What unit is used to measure nanoparticles?
Characterization of nanoparticles
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For airborne nanoparticles, techniques for measuring size include cascade impactors, electrical low-pressure impactors, mobility analyzers, and time-of-flight mass spectrometers.  For nanoparticles in suspension, techniques include dynamic light scattering, laser diffraction, field flow fractionation, particle tracking analysis, size exclusion chromatography, centrifugal sedimentation, and atomic force microscopy.  For dry materials, techniques for measuring size include electron microscopy, atomic force microscopy, and X-ray diffraction.  Back-calculation from surface area measurements are commonly employed, but these are subject to error for porous materials.[9]  Additional methods include hydrodynamic chromatography, static light scattering, multiangle light scattering, nephelometry, laser-induced breakdown detection, and ultraviolet–visible spectroscopy;[4] as well as near-field scanning optical microscopy, confocal laser scanning microscopy, capillary electrophoresis, ultracentrifugation, cross-flow filtration, small-angle X-ray scattering, and differential mobility analysis.[6]  Use of an environmental scanning electron microscope avoids morphological changes caused by the vacuum required for standard scanning electron microscopy, at the cost of resolution.[4][6]