Rapid visual detection of aluminium ion using citrate capped gold nanoparticles

We report the visual detection of Al3+ using unlabeled gold nanoparticles (AuNPs) based on the complexation of Al3+ with citric acid, resulting in the aggregation of AuNPs. The distinction of color change can be observed by the naked eye at concentrations down to 1.0 μM which is lower than the permissable level (7.4 μM) for drinking water as defined by the World Health Organization.