Controlling the physical and chemical properties of nanoparticles requires a comprehensive study on a clear and accurate image of the particles. A highly sophisticated scanning electron microscope has long been regarded as the most important tool for this purpose.
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Scanning Electron Microscope
The scanning electron microscope (SEM) is a microscopy technique used for magnifying infinitesimal features or objects that are otherwise invisible to the naked eye.
In contrast to optical light microscopes, which utilize light to create imaging, SEM uses electron beams. Electrons resolve finer characteristics of materials to a far larger extent due to their shorter wavelength.
The first scanning microscope was built in 1935 by a German scientist, Max Knoll (Laperrière & Reinhart, 2014). Since its discovery, the technology has been advanced further to meet the necessary demand in research and development.
SEM consists of lenses for concentrating electrons to a fine beam, raster equipment for traversing the beam, detectors for monitoring electrons generated by the specimen, and an image display system.
Secondary electrons, backscattered electrons, and transmitted electrons are some of the ways the electron beam interacts with the specimen (Reimer, 1998).
The images are generated by scanning a high-energy electron beam across the surface of the specimen. (Erdman, Bell, & Reichelt, 2019).
Advantages of SEM in Studying Nanoparticles
Nanotechnology has contributed enormously to the prospect of quicker and more powerful computers, economic power sources, and life-saving medical technologies.
Nanoparticles exhibit higher reactivity than analogous bulk materials due to increased solubility, a higher proportion of surface atoms relative to the interior of a structure, distinctive magnetic properties, electronic structure, and catalytic response (Phan & Haes, 2019).
Due to their excellent favorable properties, nanoparticles are being explored in all domains where nano-size plays a critical role in deciding fundamental qualities.
SEM provides unrivaled imaging and detecting capabilities as the analysis of structural morphology demonstrates how the macromolecules conduct their functions at the atomic or molecular level. The fact that images of three-dimensional objects are frequently accessible to quick intuitive and clear interpretation by the observer is a key component in the SEM's success.
SEM has several advantages, including speedy imaging, quick results, time-efficient processing, and quick turnaround time.
The detection of nanoparticles can also be employed in the biomedical field to allow for regulated drug release from the substrate (Mitchell, et al., 2020). It can help to enhance medication absorption and reduce dosing frequency, as well as solve the problem of non-compliance with prescribed therapy.
Current and Future Prospects of Nanoparticle Detection with SEM
SEM is one of the most powerful types of equipment for studying and analyzing the geometry and chemical compositions of nanostructures, which is considered a strong contender to replace current electronic chips made up of silicon.
Due to silicon’s poor electron-hole mobility and inefficiency at high temperatures, adding nanoparticles, such as graphene additives, significantly improves the thermal properties and toughness of the material (Kaźmierczak-Bałata & Mazur, 2018).
In this case, the use of SEM gives the ability to detect nanoparticles and investigate their properties and macro flaws, such as porosity, cracks, secondary phases, and microscopic defects.
SEM is also one of the few techniques available that can provide precise information on nanoparticle cellular attachment in the biomedical field.
Recently, researchers used SEM to study the nanoparticles interacting with in vitro bio-engineered microtissues to accelerate the inclusion of nanoparticles in nanomedicine (Sun, Lee, Chen, & Hoshino, 2020).
Previously, a team adopted SEM to demonstrate that gold-coated magnetic nanoparticles can be employed to alleviate the problem of the magnetic core of the nanocapsule being protected from oxidation (Chen, Wang, Erramilli, & Mohanty, 2006). This feature is employed in the creation of magnetic nanocapsules for biomedical applications.
In a recent paper, Leandro, Hastrup, Reznik, Cirlin, & Akopian investigated the excellent optical properties of GaAs quantum dots in AlGaAs nanowires that are considered a promising candidate for scalable quantum photonics.
The team adopted SEM to study nanowires, although GaAs quantum dots that were embedded into a nanowire were not visible. At the current state, the SEM shows the limitation of being confined to a solid-state sample that is vacuum-compatible.
A strong insulating sample must be coated with conductive materials so that they can be examined and analyzed under optimal conditions. This adds additional time to what was already considered a lengthy operation of the SEM, giving more room for human error.
Recently, Thermofisher Scientific has introduced an automated Phenom desktop SEM that offers time-efficient analysis by eliminating human-biased error (Thermo Fisher Scientific Phenom-World BV., 2022).
This SEM provides imaging of a large variety of small features of different particles within a reasonable time. The future of SEM looks forward to contemplating the addition of next-level automation that can effectively analyze multiple layers of materials.
References and Further Reading
Chen, Y., Wang, X., Erramilli, S., & Mohanty, P. (2006). Silicon-based nanoelectronic field-effect pH sensor with local gate control. Appl. Phys. Lett. doi:10.1063/1.2392828
Erdman, N., Bell, D., & Reichelt, R. (2019). Springer Handbook of Microscopy. Springer. doi:10.1007/978-3-030-00069-1_5
Kaźmierczak-Bałata, A., & Mazur, J. (2018). Effect of carbon nanoparticle reinforcement on mechanical and thermal properties of silicon carbide ceramics. Ceramics International. doi: 10.1016/j.ceramint.2018.03.034
Laperrière, L., & Reinhart, G. (2014). CIRP Encyclopedia of Production Engineering. Springer. doi: 10.1007/978-3-642-20617-7
Leandro, L., Hastrup, J., Reznik, R., Cirlin, G., & Akopian, N. (2020). Resonant excitation of nanowire quantum dots. npj Quantum Information. doi: 10.1038/s41534-020-00323-9
Lin, Q., Fathi, P., & Chen, X. (2020). Nanoparticle delivery in vivo: A fresh look from intravital imaging. eBioMedicine. doi:10.1016/j.ebiom.2020.102958
Mitchell, M., Billingsley, M., Haley, R., Wechsler, M., Peppas, N., & Langer, R. (2020). Engineering precision nanoparticles for drug delivery. Nature Reviews Drug Discovery. doi:10.1038/s41573-020-0090-8
Phan, H., & Haes, A. (2019). What Does Nanoparticle Stability Mean? J Phys Chem C Nanomater Interfaces. doi:10.1021/acs.jpcc.9b00913
Reimer, L. (1998). Scanning Electron Microscopy. doi:10.1007/978-3-540-38967-5
Sun, M., Lee, J., Chen, Y., & Hoshino, K. (2020). Studies of nanoparticle delivery with in vitro bio-engineered microtissues. Bioact Mater. doi: 10.1016/j.bioactmat.2020.06.016
Thermo Fisher Scientific Phenom-World BV. (2022). The Future of Scanning Electron Microscopy with SEM Automation. AZoM: https://www.azom.com/article.aspx?ArticleID=17919 (Accessed on 17 March 2022)
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