Supporting Information Optical Imaging of the Non-fluorescent Nanodiamonds in Live Cells Using Transient Absorption Microscopy

Preparation of the nanodiamonds (NDs) The raw, detonated NDs (NanoCarbon Institute, Japan) were acquired as colloidal particles and then dispersed in deionized water. The raw ND colloid was carboxylated in strong oxidizing conditions as previously reported. Briefly, the colloid was treated in acid mixture of 68% HNO3 : 98% H2SO4 ( 1:3 in volumn ) in ultrasonic bath for 24 h, followed by stirring in 0.1 M NaOH at 90 °C for 2 h. After high-speed centrifugation, an additional stirring was performed in 0.1M HCl aqueous solution at 90 °C for 2 h, and finally sent for high-speed centrifugation. The pellet was resuspended in deionized water and precipitated again by high-speed centrifugation. This procedure was repeated three times to remove excessive HCl and impurities. A minute portion of the aqueous suspension was dispensed on a silicon wafer and characterized with scanning electron microscopy.