Fluorescence sensor array based on amino acids-modulating quantum dots for the discrimination of metal ions

We developed an easily extensible fluorescence sensor array based on amino acids-modulating QDs for the discrimination of nine metal ions. Two amino acids (Glutamine and Arginine) were assembled with two quantum dots including 3-mercaptopropionic acid capped Mn-ZnS QDs (MPA-QDs) and alpha-thioglycerol capped Mn-ZnS QDs (TG-QDs), achieving six across-reactive sensing elements. Amino acids as the modulators imparted the diversity and differential detection of metal ions, because they could bind QDs and also form complexes with metal ions through their carboxyl, amino, and hydroxyl groups. Therefore, the fluorescence response signals for metal ions could be either enhanced or decreased. This sensing system allowed the accurate classification of nine metal ions in pure water at 0.5 μM and tap water at 3.0 μM. Moreover, two metal ions with different oxidation state Fe³⁺ and Fe²⁺, as well as their binary mixtures were well distinguished. Our sensor array was capable of the quantitative analysis of metal ions, showing a linear range from 0.5 μM to 20 μM for Co²⁺, Ni²⁺, Mn²⁺, and Fe²⁺. The results demonstrated that the number of sensing elements was easily extensible by using amino acids as QDs regulators. This strategy will provide a new direction to establish the sensitive array sensing systems.