Abstract
BackgroundTransmission electron microscopy (TEM) remains an important technique to investigate the size, shape and surface characteristics of particles at the nanometer scale. Resulting micrographs are two dimensional projections of objects and their interpretation can be difficult. Recently, electron tomography (ET) is increasingly used to reveal the morphology of nanomaterials (NM) in 3D. In this study, we examined the feasibility to visualize and measure silica and gold NM in suspension using conventional bright field electron tomography.ResultsThe general morphology of gold and silica NM was visualized in 3D by conventional TEM in bright field mode. In orthoslices of the examined NM the surface features of a NM could be seen and measured without interference of higher or lower lying structures inherent to conventional TEM. Segmentation by isosurface rendering allowed visualizing the 3D information of an electron tomographic reconstruction in greater detail than digital slicing. From the 3D reconstructions, the surface area and the volume of the examined NM could be estimated directly and the volume-specific surface area (VSSA) was calculated. The mean VSSA of all examined NM was significantly larger than the threshold of 60 m2/cm3.The high correlation between the measured values of area and volume gold nanoparticles with a known spherical morphology and the areas and volumes calculated from the equivalent circle diameter (ECD) of projected nanoparticles (NP) indicates that the values measured from electron tomographic reconstructions are valid for these gold particles.ConclusionThe characterization and definition of the examined gold and silica NM can benefit from application of conventional bright field electron tomography: the NM can be visualized in 3D, while surface features and the VSSA can be measured.
Highlights
Transmission electron microscopy (TEM) remains an important technique to investigate the size, shape and surface characteristics of particles at the nanometer scale
We examined the feasibility of three-dimensional visualization of silica and branched gold NM in suspension using conventional bright field (BF) electron tomography (ET)
We examined whether such materials can be defined as a NM based on the measurement of their volume-specific surface area (VSSA) from its electron tomographic reconstruction
Summary
Transmission electron microscopy (TEM) remains an important technique to investigate the size, shape and surface characteristics of particles at the nanometer scale. Resulting micrographs are two dimensional projections of objects and their interpretation can be difficult. Electron tomography (ET) is increasingly used to reveal the morphology of nanomaterials (NM) in 3D. TEM remains an important technique to measure the size and surface topography of materials at the nanometer level. Because the resulting micrographs are two-dimensional projections of the studied objects, their interpretation can be difficult, when the particles are complex, agglomerated or lack symmetry. In such cases, fine ultrastructural details are blurred due to superposition of projected features. As data acquisition, alignment and reconstruction software evolves to be more user-friendly; ET is increasingly used to reveal the morphology and to evaluate the threedimensional characteristics of NP and nanoparticle ensembles [4,5]
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