Structuring of noble metal nanoparticles on transition metal dichalcogenide nanosheets induces significantly enhanced electronic, optical, and catalytic functions. However, the synthesis of multifunctional hybrids is always time-consuming and involves multiple steps. Herein, a ternary Au nanoparticle-ferrocene-WS2 nanosheet (AFW) composite has been prepared by a facile one-step sonochemical approach. Stripped WS2 nanosheets were functionalized with ferrocene monocarboxylic acid (FMC) and gold nanoparticles (AuNPs) by making use of the strong coordinative interaction of carboxyl groups with tungsten atoms. The AuNPs decorating the WS2 nanosheet not only increase the water solubility of WS2 nanosheet and surface area of the modified electrode, but also act as electron transport bridges to aid the tunneling of electrons from the small redox molecule, FMC, through the space to the electrode on which they are mounted. Furthermore, the ternary AFW nanocomposite could effectively avoid the leaching of FMC from the nanocomposite matrix and provided a suitable environment for the immobilized biomolecules. Combining the immune magnetic beads technology and the AFW nanocomposite with aforementioned advantages, a high-performance electrochemical immunosensor was successfully developed using carbohydrate antigen 72-4 (CA72-4) as a model analyte. A linear relationship in the range of 2-50 U/L for the detection of CA72-4 was found with a low detection limit of 0.6 U/L. In addition, the biosensor showed excellent performance in selectivity, stability, and reproducibility. Thus, this work not only proposes a facile avenue for preparing a 2D WS2 nanocomposite with multifunctional properties but also opens up a new method to extend the application of WS2-based materials in biological sensing.