Istanbul Technical University creates NIR-2 sensor that detects mercury(II) ions in 10 seconds, tested in the lab

Researchers at Istanbul Technical University (ITU) have created a molecular sensor, NIR-2, that responds to mercury(II) ions by changing color and emitting near-infrared light, according to a release published by EurekAlert on 10 November 2026 eurekalert.orgEurekAlerteurekalert.orgOpen source ↗. The study appeared in Talanta and was carried out by researchers from ITU and Recep Tayyip Erdoğan University. The sensor responded in about 10 seconds, and the signal remained stable for at least 20 minutes.

How the selenium switch works

At the core of NIR-2 is a selenium-based molecule that is normally in a closed form and emits minimal light. Mercury(II) ions strongly attract selenium, and on contact they open the structure. The solution then changes from yellow to green and emits intense near-infrared light. The same reaction therefore produces both a visible color change and a fluorescent signal. The color can be seen directly or captured with a camera, while the near-infrared signal can be read with laboratory instruments and used for cellular imaging.

UV–visible spectroscopy detected mercury(II) at concentrations as low as 3.77 × 10⁻¹⁰ M, and fluorescence measurements reached 4.54 × 10⁻⁹ M.

Smartphone readout and test samples

The team also photographed samples with a Redmi Note 10S and analyzed the red and green color components. Using the ratio of these colors reduced the effect of lighting variations eurekalert.orgEurekAlerteurekalert.orgOpen source ↗. The smartphone method detected Hg²⁺ from 1.66 × 10⁻⁹ to 7.50 × 10⁻⁶ M, which the authors consider the most sensitive smartphone-based Hg²⁺ detection range reported so far. The U.S. EPA maximum contaminant level for inorganic mercury in drinking water is 2 parts per billion, or 0.002 mg/L, and the lower limit of the smartphone approach falls below it under controlled experimental conditions.

The researchers tested drinking, tap and lake water, as well as strawberries, watermelon and cherries, all intentionally spiked with known amounts of mercury. In rice, corn, beans and lentils the sensor gave semi-quantitative color responses in several cases, but its effectiveness varied with the food matrix. In three human lung cell lines, cell viability stayed above 90%, and fluorescence imaging showed a mercury-dependent signal inside the cells.

The authors note that the results do not yet make NIR-2 a ready-to-use consumer detector. Sample preparation was still required, measurements were taken under controlled lighting, and most experiments used samples with mercury added by the researchers. Testing with naturally contaminated samples, varied environmental conditions and field measurement systems is still needed. The researchers also propose that the molecular design could serve as a basis for sensors for other substances.