Dynamic light scattering method in studies of silica and gold nanoparticles

Background and Objectives: It is well known, that uncritical use of the dynamic light scattering (DLS) method may give unacceptable results for the volume or number distributions of particles as compared with transmission electron microscopy (TEM) data. The purpose of this study is to investigate application of the DLS method for determining the size of colloidal silica and gold nanoparticles and to compare results of three methods: DLS, TEM, and absorption spectroscopy (see next paper). Materials and Methods: Silica nanoparticles were synthesized by the Stöber method and by the L-arginine method. Gold nanoparticles were synthesized by the Frens method. A Zetasizer Nano ZS instrument (Malvern, UK) and Photocor (Russia) were utilized for DLS measurements. Libra-120 transmission electron microscope (Carl Zeiss, Jena, Germany) at the Simbioz Center for the Collective Use of Research Equipment in the Field of Physical-Chemical Biology and Nanobiotechnology at the IBPPM RAS was utilized for obtaining the TEM images. Results: The average DLS diameters of the silica nanospheres (from 50 to 1000 nm) are shown to be in good agreement with TEM data, whereas DLS size distribution is usually broadened in comparison with TEM data. For strongly scattering gold nanoparticles (GNPs) with a diameter higher than 30–40 nm, deviation of their shape from spherical one and the impact of the rotational diffusion lead to false size peak at about 5–10 nm. For absorbing GNPs with diameters less than 20 nm and weak scattering particles, DLS method often gives a false second peak with larger size in the intensity distribution. The practical methods of solving the problem of false peaks are discussed. For fast estimation of the average size of GNPs in the range of 15–100 nm, the absorption spectroscopy can give reasonable sizes derived from analytical and graphical calibrations (see next paper). For GNPs with a diameter of 3–15 nm, the calibration curve for the size determination is based on the measurement of the ratio between the absorption intensities at the plasmon resonance wavelength and at 450 nm. Conclusion: The relative advantages and drawbacks of three methods (TEM, DLS, and absorption spectroscopy) for silica and gold nanoparticle sizing have been discussed. For spherical particles, the average DLS size are in good agreement with TEM data, whereas the DLS size distribution is typically much broader than that derived from TEM histograms. What is more, DLS size distribution can be greatly affected by the rotational diffusion even for slightly nonspherical particles.