Prof. JIANG Changlong's research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has developed a highly sensitive ratiometric fluorescent probe that can detect heavy metal trivalent chromium (Cr³⁺) in the environment.

"This probe uses porphyrin nanoparticles formed by a block copolymer as the sensing core. The captured fluorescence color information can be converted into digital data and analyzed in real time using a smartphone," said Prof. JIANG.

The study was published in Sensors and Actuators B: Chemical.

Chromium pollution in the environment mainly involves hexavalent chromium ions (Cr⁶⁺) and Cr³⁺, both of which pose serious threats to ecological systems and human health. Most existing tests focus on the detection of Cr⁶⁺, often overlooking Cr³⁺. However, Cr³⁺ also has a significant impact on soil, water, and plant and animal growth.

With this in mind, the researchers developed a ratio fluorescence sensing system to achieve rapid and sensitive on-site detection of Cr³⁺ in the environment.

The system consists of two main parts: Blue Carbon Dots (BCDs) as a reference and porphyrin nanoparticles (TAPP-NPs) as sensors. When Cr³⁺ is present, the TAPP-NPs trap it by forming a special structure. Under UV light, the TAPP-NPs stop glowing due to charge transfer in this special structure, but the BCDs continue to glow. As more Cr³⁺ is added, the fluorescence changes from red to blue.

To meet different environmental requirements, two portable sensing devices were designed to work with a smartphone APP for color recognition. The APP can detect the color change, convert it to digital data, and store it for analysis. This allows for quantitative detection and easy visualization of the results.

The fluorescence sensing strategy provides a new approach for real-time monitoring of Cr³⁺, paving the way for rapid, on-site, and intuitive detection of heavy metals in the environment.

 Schematic of a portable smart sensing device based on porphyrin nanoparticles to visualize and detect Cr³⁺ in the environment. (Image by LI Xingzhen)