Sizing Nanoparticles in Liquids: An Overview of Methods
Measuring nano- and submicron particles suspended in liquids continues to be a difficult task not only because there is no universal sizing technique but, on the contrary, because there are too many alternative methods. These are quite different in their
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When you can measure what you are speaking about, you know something about it. But when you cannot measure it, your knowledge is of a meagre and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely advanced to the stage of science. Lord Kelvin, 1883
Abstract Measuring nano- and submicron particles suspended in liquids continues to be a difficult task not only because there is no universal sizing technique but, on the contrary, because there are too many alternative methods. These are quite different in their measuring principles and for that may lead to rather different results, especially if the particles under analysis are far from spherical and exhibit broad size distributions. This chapter is mainly dedicated to the users who are not very acquainted with particle sizing issues but need to select the most adequate method to characterize their suspensions. Having in mind the size range and sample type, seven different methods were selected: besides microscopic methods, that are normally the first choice to “see” the particles, this chapter encompasses techniques based on the measurement of particles Brownian motion (DLS and NTA) and on centrifugal sedimentation (DSC and SdFFF). The operating principles of these techniques as well as their merits and limitations will be discussed. Keywords Nanoparticles • Microparticles • Light scattering • Microscopy • Sizing • Predictive, preventive and personalized medicine
M. Figueiredo () Department of Chemical Engineering, University of Coimbra, Polo II – Rua Sílvio Lima, 3030-790 Coimbra, Portugal e-mail: [email protected] J. Coelho (ed.), Drug Delivery Systems: Advanced Technologies Potentially Applicable in Personalised Treatment, Advances in Predictive, Preventive and Personalised Medicine 4, DOI 10.1007/978-94-007-6010-3__3, © Springer ScienceCBusiness Media Dordrecht 2013
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1 Introduction To determine the average size or size distribution of particle dispersion is a task considerably more complex than it might seem. In the first place because of the ambiguous definition of “size” of an (irregular) particle. In fact, particles are three dimensional objects normally described by three parameters (length, breadth and height) and only spherical particles can be fully described by a single number (its diameter). The strategy usually adopted is to express the particle dimension as an “equivalent spherical diameter”, defined as the diameter of the sphere that generates the same result as that of the particle under observation. Volume based, aerodynamic, electrical mobility, optical or Stokes diameters are just a few examples of normally used equivalent diameters (Fig. 1). This concept leads to the fact that different sizing techniques, based on different measuring principles/properties, may generate different equivalent diameter values for the same particles (the less spherical the particle the greater the difference) [1–5]. Conversely the same equivalent diameter may be obtained for different particles. Although this approach
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