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Determination of the volume-specific surface area by using transmission electron tomography for characterization and definition of nanomaterials.

Van Doren EA, De Temmerman PJ, Francisco MA, Mast J - J Nanobiotechnology (2011)

Bottom Line: Segmentation by isosurface rendering allowed visualizing the 3D information of an electron tomographic reconstruction in greater detail than digital slicing.The mean VSSA of all examined NM was significantly larger than the threshold of 60 m(2)/cm(3).The 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: EM-unit, CODA-CERVA, Groeselenberg 99, Brussels, Belgium.

ABSTRACT

Background: 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. 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.

Results: The 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 m(2)/cm(3). 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.

Conclusion: The 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.

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Electron tomographic analyses of silica NM. The micrographs, taken at 0°, show one (Figure 3A) and two aggregates (Figure 3C) consisting of multiple primary subunits of NM-200 and NM-203, respectively. Figure 3B and Figure 3D show the corresponding ET reconstructions. Bars: 200 nm.
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Figure 3: Electron tomographic analyses of silica NM. The micrographs, taken at 0°, show one (Figure 3A) and two aggregates (Figure 3C) consisting of multiple primary subunits of NM-200 and NM-203, respectively. Figure 3B and Figure 3D show the corresponding ET reconstructions. Bars: 200 nm.

Mentions: It is not evident to envisage the structure of the silica reference materials NM-200 and NM-203 appropriately by conventional bright field TEM (Figure 3A and 3C). Their relatively low molar mass results in a low contrast, while their complex morphology results in blurring of ultrastructural details due to superposition of projected features. Electron tomographic reconstruction in three dimensions circumvents these difficulties. Figure 3B and 3D, and the corresponding Additional files 2 and 3, illustrate that both the precipitated silica NM-200 and the pyrogenic silica NM-203 consist of aggregates of very complex morphology composed of a variable number of interconnected primary subunits. Although the site where an aggregate interacts with the grid can be found in the 3D reconstruction as a relatively flat surface, structures of primary subunits remain extended in the z-direction, resulting in similar dimensions along the three axes. This suggests a limited flexibility of the material. Measurement in 3D space showed that individual aggregates in both NM-200 and NM-203 are composed of similarly sized primary subunits. The size of the subunits of the aggregates of NM-200 is relatively constant: they measure approximately 20 nm in diameter. The size of the subunits of different aggregates of NM-203 is variable: the subunits of the left aggregate shown in Figure 3D measure, for example, 8 to 12 nm in diameter, while the subunits of the right aggregate measure approximately 20 nm in diameter. In any of the tilt series of NM-200 and NM-203, diffraction contrast was observed, confirming their amorphous structure. The surface area and volume of NM-200 and NM-203 were measured for five ET reconstructions and the VSSA was calculated (Table 1). For both materials, the mean VSSA were significantly different (P < 0.05) from 60 m2/cm3.


Determination of the volume-specific surface area by using transmission electron tomography for characterization and definition of nanomaterials.

Van Doren EA, De Temmerman PJ, Francisco MA, Mast J - J Nanobiotechnology (2011)

Electron tomographic analyses of silica NM. The micrographs, taken at 0°, show one (Figure 3A) and two aggregates (Figure 3C) consisting of multiple primary subunits of NM-200 and NM-203, respectively. Figure 3B and Figure 3D show the corresponding ET reconstructions. Bars: 200 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3113930&req=5

Figure 3: Electron tomographic analyses of silica NM. The micrographs, taken at 0°, show one (Figure 3A) and two aggregates (Figure 3C) consisting of multiple primary subunits of NM-200 and NM-203, respectively. Figure 3B and Figure 3D show the corresponding ET reconstructions. Bars: 200 nm.
Mentions: It is not evident to envisage the structure of the silica reference materials NM-200 and NM-203 appropriately by conventional bright field TEM (Figure 3A and 3C). Their relatively low molar mass results in a low contrast, while their complex morphology results in blurring of ultrastructural details due to superposition of projected features. Electron tomographic reconstruction in three dimensions circumvents these difficulties. Figure 3B and 3D, and the corresponding Additional files 2 and 3, illustrate that both the precipitated silica NM-200 and the pyrogenic silica NM-203 consist of aggregates of very complex morphology composed of a variable number of interconnected primary subunits. Although the site where an aggregate interacts with the grid can be found in the 3D reconstruction as a relatively flat surface, structures of primary subunits remain extended in the z-direction, resulting in similar dimensions along the three axes. This suggests a limited flexibility of the material. Measurement in 3D space showed that individual aggregates in both NM-200 and NM-203 are composed of similarly sized primary subunits. The size of the subunits of the aggregates of NM-200 is relatively constant: they measure approximately 20 nm in diameter. The size of the subunits of different aggregates of NM-203 is variable: the subunits of the left aggregate shown in Figure 3D measure, for example, 8 to 12 nm in diameter, while the subunits of the right aggregate measure approximately 20 nm in diameter. In any of the tilt series of NM-200 and NM-203, diffraction contrast was observed, confirming their amorphous structure. The surface area and volume of NM-200 and NM-203 were measured for five ET reconstructions and the VSSA was calculated (Table 1). For both materials, the mean VSSA were significantly different (P < 0.05) from 60 m2/cm3.

Bottom Line: Segmentation by isosurface rendering allowed visualizing the 3D information of an electron tomographic reconstruction in greater detail than digital slicing.The mean VSSA of all examined NM was significantly larger than the threshold of 60 m(2)/cm(3).The 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: EM-unit, CODA-CERVA, Groeselenberg 99, Brussels, Belgium.

ABSTRACT

Background: 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. 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.

Results: The 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 m(2)/cm(3). 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.

Conclusion: The 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.

Show MeSH