Since the isolation of graphene in 2004, two-dimensional (2D) materials such as transition metal dichalcogenide (TMD) have attracted numerous interests due to their unique van der Waals structure, atomically thin body, and thickness-dependent properties. In recent years, the applications of TMD in public health have emerged due to their large surface area and high surface sensitivities, as well as their unique electrical, optical, and electrochemical properties. In this review, we focus on state-of-the-art methods to modulate the properties of 2D TMD and their applications in biosensing. Particularly, this review provides methods for designing and modulating 2D TMD via defect engineering and morphology control to achieve multi-functional surfaces for molecule capturing and sensing. Furthermore, we compare the 2D TMD-based biosensors with the traditional sensing systems, deepening our understanding of their action mechanism. Finally, we point out the challenges and opportunities of 2D TMD in this emerging area.