Ultra-sensitive optical sensors for toxic trace metals can be made from nanostructured materials
The detection of toxic trace metals, such as lead and mercury, can be achieved with expensive laboratory instruments such as atomic emission spectrometers. Optical sensor approaches, which allow for naked eye detection as well as on-site and real-time measurement, are often limited by low sensitivity.
Now, Sherif El-Safty and co-workers1 at the National Institute of Advanced Industrial Science and Technology in Sendai, Japan have developed a highly sensitive and selective optical sensor, which changes colour when toxic metals are present. Four different chromophores (colour-changing molecules) were grafted onto ring-shaped silica monoliths with cage like nanostructures and each responded to the presence of a different metal ion, either lead, antimony, cadmium or mercury. The cage structure allowed for the rapid diffusion of metals, lowering the response time to under a minute.
This new optical ‘sink’ material has detection limits as low as 1.4 parts per billion for mercury and 4.1 parts per billion for antimony — lower than all previously reported visual detection methods. Because even trace levels of these common environmental pollutants may be harmful, such high sensitivity is essential. Furthermore, the rapid response time, low cost and potential for recycling of this new material make it a promising candidate for environmental monitoring.
Balaji, T., El-Safty, S. A., Matsunaga, H., Hanaoka, T. & Mizukami, F. Angew. Chem. Int. Edn (2006). 10.1002/anie.200602453