A colorimetric chemosensor for the sequential detection of copper ion and amino acids (cysteine and histidine) in aqueous solution

A simple and selective colorimetric chemosensor 1 was reported for the sequential detection of Cu²⁺, cysteine (Cys) and histidine (His) in aqueous solution. The presence of Cu²⁺ led to a distinct naked-eye color change from pale yellow to orange. Also, the receptor enabled analysis of Cu²⁺ ions with a sensitivity limit of 0.37 μM, which is far below the WHO acceptable limit (31.5 μM) in drinking water. 1 could be also used as a practical, visible colorimetric test strip for Cu²⁺ (down to 10 μM) in aqueous media. Moreover, the resulting 1-Cu²⁺ complex sensed cysteine and histidine with an absorption change via UV-visible or a naked-eye color change, although His and Cys were indistinguishable with the method proposed herein.