The Core–shell Structure ZIF-67/MIL-101 (Fe)-Modified Carbon Paper Electrode: High Sensitivity and Selectivity for the Determination of Baicalin

Baicalin (Bn) is one of the flavonoids with various biological activities, and its accurate determination is of great significance to clinical medicine. The new “MOF-on-MOF” materials have a broad application prospect. ZIF-67 and MIL-101(Fe) are typical metal–organic frame (MOF) materials, which have the advantages of flexible structure, large specific surface area, large porosity, and adjustable pore size. In this paper, a disposable and sensitive Bn electrochemical sensor based on ZIF-67/MIL-101(Fe) composite modified carbon paper (CP) electrode was developed for the first time. The sensing nanomaterials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) was used to evaluate the electrochemical behavior of Bn on different modified electrodes. The results showed that ZIF-67/MIL-101(Fe)/CP exhibited a well-defined redox peak compared with bare CP, ZIF-67/CP, and MIL-101(Fe)/CP, which was attributed to the synergistic effect of ZIF-67 and MIL-101(Fe). Under optimal conditions, the electrochemical sensor was able to quantify Bn in the ranges of 0.01 ~ 3 µM and 3 ~ 6 µM with a detection limit (LOD) as low as 0.009 µM (S/N = 3). In addition, the sensor was successfully used for the quantitative analysis of Bn in Dual yellow oral liquid with reliable results.