of arsenic-based pesticides can exacerbate the issue.
“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.”
Published in the Optica Publishing Group journal Applied Optics, the research details a sensor that utilizes an optical fiber along with localized surface plasmon resonance to detect arsenic concentrations as low as 0.09 parts per billion (ppb). This sensitivity is 111 times lower than the World Health Organization's maximum allowable limit of 10 ppb. Furthermore, the sensor demonstrated consistent performance when tested on real drinking water samples from various sources.
“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 cost-effective and user-friendly sensor
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New easy-to-use optical fiber sensor achieves sensitive and real-time detection of extremely low levels of arsenic in water. Credit: Sunil Khijwania, Indian Institute of Technology Guwahati
Traditional spectroscopy-based arsenic detection methods, while highly accurate, often require sophisticated, expensive, and bulky equipment. These complexities make routine monitoring difficult. To bridge this gap, the researchers developed an optical fiber sensor that offers not only high sensitivity but also affordability and ease of use for everyday arsenic testing in drinking water.
To construct the sensor, the researchers applied a thin coating of gold nanoparticles and a unique nanocomposite made of aluminum oxide and graphene oxide to the inner core of an optical fiber. This nanocomposite selectively binds with arsenic ions. A portion of the transmitted light extends beyond the fiber’s core due to an optical effect known as an evanescent wave. By exposing this wave to the surrounding environment, the sensor achieves arsenic detection through localized surface plasmon resonance—a phenomenon in which electrons on the nanoparticle surface oscillate in response to specific light wavelengths. The presence of arsenic causes a measurable shift in the resonance wavelength, allowing precise detection of even trace amounts in water.
The researchers rigorously tested the sensor with arsenic ion solutions of varying concentrations. The results confirmed its reliability and accuracy across different levels of contamination. After further optimization, additional testing revealed the sensor's consistency in detecting arsenic even when concentrations fluctuated from low to high and vice versa. Impressively, it exhibited a rapid response time of just 0.5 seconds.
The sensor demonstrated a resolution of ±0.058 ppb and showed minimal variation in repeated tests over an 18-day period. To verify accuracy, the researchers compared its measurements with those obtained through inductively coupled plasma mass spectrometry (ICP-MS), a widely used method for arsenic analysis. The optical fiber sensor displayed a relative percentage difference of less than 5%, indicating a strong correlation between the two techniques.
Further assessments involved testing drinking water samples collected from various locations in Guwahati, India. Even under these real-world conditions, the sensor continued to deliver reliable performance.
“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.”
While the sensor is fully capable of detecting arsenic in real-world applications, the researchers highlight the need for a more economical and user-friendly optical source and detector to enable widespread adoption.
