The accurate identification of disease markers is essential for the early diagnosis and treatment of conditions, particularly tumors such as hepatocellular carcinoma. However, achieving fast and quantitative analysis of disease markers remains a considerable challenge, especially for multivariate testing. Thus, a synergistic multifunctional nanoreactor composed of phosphotungstate (PW₁₂), a metal–organic framework (MOF), and integrated Au nanoparticles (PW₁₂@ZIF-67-Au), was developed as a dual-mode probe, using colorimetric and electrochemical methods to detect dopamine (DA) and alpha-fetoprotein (AFP). The incorporation of MOFs creates a nanoconfined microenvironment that effectively modulates the active sites of POMs, synergistically catalyzing the generation of reactive oxygen species (ROS) and activating oxidase-mimicking activity. This enables both colorimetric and electrochemical sensing, along with antibacterial performance. AFP was detected within a linear range of 0.01–100 ng/mL, with a limit of detection (LOD) of 7.65 pg/mL, while DA was detected from 0.3 to 20 μM with an LOD of 183 nM. Importantly, recovery rates from serum samples were substantial and demonstrated comparable accuracy to clinical enzyme-linked immunosorbent assays. This work not only offers valuable guidelines for creating multifunctional nanoreactors for biosensing and early diagnosis but also lays the foundation for developing a versatile and promising strategy to improve human health.