Nanodiamonds with controlled surface termination were used in this study. For ND-COOH, commercially available carboxylated detonation NDs (from Carbodeon, Vantaa and International Technology Center, USA) were dispersed in DI water at a concentration of 10 mg/mL using an ultrasonic bath. For the preparation of ND-OH, 350 mg of detonation ND (Gansu Lingyun Corp.) were first milled in an attrition mill according to literature procedure, then dispersed in ca. 50 mL of deionized water and treated for 15 min in an ice-cooled ultrasonic bath. Then, Fe(II)sulfate heptahydrate (14.6 g) was added and the mixture dispersed for another 15 min. Subsequently, 7 mL of conc. sulfuric acid and 7 mL of H2O2 solution (30%) was added and the mixture sonicated for ~ 90 min while keeping the temperature at 0 °C. 130 mL of DI water were added to stop the reaction and the hydroxylated diamond was precipitated and washed in consecutive centrifugation/washing cycles with water (3x), 3M HCl (3x), acetone (3x), water (3x) until neutral pH was reached and the inorganic components were removed. The material was centrifuged and dried in vacuo. For the reduction of residual carbonyl groups, a borane reduction was performed as the second step. The dried NDs treated with the Fenton reagent was dispersed first in dry THF, then 15 mL of 1M borane solution in dry THF was added dropwise and the reaction mixture stirred for 5 days in a nitrogen atmosphere. After addition of 30 mL of 3M HCl the product ND-OH was purified in consecutive centrifugation-washing cycles with water (3x), acetonitrile (3x), acetone (3x), isopropanol (3x) and water (3x). The particles can be isolated by centrifugation and subsequent drying in vacuo. Hydrogenation of NDs, yielding ND-H, was realized by H2 plasma treatment using the same milled detonation ND as for ND-OH. 30 mg of initial ND were placed in a quartz tube and exposed to a H2 microwave plasma with a gas pressure of 12 mbar, a gas flow of 10 standard cubic centimetres per minute and a microwave power of 250 W, for 20 min. ND-H were then dispersed in ultrapure water (18.2 MΩ.cm) by ultrasonication (Hielscher UP400s, 300 W, 24 kHz) for 1h under cooling, and centrifuged (40 min, 2400g) to remove aggregates. The final concentration was calculated by measuring the mass of residue after drying a calibrated volume of the initial suspension.