Catalytic activity of catalase–silica nanoparticle hybrids: from ensemble to individual entity activity† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04921d Click here for additional data file.

For all measurements (UV-Vis and electrochemistry), the unmodified SiNPs were used as received and diluted to the desired concentration with ultrapure water from Millipore featuring a resistivity of not less than 18.2 MΩ.cm. The following procedure was used for modifying the SiNP with catalase: 79.5 L of SiNPs were added to 119.7 L of water. Next, 20 L of bovine catalase from stock solution (Sigma, 45 mg/ml) were added. Last, 54.8 L of 50 mM citrate phosphate buffer (pH=5.4) were added as well. The solution was left overnight for incubation at room temperature. Next, the solution was centrifuged (9000 RPM, Eppendorf 5430-R) for 30 min, the supernatant was removed and the pellet was washed with 219 L of water and 55 L of the citrate buffer. The centrifugation and washing process was repeated three times to insure that there is no residual catalase left in solution.