A highly sensitive and selective molecularly imprinted electrochemical sensor modified with TiO2-reduced graphene oxide nanocomposite for determination of podophyllotoxin in real samples

To obtain an electrochemical sensor with high sensitivity and good selectivity for determination of podophyllotoxin (PPT), a kind of graphene composite (rGO@TiO2) with multi-layer structure and excellent conductivity was prepared by hydrothermal treatment of reduced graphene oxide (rGO) and TiO2 nanoparticles. The composite was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and a sensor using rGO@TiO2 as a signal amplification element was fabricated by in-situ polymerization of PPT imprinted membrane (PPT-MIM) on the rGO@TiO2 modified glassy carbon electrode (PPT-MIM/rGO@TiO2/GCE). The structure and electrochemical performance of PPT-MIM/rGO@TiO2/GCE as well as the mechanism with superior conductivity of rGO@TiO2 exceeding the ones of the mixture of TiO2 and rGO (TiO2-rGO) or the pure TiO2 and rGO were explained with different technologies. Under the optimal conditions, the present sensor showed a linear response for the determination of PPT by differential pulse voltammetry (DPV) in the range of 1.0 × 10−9 − 1.0 × 10−7 mol L−1 (R2 = 0.9980) and 1.0 × 10−7 − 3.0 × 10−4 mol L−1 (R2 = 0.9991) with the limit of quantification is 1.0 × 10−9 mol L−1 and the limit of detection of 3.0 × 10−10 mol L−1. The sensor not only possesses high sensitivity and good selectivity, but also exhibits excellent repeatability and stability. It has been used to detect PPT in real samples (including Podophyllum hexandrum, human urine and human whole blood) with satisfied recoveries of 92.0%–102.3%.