Specific and sensitive colorimetric detection of Al3+ using 5-mercaptomethyltetrazole capped gold nanoparticles in aqueous solution

Contamination of food and drinking water by health-risk levels of Al3+ calls for convenient assays. Here, we report a method to visibly detect Al3+ at room temperature. Firstly, the chelating ligand of 5-mercaptomethyltetrazole (MMT) was synthesized and modified on the surface of AuNPs through the strong Au–S interaction to form a MMT–AuNP probe, which can remain well-dispersed and stable in an aqueous solution for a long time. Upon the addition of Al3+, the interparticle crosslinking induced aggregation (color change from red to blue) of MMT–AuNPs was triggered through the Al3+–MMT interaction. Under optimal conditions, the absorbance ratio (A620/A520) of MMT–AuNPs is linear within the Al3+ concentration range from 1.0 to 10.0 μM, and the detection limit (3σ) was as low as 0.53 μM. Moreover, an interference study showed that this MMT–AuNP probe discriminated Al3+ from a wide range of environmentally dominant metal ions and anions. The practical utility of the new method was demonstrated by determining Al3+ in several environmental water and human urine specimens, obtaining satisfactory results. Being a rapid, convenient and cost-effective method, it should become a powerful alternative to conventional methods for selective quantification of Al3+ in routine laboratory practice or rapid on-site assay.