New Sensor Detects Toxic Metals in Water with High Accuracy

A team of researchers from the Indian Institute of Technology Bombay (IIT Bombay) and Monash University, Australia, has developed a cost-effective sensor capable of detecting toxic heavy metals in water. The sensor, made from a copper-based metal-organic framework (MOF), matches the performance of DNA-based sensors, which are considered the gold standard for water quality testing.

Heavy metals, which are elements with high atomic weights and densities, are widely used in industries such as manufacturing and agriculture. However, their toxic, persistent, and bioaccumulative nature poses significant environmental and health risks.

According to a report by The Energy and Resources Institute (TERI), groundwater in 718 districts across India is contaminated with heavy metals like arsenic, cadmium, chromium, and lead. The Ministry of Environment, Forest and Climate Change (MoEF&CC) has also identified 320 locations with a high probability of heavy metal contamination. Exposure to these metals can lead to severe health issues, including damage to the skin, bones, brain, and other organs, particularly in children. Efficient detection methods are crucial to mitigating these risks.

To tackle this issue, the research team, with support from the Department of Biotechnology (DBT), Government of India, developed a sensor utilizing a copper-based MOF. MOFs are highly porous materials consisting of metal ions linked by organic compounds, offering exceptional surface area and tunability. These properties make them ideal for applications in environmental monitoring.

For this study, the researchers designed a MOF using copper (Cu) as the metal node, connected to Tetrakis(4-carboxyphenyl) porphyrin (TCPP), forming copper-tetracarboxyphenylporphyrin (Cu-TCPP). This structure, known as a paddle-wheel MOF, maximizes the surface area in contact with water, significantly enhancing its ability to detect heavy metal ions such as lead (Pb), cadmium (Cd), and mercury (Hg), even at trace levels.

The Cu-TCPP MOF detects heavy metals in two ways:

1. Substitution: Some metal ions, such as lead, replace copper in the MOF structure, altering its electronic properties and allowing researchers to quantify the contamination.

2. Accumulation: Other metals, like cadmium and mercury, do not replace copper but instead build up on the MOF surface, forming molecular islands. At high concentrations, this accumulation leads to structural failure, which can be measured to determine contamination levels.

This MOF involves two Cu atoms binding to each carboxyphenyl arm of the TCPP molecule, hence forming the characteristic paddle-wheel structure. This means that other metal ions with similar configurations would be able to replace Cu in the structure and maintain the overall order without causing structural collapse. Other metal ions, especially heavy metal ions, can also accumulate on the MOF lattice.

Prashanth Kannan, Study First Author and Student, IIT Bombay-Monash Research Academy

The sensor was tested on tap and lake water samples, successfully detecting lead, cadmium, and mercury even at very low concentrations. It performed well despite the presence of potential interfering substances such as alkali metals, debris, and other large particles, demonstrating its reliability across different environmental conditions.

Compared to commercially available state-of-the-art sensors, the Cu-TCPP sensor showed comparable or superior performance.

“When faced with a highly regular periodic lattice arrangement such as the Cu-TCPP MOF, they initially accumulate on the surface of the MOF, then at high concentrations can cause the failure of the MOF structure. By identifying the differences in electrochemical waveform and intensity (during the failure), we are able to accurately estimate nanomolar levels of heavy metals in water,” explained Prashanth.

The researchers tested the sensor on water samples from both taps and lakes, where it successfully detected lead, cadmium, and mercury—even in trace amounts. Notably, the sensor maintained its accuracy despite the presence of potential interferences, such as alkali metals, debris, and other large particles. This demonstrated its reliability across various conditions.

When compared to state-of-the-art sensors currently on the market, the device performed just as well, if not better, in most cases.

“Our device has the least complexity and comparable sensing limits to the best of the current DNA-based sensors (the gold standard for sensing devices),” remarked Prashanth.

Despite its strong performance, the sensor does have some limitations. The MOF structure tends to degrade after prolonged exposure to heavy metals, making it a single-use device. However, in the case of water quality sensors, one-time use is the industry standard for low-cost devices. As a result, Prashanth notes that reusability isn’t a necessary feature and shouldn’t be considered a drawback.

The major bottleneck with this type of device lies in material fabrication costs. MOFs are difficult to coat over large areas, but there are ongoing efforts by various research groups worldwide to make manufacturing possible on a large scale.

Prashanth Kannan, Study First Author and Student, IIT Bombay-Monash Research Academy

This technology has the potential to enhance public health while also demonstrating how scientific advancements can address critical environmental issues. Looking ahead, Prashanth is already focused on tackling the next set of challenges.

Currently, there are several topics of major interest worldwide that need materials like MOFs to address them, like detecting Perfluorooctane sulfonic acid (PFOS), perfluoroalkyl substances (PFAS), arsenic and chromium in drinking water and tap water.

Prashanth Kannan, Study First Author and Student, IIT Bombay-Monash Research Academy

Journal Reference:

Kannan, P., et al. (2025) Tripartite Detection and Sensing of Toxic Heavy Metals Using a Copper-Based Porphyrin Metal–Organic Framework. ACS Applied Materials & Interfaces.  doi.org/10.1021/acsami.4c12974.