Using first-principles calculations, we investigate the electron transport properties of monolayers of phosphorene and molybdenum disulfide (MoS 2 ) for use as potential hydrogen peroxide sensors. Excessive production of hydrogen peroxide (H 2 O 2 ) in the human body can be an indication of disease. Thus, the availability of a cost-effective and simple to use sensor with single molecule sensitivity is of high importance. Using the DFT-NEGF approach (density functional theory together with the nonequilibrium green functional formalism), we find that the adsorption of hydrogen peroxide on the two-dimensional (2D) monolayers display distinctive electron transmission and current−voltage characteristics compared to the pristine substrates, with phosphorene exhibiting the greater effect. This indicates that these structures could serve as potential H 2 O 2 sensors. The atomic mechanisms responsible are identified through calculation of the density of states, electronic band gap, molecular projected self-consistent Hamiltonian states, and charge transfer.