Ability to detect biomolecules with a simple and cost-effective approach has been very demanding in today's medicine. The nanoparticles and two-dimensional materials have been extensively used within this field in devices with high selectivity and sensitivity. Here, we report the use of MoS2 nanoparticles (MoS2 NPs) as a signal-enhancing label in a standard immunoassay test. MoS2 NPs were prepared by a bipolar electrochemistry method. The current response during the hydrogen evolution reaction catalyzed by MoS2 was measured. This current was directly proportional to the amount of the MoS2 NPs and thus also to the concentration of desired protein. The immunoassay containing the MoS2 NPs displays extraordinary low limit of detection (1.94 pg mL-1), good selectivity, and reproducibility. This MoS2 NP detection system could have profound implication for analytical applications.