Fig.S1

2.5. Preparation of immobilized enzyme

D-amino acid dehydrogenase immobilized in ZIF-8 (DAADH/ZIF-8) were prepared by mixing zinc nitrate solution (0.16 M, 500 μL), enzyme solution (500 μL) and 2-methylimidazole (0.16 M, 500 μL) together and then shaking at 4 ℃, 200 rpm, 30 min. The mixing solution was centrifugated at 4 ℃, 8000 rpm, 15 min. The supernatant was collected to measure the protein concentration for further determination of enzyme loading rate. The precipitate was washed with deionized water three times, and then resuspended it with PBS buffer (200 mM, pH 7.4).
D-amino acid dehydrogenase immobilized in hybrid materials of ZIF-8 and RGO (DAADH/ZIF-8/RGO) was prepared by mixing zinc nitrate solution (0.16 M, 500 μL), enzyme solution (500 μL), 2-methylimidazole (0.16 M, 500 μL) and RGO (1 mg/mL,500 μL). After shaking at 4 ℃, 200 rpm for 4 h, the solution was centrifuged at 4 ℃, 8000 rpm, 15 min. The supernatant was collected and measure the protein concentration for further determination of enzyme loading rate. The precipitate was washed with deionized water three times, and then resuspended it with PBS buffer (200 mM, pH 7.4).
One-step separation and immobilization of enzyme from crude solution was investigated. D-amino acid dehydrogenase immobilized in hybrid materials of ZIF-8, RGO and Ni (DAADH-ZIF-8/RGO/Ni-DAADH) was prepared by mixing zinc nitrate solution (0.16 M, 500 μL), NiCl2 (0.08 M, 500 μL), enzyme solution (500 μL), 2-methylimidazole (0.16 M, 500 μL) and RGO (1 mg/mL,500 μL), and followed by the shaking, centrifugation and resuspending as above.

2.6. Morphology characterization

Morphology analysis of immobilized enzyme was carried out by scanning electron microscopy with a Zeiss Sigma scanning electronic microscopy (SEM) (Carl-Zeiss AG, Germany). JEOL JFC 1600 (JEOL, Tokyo, Japan) was used to spray platinum on the sample to make it conductive.

2.7. Reusability

Reusability of immobilized enzyme was studied by recycling the enzymatic reaction for seven times. At the ending of each reaction, the immobilized enzyme was re-collected by centrifugation at 8000 rpm for 15 min (4 °C) and washed with PBS buffer (pH 7.4). Initial enzyme activity of first cycle was set as 100 %, and the remaining activity was counted for percent form (%) compared with that of the first reaction.

2.8. Thermostability

The enzyme was incubated in water bath at 50 °C for 10 h. The enzyme activity was measured by taking samples every 2 h (at 0,2,4,6,8,10 h). The relative enzyme activity was calculated by setting the enzyme activity of the unincubated enzyme solution as 100%.