A Dual-Emission Probe Based on Silicon Nanoparticles and Rhodamine B for Ratiometric Fluorescence/Colorimetric Dual-Mode Detection of Methyl Parathion.

In this study, blue fluorescent silicon nanoparticles (SiNPs) were synthesized via a hydrothermal method by using 3-(aminopropyl)triethoxysilane (APTES) and L-cysteine as precursors. Then SiNPs were combined with rhodamine B (RhB) to form an enzyme-free ratiometric fluorescence probe. Under 383 nm excitation, the SiNPs@RhB probe emitted two peaks at 457 nm and 565 nm, which could be applied to detect methyl parathion in a ratiometric fluorescence/colorimetric dual-mode detection system. In an alkaline environment, methyl parathion can be hydrolyzed and lead to its absorption peak significantly shifted to 400 nm. In the ratiometric fluorescence manner, the fluorescence of the SiNPs@RhB probe at 457 nm and 565 nm was weakened in different degrees by internal filter effect (IFE) and static quenching effect (SQE). A good linear relationship could be obtained in the range of 0.1-100 µmol/L with a detection limit of 0.03 µmol/L. Furthermore, as the concentration of methyl parathion increased, the absorbance of the SiNPs@RhB probe at 400 nm also gradually increased, accompanying a change in solution color from pink to orange. Therefore, a colorimetric method was also constructed for methyl parathion detection with linear range of 0.1-200 µmol/L and a detection limit of 0.03 µmol/L. The proposed methods could be used to detect methyl parathion in real samples of lake water, soil, gongju, and sanqi powder with satisfactory recoveries.