Synergistic recognition SERS sensor of MgO-protected AgNPs functionalized with tryptophan and β-cyclodextrin for trace monosultap analysis

A highly sensitive surface-enhanced Raman spectroscopy (SERS) approach was established for the detection of monosultap using the nanosubstrate of β -CD/Trp/MgO/AgNPs which was MgO-protected silver nanoparticles (AgNPs) assembled tryptophan (Trp) and β -cyclodextrin ( β -CD). Six nanosubstrates including AgNPs, MgO/AgNPs, Trp/AgNPs, β -CD/MgO/AgNPs, Trp/MgO/AgNPs and β -CD/Trp/MgO/AgNPs were compared for their enhancement effect on monosultap. Among them, β -CD/Trp/MgO/AgNPs had the greatest enhancement effect, with an enhancement factor (EF) reaching up to 1.95 × 10 6 . The nanosubstrate of β -CD/Trp/MgO/AgNPs was characterized by various instrumental techniques, such as transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), zeta potential, X-ray diffraction (XRD), thermogravimetric analysis (TGA), ultraviolet-visible (UV–vis) and Fourier transform infrared (FT-IR). The binding of β -CD/Trp/MgO/AgNPs with monosultap was studied in detail. The optimum experimental conditions were confirmed through single-factor experiments and response surface analysis. The interferences from the coexisting substances (common metal ions, glucose and congeneric drugs) were investigated to evaluate the method selectivity. Under the optimal conditions, the standard curve equation of monosultap was established within the concentration range of 2.00 × 10 −8 –1.00 × 10 −6  mol L −1 , with detection limit (LOD) of 0.970 nmol L −1 (3 σ / S ). The SERS approach was utilized for detecting monosultap in several vegetables and fruits with the recoveries from 96.3 % to 105 %.