An ultra-sensitive and colorimetric sensor for copper and iron based on glutathione-functionalized gold nanoclusters

Here, we report an ultra-sensitive and colorimetric sensor for the detection of Fe³⁺ or Cu²⁺ successively using glutathione-functionalized Au nanoclusters (GSH-AuNCs). For GSH-AuNCs can catalytically oxidize peroxidase substrates, such as 3, 3', 5, 5'-tetramethylbenzidine (TMB), colored products are formed in the presence of H₂O₂. While upon the addition of Fe³⁺ or Cu²⁺ into the GSH-AuNCs-TMB-H₂O₂ system, diverse color and absorbance of the system was obtained due to the self oxidation of Fe³⁺ and the inhibition of peroxidase-like activity of GSH-AuNCs. With the introduction of ethylene diamine tetraacetic acid (EDTA) or ammonium fluoride (NH₄F) to GSH-AuNCs-TMB-H₂O₂+Cu²⁺ system or GSH-AuNCs-TMB-H₂O₂+Fe³⁺ system respectively, a restoration of color and absorbance of system was realized. On the basis of above phenomenon, a colorimetric and quantitative approach for detecting Fe³⁺ and Cu²⁺ was developed with detection limit of 1.25 × 10^-9 M and 1.25 × 10^-10 M respectively. Moreover, the concentration of Fe³⁺ and Cu²⁺ in human serums was also accurate quantified by this method. So this design strategy realized the simple and simultaneous detection of Fe³⁺ and Cu²⁺, suggesting significant potential in clinical diagnosis.