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Updated: Nov 6, 2025
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Dispersion of Nanomaterials in Aqueous Media: Towards Protocol Optimization
Published on: December 25, 2017
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Quantification of Nanoparticles in Dispersions Using Transmission Electron Microscopy
Ralf Kaegi1, Martin Fierz2, Bodo Hattendorf3
1Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600Dübendorf, Switzerland.
Summary
This study presents a method for nanoparticle characterization using an ultrasonic nebulizer and transmission electron microscopy. While underestimating particle number concentration, it enables reproducible nanoparticle deposition for size and morphology analysis.
Area of Science:
- Materials Science
- Nanotechnology
- Analytical Chemistry
Background:
- Accurate nanoparticle characterization, including particle size and number concentration (PNC), is crucial for nanomaterial applications.
- Transmission electron microscopy (TEM) is a gold standard for nanoparticle size but faces challenges in sample preparation for PNC estimation.
- Current methods for preparing nanoparticle samples for TEM-based PNC analysis are often complex and difficult.
Purpose of the Study:
- To develop a reproducible method for nanoparticle deposition on TEM grids for morphological analysis and PNC estimation.
- To evaluate the effectiveness of an ultrasonic nebulizer (USN) coupled with an electrostatic precipitator for nanoparticle aerosolization and deposition.
- To assess the accuracy of PNC estimations derived from TEM images using this novel approach.
Main Methods:
- Utilized an ultrasonic nebulizer (USN) to convert nanoparticle suspensions into dried aerosols.
- Employed an electrostatic precipitator integrated with an aerosol monitor for depositing nanoparticles onto TEM grids.
- Analyzed SiO2 nanoparticles (50–200 nm) using TEM to assess deposition uniformity and estimate PNC.
Main Results:
- Achieved reproducible and even deposition of nanoparticles in the center of TEM grids.
- Observed a deposition efficiency of approximately 2% for the electrostatic precipitator and 7% for the USN.
- TEM-derived PNC underestimated suspension PNC by up to a factor of three, attributed to NP aggregation and droplet coagulation within the USN.
- Single particles remained the dominant feature in the PNC.
Conclusions:
- The developed method provides reproducible nanoparticle deposition on TEM grids, suitable for morphological studies.
- While the method currently underestimates PNC, it offers a viable approach for estimating nanoparticle concentrations in suspensions.
- Further optimization of the USN process could improve the accuracy of PNC quantification.
