A dual-channel visual sensing system for recognition of multiple metal ions

Here, we propose a simple, rapid, and effective colorimetric sensor array for discrimination of metal ions. The sensor array was constructed using two sensing channels, i.e., gold nanoparticles (AuNPs)- Tetramethylbenzidine (TMB)-H₂O₂ and AuNPs-O-phenylenediamine (OPD)-H₂O₂ reaction systems. The presence of metal ions with positive charges would lead to the corresponding surface charge change of negatively charged AuNPs, resulting in diverse catalytic performances of citrate-modified AuNPs, accompanied by a substantial colorimetric performance of oxidation products of TMB and OPD. Employing the diversity of colorimetric responses of metal ions to the two sensing channels, nine metal ions including Cr³⁺, Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mg²⁺, K⁺, and Cd²⁺ were well distinguished with a discrimination accuracy of 100% at a concentration as low as 50 nM. Further experiment showed that the sensor array was also capable of discriminating and quantifying metal ions at various concentrations, as well as the identification of metal ion mixtures. The feasibility of the sensor array was also verified by the successful identification of the nine metal ions in river water samples.