Researchers in Iran based at Razi University have now developed a simple test to quickly and accurately measure lead (II) levels in aqueous solutions down to very low concentrations. The test uses a solution of azacrown ether-modified AuNPs, which changes colour in the presence of the toxic metal ion. This colour change is visually discernible by an appearance of the surface plasmon band (SPB) at 520 nm. The recognition mechanism is attributed to the unique structure of monoazacrown ether attached to AuNPs and metal sandwiches co-ordinated between two azacrown ether moieties that are attached to separate AuNPs. This inter-particle cross-linking (see image) results in aggregation and an apparent colour change from brown to purple.

The sensor is selective against alkali-, alkaline-earth- and heavy-transition-metal ions. Such selectivity is essential for applications involving real environmental samples. Compared with many current optical chemosensors for lead (II), this sensor is rapid, cost-effective and enzyme-free. The system allows easy detection of lead ions by the naked eye without resorting to any expensive instruments. Significantly, this method can, in principle, be used to detect other metal ions by changing the structure and the size of ionophores that selectively bind other metal ions.

More details can be found in the journal Nanotechnology.