A number of applications demand imaging of wet specimens with the help of electron microscopy. Further, modification of nanomaterial properties based on specific applications requires knowledge on the mechanisms controlling dynamic processes such as self-assembly, growth, and nucleation. This can be accomplished by imaging liquid nanoparticles with electron microscopy.
This article describes the process of imaging citrate stabilized gold nanoparticles of varying sizes in liquid through Protochips’ Poseidon liquid TEM holder. Poseidon ensures a self-contained, maintainable liquid environment inside the electron microscope at the time of imaging.
The silicon nitride surface was added with 0.5µL droplet of solution containing 1.4nm and 10nm gold nanoparticles in order to to deposit gold nanoparticles on an E-chip™. Following the evaporation of solvent, the presence of gold nanoparticles on the silicon nitride surface was observed with the help of scanning TEM. In order to carry out liquid imaging, the E-chip was placed in the Poseidon holder and dispensed with 0.8µL droplet of 10% phosphate buffered saline.
A second E-chip carrying a spacer was kept over the first E-chip and the chamber was sealed vacuum-tight. A buffer solution was added to the sample at a flow rate of 50nL/s. Using an FEI CM200FEG TEM that operates at 200kV, the aqueous nanoparticles were imaged. The thickness of the liquid was measured as ~ 0.8µm.
Results and Discussion
Figures 1a and 1b show the images of gold nanoparticles that appear dark against the bright background of the liquid. The darkness in the image is seen clearly at lower magnification and shows a combination of amplitude and diffraction contrast.
Diffraction contrast can be observed at the time of intensity variations, especially in large crystalline particles. The variations are not in line with the smooth, symmetric variation expected from an incoherent signal.
These variations can be observed in the gold particles in the bright field image and the corresponding inverted intensity profile as shown in Figure 2. The resolution was found to be ~5nm.
Figure 1a and 1b. TEM bright field images of the gold nanoparticles
Figure 2. Inverted intensity profile
The Poseidon TEM holder from Protochips is available in two or three port configurations. The two-port configuration ensures constant liquid flow throughout the specimen, while the three-port configuration allows introduction and mixing of reagents during imaging process.
The Poseidon TEM holder can be used to observe a wide range of dynamic processes such as particle-particle interactions, nucleation, growth and self-assembly.
Protochips, Inc. is a rapidly growing early-stage company focused on providing the world's leading materials and life sciences research breakthrough analytical tools for targeted research and development of nano-scale materials.
Using its proprietary technology, Protochips is addressing the market need by transforming the most widely used tools in nanotechnology – electron and optical microscopes - from cameras into complete nano-scale laboratories.
Protochips' core competency lies in the application of semiconductor techniques to development of MEMS devices capable of providing heat, electrical, liquid and gas environments to samples in situ.
This information has been sourced, reviewed and adapted from materials provided by Protochips.
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