A method for attaching nanodiamonds (NDs) to H-terminated diamond devices displaying surface conductivity, configured as an ion-sensitive field-effect transistor and resistor sensor, is demonstrated. From Hall effect measurements, there was minimal sign of degradation of the p-type surface conductivity after ND coating (∼ 1013 carriers/ cm2, ∼27 cm 2/V s). In response to pH changes, the device showed an improved response to the as-hydrogenated sensor, from 19 mV/pH to a maximum of 37 mV/pH. Configured in resistor mode, exposure to 2,4-dinitrotoluene vapor gave rise to sensitive detection, while the uncoated H-terminated device exhibited reaction instability. The mechanisms behind these observations are discussed.