A series of hydroxyquinolines show promise as elements in sensor arrays for detecting metal ions in water.
Some heavy metals such as mercury have no known vital or beneficial effect on organisms and their accumulation over time in the body can cause serious illness. Because they cannot be degraded or destroyed, they have significant potential to impact human health and the whole environment. Thus, sensing of heavy metal ions in water is important for maintaining the well-being of humans and protecting the environment, said Pavel Anzenbacher of Bowling Green State University, US.
A sensor array is made up of several sensor elements. These elements are not highly selective toward specific analytes, but the specificity of the device comes from recognition of response patterns such as fluorescence. This pattern originates from interactions of the analyte with each of the sensors in the array. This response pattern is unique to the analyte like a fingerprint.
"The colour depends on the substituents and, crucially, the metal ion"
Anzenbacher's team designed sensors comprising an 8-hydroxyquinoline ligand and blue emitting-residues. The quinoline forms luminescent chelates with a number of metal ions. It also shows a handy turn-on signal, because it is non-fluorescent in water but emits a blue-green colour when it binds to a metal. The colour depends on the 8-hydroxyquinoline substituents and, crucially, the metal ion.
By extending the length of these conjugated chromophores (the colour-emitting groups) they were able to vary the ratio of the blue to green emissions from the metal chelates. Changes in the blue and green emissions of the metal complexes are then used to distinguish the cations.
'The novelty of our approach is the use of one receptor (ligand) type and varying the chromophore to generate variable signal output,' said Anzenbacher.