A l-tryptophan-Cu(II) based fluorescence turn-on probe for detection of methionine

In this paper, a sensitive and simple method for the determination of methionine (Met) was developed based on the fluorescence quenching and recovery of l-tryptophan (l-Trp). In pH 9.7 Na2CO3-NaHCO3 buffer medium, Cu2+ could react with l-Trp to form 1:1 complex because of the strong electrostatic interaction, which resulted in the fluorescence quenching of l-Trp. However, the quenched fluorescence of l-Trp could be recovered upon the addition of Met due to the strong affinity between Cu2+ and thiols. Under the optimized experimental conditions, the recovered fluorescence intensities were linearly proportional to the concentration of Met within the range of 4.8×10−6–3.0×10−5 mol L−1. The detection limit was 1.4×10−6 mol L−1.