Disposable Amperometric Immunosensor for Detecting Toxoplasma Gondii-Specific IgM Based on Graphene and CeO2-Au

Abstract

Toxoplasma gondii-specific IgM (Tg-IgM) is a sensitive and reliable marker for early diagnosing toxoplasmosis infection in pregnant women. In this study, a disposable amperometric immunosensor for sensitive detecting Tg-IgM was constructed based on graphene (GP) and CeO2-Au nanoparticle. The GP was treated with chitosan (CS) to obtain a stable graphene-chitosan (GPCS) composite membrane. The CeO2-Au nanoparticle which was used for the preparation of the amperometric immunosensor was synthesized by the hydrothermal method. GPCS composite membrane was first assembled onto the screen-printed carbon electrode (SPCE) for adsorbing the CeO2-Au nanoparticle. The toxoplasma gondii antigen (Tg-Ag) was subsequently adsorbed by CeO2-Au nanoparticle to obtain the proposed immunosensor. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to characterize the construction process of the immunosensor. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were used to study the electrochemical properties of the immunosensor. The results indicated that, CS employed in this study improved the dispersion and homogeneity of GP, as well as enhance the stability of the proposed immunosensor. The use of GPCS composite membrane and CeO2-Au nanoparticle had good conductivity and prominent biocompatibility, which excellently improved the sensitivity of the immunosensor. In the optimal conditions, the proposed immunosensor can be applied to quantify the concentration of Tg-IgM in a wide linear range from 7.5×10 AU•mL to 24 AU•mL with a correlation coefficient of -0.998 and a low detection limit of 4.4×10 AU•mL (S/N=3). The novel proposed immunosensor for detecting Tg-IgM in human serum specimens with satisfactory results had also been proved. In addition, the Tg-IgM contents determined by the immunosensor agreed well with the ELISA measurement. Furthermore, the proposed amperometric immunosensor exhibited some advantages, such as high selectivity, long-term stability, good repeatability, low sample consumable, and short analysis time, which were suitable for detecting toxoplasma infection in pregnant women.