![]() Thus it is necessary to use high power lasers (tens or hundreds of milliwatts) for scattering excitation increasing the size and power consumption of the measuring device. The main limitation of DDRS is the need of measurement of very weak optical signals for registration depolarized component of scattered light (components VH). DRS method was used for measuring geometrical parameters of gold nanoparticles Particle length L and diameter d can be found according to the values of diffusion coefficients using the model of diffusion for particles of a given shape (e.g., cylindrical). ![]() These ACF are connects with the NP translational and rotational diffusion coefficients D t and D r. Then the intensity autocorrelation functions (ACF) G (1) VV(τ) H G (2) VH (τ) are calculated from time dependences of the scattered light intensity, where τ - the delay time of the ACF. The scattered light collection system includes polarization analyzer, which is adjusted successively to two fixed positions, one transmits light with VV polarization, and the other - with VH. Fluctuations decay rates are determined for the light scattered with two different polarizations, one of them (called co-polarized) coincides with the polarization of the exciting radiation (VV), and other (called cross-polarized) - is perpendicular to it (VH). DDRS method use the effect depolarization of linearly polarized light due to scattering on non-spherical particles. Scattered light is collected on nominated angle and time dependence of scattering intensity is measured. Laser beam linearly polarized in the vertical plane (V) are focused in the small volume of sample liquid (less than 1 mm 3). The method is based on the detection of intensity fluctuations of the scattered light by the particles moving under the influence of Brownian motion in a liquid. ![]() Such optical method, as depolarized dynamic light scattering (DDRS), was used in a number of studies for control of the geometric parameters of non-spherical NP. Physico-chemical methods, primarily optical, require relatively inexpensive equipment, substantially less time for the sample preparation and analysis, allows to automate the analysis procedure. For routine measurements such methods have a number of advantages over microscopy: the possibility of NP parameters measurement directly in a liquid, high representativeness of the samples containing large number of NP. But for the routine measurements (including production control in the manufacturing process, the control for compliance of nanosafety) physical and chemical measurement methods are preferred. Aspect ratio (AR) is also of interest for the study of the NP toxic properties, due to strongly influences of AR on particles ability to penetrate biological barriers.ĭifferent types of microscopy, such as SEM, TEM and AFM, can be used for study of the size and shape of non-spherical NP. The efficiency of NP using depends strongly on their shape and size, so it is very important to measure the particle's geometrical parameters: length, diameter, aspect ratio (ratio of length to diameter) at different stages of their synthesis and application. Non-spherical nanoparticles (NP), such as nanorods, nanowires, nanotubes, are used in various fields: in medicine - as fluorescent enhancers, tumor markers, light receptors for photodynamic therapy, in technology - as sources of strong local heating, in electronics - as molecular electronic devices.
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