Fabrication of a ratiometric fluorescence nanoprobe for detecting tryptophan enantiomers

A novel ratiometric fluorescence nanoprobe was developed to detect tryptophan enantiomers with high selectivity and sensitivity. Fluorescein (FL) was doped into SiO₂ nanoparticles with little dye leakage, acting as an internal reference signal. The chiral center of L-histidine (L-His) was introduced by partially replacing the carboxyl on the surface of SiO₂. The response signal of Eu³⁺ was coordinated with carboxyl to obtain the FL@SiO₂-Eu/His nanoprobe. The nanoprobe shows enantioselective luminescence responses for tryptophan enantiomers. The red emission of Eu³⁺ can be effectively quenched by the tryptophan enantiomers, but the quenching efficiency is different due to the different interactions with the chiral recognition sites. The fluorescence intensity ratio (I₆₁₃/I₅₁₅) shows excellent linearity with tryptophan enantiomers in the range of 0-100 μM (R² > 0.99). The limit of detection (LOD) is 1.0 μM and 1.3 μM for L-tryptophan (L-Trp) and D-tryptophan (D-Trp), respectively. The FL@SiO₂-Eu/His nanoprobe shows good selectivity and specific recognition in serum actual samples. In addition, the nanoprobe can realize visual detection under UV light due to the obvious color change. This work provides an innovative idea for the development of new probes in the detection field.