Characterization of nanomaterials in food by electron microscopy

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…Electron microscopy is presently the predominant technique to investigate the presence, aggregation state, location, and composition of ENPs in ecotoxicological tests and on/in organisms [68][69][70] (see case study II and also Dudkiewicz et al [71], which gives a comprehensive overview of EM techniques for ENP analysis in food matrices). Both the high-resolution TEM and the field emission gun-equipped SEM or scanning transmission electron microscopy systems provide the necessary spatial resolution to visualize particles down to a few nanometers in diameter.…”

“…However, the low sensitivity of EDS techniques will prevent most attempts based on the recognition of trace impurities or naturally accompanying elements. Drying of samples and high vacuum artifacts may be prevented by low vacuum SEM (environmental SEM; ESEM) and wet-SEM techniques; however, they do not provide the necessary resolution to image the smaller fraction of ENPs (approximately <30 nm) [71]. For cryogenic and embedding techniques, the reader is referred to Dudkiewicz et al [71] and the references therein.…”

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

“…Thus, for an optical microscope operating at wavelengths, λ from 400 to 800 nm and numerical aperture (NA) of ~ 1, Abbe's diffraction limit d = λ/2NA, gives a resolution of approx. 200 nm 26 up to 10 nm with some improvement, 27 while for an EM working with an acceleration voltage from 100 to 1000 keV, the theoretical value of the wavelength will be from 0.0037 to 0.00087 nm 28 (See Table 1). Nevertheless, in the current state-of-the-art, the best TEM resolution, by using double aberration correction, is 0.047 nm 29 while SEM microscopes achieve resolutions in the range of 1 nm (high resolution) to 3 nm (conventional).…”

“…Nevertheless, in the current state-of-the-art, the best TEM resolution, by using double aberration correction, is 0.047 nm 29 while SEM microscopes achieve resolutions in the range of 1 nm (high resolution) to 3 nm (conventional). 28 In TEM, the electron beam Depending on the electron source used it is possible to change the spatial resolution, for instance, a low brightness tungsten electron source typically provides 50-100 nm resolution while brighter sources such as LaB 6 filaments allow a resolution below 5-10 nm. Using field emission guns (sharply-pointed Müller-type emitter), the electron beam is more coherent reaching more intense beam of high energy than in conventional thermionic emitters such as tungsten and LaB 6 filaments.…”

“…In ESEM, the chamber containing the sample holder remains under a few mbar of gas as well as being saturated with water vapour. 28 Here, the vapour pressure can be decreased to achieve better NP imaging conditions (since only the surface of the water droplets are imaged at 100 % humidity, hiding the NPs that are inside them). The conductive coating over the sample in SEM is suppressed in ESEM, since the vapour gaseous layer around the NPs becomes ionized and neutralizes all charged regions (collisions of the electrons with the gas generate positive ions that prevent the buildup of charges on insulating samples).…”