Precise estimation of HPHT nanodiamond size distribution based on transmission electron microscopy image analysis

Fluorescent nanodiamonds (NDs) are extremely promising fluorescent probes and sensors in experimental biology. For these applications, NDs obtained from high-pressure, high-temperature (HPHT) synthesis are used. Commercial HPHT NDs are polydisperse and of irregular shape. In this work, we used image analysis of transmission electron microscopy (TEM) micrographs to determine the actual size distribution of an HPHT ND sample with high precision. We developed novel TEM sample preparation procedure, which includes hydrophilization of a carbon-coated TEM grid by UV/ozone treatment and subsequent charge reversal and charge-controlled adsorption of nanoparticles. This method results in NDs spread evenly on the grid and radically improves the quality of TEM samples. Image analysis of TEM micrographs of commercial NDs revealed an unexpectedly high abundance of sub-10nm NDs in the sample. This method can also be used for preparing TEM samples of other negatively charged nanoparticles, such as citrate-stabilized gold. [Display omitted] •High precision size distribution of HPHT nanodiamond using TEM image analysis is performed.•Samples are spread evenly on hydrophilized, charge reversed carbon-coated grids.•Unexpectedly high abundance of sub-10nm NDs is revealed in a commercial nanodiamond.•The method is useful also for other negatively charged nanoparticles, for example gold.