Multiplex sensor for detection of different metal ions based on on-off of fluorescent gold nanoclusters

In this study, a multiplex fluorescence sensor for successive detection of Fe(3+), Cu(2+) and Hg(2+) ions based on "on-off" of fluorescence of a single type of gold nanoclusters (Au NCs) is described. Any of the Fe(3+), Cu(2+) and Hg(2+) ions can cause quenching fluorescence of Au NCs, which established a sensitive sensor for detection of these ions respectively. With the introduction of ethylene diamine tetraacetic acid (EDTA) to the system of Au NCs and metal ions, a restoration of fluorescence may be found with the exception of Hg(2+). A highly selective detection of Hg(2+) ion is, thus, achieved by masking Fe(3+) and Cu(2+). On the other hand, the masking of Fe(3+) and Cu(2+) leads to the enhancement of fluorescence of Au NCs, which in turn provides an approach for successive determination of Fe(3+) and Cu(2+) based on "on-off" of fluorescence of Au NCs. Moreover, this assay was applied to the successful detection of Fe(3+), Cu(2+) and Hg(2+) in fish, a good linear relationship was found between these metal ions and the degree of quenched fluorescent intensity. The dynamic ranges of Hg(2+), Fe(3+) and Cu(2+) were 1.96×10(-10)-1.01×10(-9), 1.28×10(-7)-1.27×10(-6) and 1.2×10(-7)-1.2×10(-6) M with high sensitivity (the limit of detection of Fe(3+) 2.0×10(-8) M, Cu(2+) 1.9×10(-8) M and Hg(2+) 2×10(-10) M). These results indicate that the assay is suitable for sensitive detection of these metal ions even under the coexistence, which can not only determine all three kinds of metal ions successively but also of detecting any or several kinds of metal ions.