Electronic-Tongue Colorimetric-Sensor Array for Discrimination and Quantitation of Metal Ions Based on Gold-Nanoparticle Aggregation

Sensor arrays, called "electronic tongues", provide an alternative to time-consuming detection approaches. In this work, a colorimetric-sensor array composed of three recognition receptors (cysteine, l-glutathione, and melamine) was developed for fast discrimination of toxic metal ions. Different recognition receptors exhibited different binding affinities toward metal ions, causing diverse gold-nanoparticle (AuNP)-aggregation behaviors and generating distinct colorimetric response patterns. As "fingerprints", these response patterns can be quantitatively analyzed by linear-discriminant analysis (LDA). The sensor array achieved good discrimination of six kinds of metal ions (Ti4+, Cr3+, Mn2+, Fe3+, Pb2+, and Sn4+) in deionized water and real samples. It possessed good reproducibility and exhibited a linear range of 100–900 nM (R2 = 0.97) for Ti4+, 100–900 nM (R2 = 0.97) for Cr3+, 100–900 nM (R2 = 0.98) for Mn2+, 100–1000 nM (R2 = 0.92) for Sn4+, 100–800 nM (R2 = 0.94) for Fe3+, and 100–900 nM (R2 = 0.97) for Pb2+. The sensor array shows feasible potential in environmental monitoring and simplification of water-quality analysis.