Novel Method and Device for High Resolution and Quantitative Sizing of Nanoparticles Suspended in Liquids
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Novel Method and Device for High Resolution and Quantitative Sizing of Nanoparticles Suspended in Liquids Axel F. Zerrath, James E. Farnsworth, Jacob H. Scheckman, Jonathan S. Higgins, Erik Willis TSI Incorporated, Shoreview, MN, 55126, U.S.A. ABSTRACT A new technology to size nanoparticles in liquids is presented. The technique is based on aerosol technology coupled to a nanoparticle nebulizer. This allows number concentration measurements in the size range ca. 5 to 500 nm with high peak resolution. INTRODUCTION Determining the size and concentration of nanoparticles in suspensions can be challenging especially when multiple particle diameters are present. Common techniques typically depend on the knowledge of particle and liquid properties such as refractive indices or densities. Mathematical algorithms are often used in these techniques to calculate size distributions based on assumed parameters, assumed distribution curve shape or user-input [1]. Aerosol technology offers material-independent sizing of nanoparticles based on the physical principle that the ability of a particle to traverse an electric field (electrical mobility) is fundamentally related to particle diameter [2]. The Differential Mobility Analyzer (DMA) is the technical implementation of this physical principle, and forms the basis for a series of highresolution instrumentation, including the scanning mobility particle spectrometer, or SMPS. Combined with a single-particle counter, the particle concentration in the discrete size fractions provided by the DMA can be accurately determined. A size distribution is built by scanning numerous size fractions. The single-particle counters used in the aerosol research field are based on a condensation principle (Condensation Particle Counter, CPC). The air stream containing dry particles is mixed with alcohol or water vapor, which is condensed in a subsequent step on the particles to grow these to droplets. The droplets are then focused into simple laser optics whose sole purpose is to count the particles in the air stream. Combining this well-established aerosol technology with a nanoparticle nebulizer, which transfers the particles suspended in liquids into an aerosol, or particles suspended in air, the technology can be applied to sizing and counting particles in liquid suspensions. The key advantage of the described aerosol technology (DMA-CPC) is that the size distribution data is built from counting particles in discrete size channels, whereas ensemble methods (e.g., light scattering), extract the distribution from the combined signal of all particles in the viewing volume [1]. This paper describes the operation principle of the aerosol method, its application to liquid sample analysis, and its advantages on the basis of various examples. THEORY The TSI Model 3485 Nanoparticle Nebulizer is a highly-automated precision nebulizer designed to generate particles from a liquid suspension. The Nanoparticle Nebulizer can be used as a standalone instrument suitable for a variety of research applications, in
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