On the measurement of gold nanoparticle sizes by the dynamic light scattering method

The application of the dynamic light scattering (DLS) method for determining the size distribution of colloidal gold nanoparticles in a range of 1–100 nm is discussed. It is shown that rotational diffusion of nonspherical strongly scattering particles with sizes of larger than 30–40 nm results in the appearance of a false peak in a size range of about 5–10 nm. In this case, the uncritical application of the DLS method may yield particle volume or number size distributions different from those obtained by transmission electron microscopy. For weakly scattering particles with diameters of smaller that 20 nm, the DLS method demonstrates an additional peak of intensity distribution in the region of large sizes that is related to particle aggregates or byproduct particles rather than individual nanoparticles. Practical methods for solving the problem of false peaks are discussed. It is established that the width of the DLS distribution does not correspond to transmission electron microscopy data and is overestimated. The advantages and drawbacks of the methods are compared and it is noted that, at present, the DLS method is the only instrument suitable for nonperturbative and sensitive diagnostics of relatively slow aggregation processes with characteristic times on the order of 1 min. In particular, this method can be used to diagnose gold nanoparticle conjugate aggregation initiated by biospecific interactions on their surface.