Size Distribution of Nanoparticles in Solution Characterized by Combining Resonance Light Scattering Correlation Spectroscopy with the Maximum Entropy Method.

A single-nanoparticle detection method is reported for characterizing the size distribution of noble metal nanoparticles in solution by combining resonance light scattering correlation spectroscopy (RLSCS) with the maximum entropy method (MEM). The principle of RLSCS is based on the autocorrelation analysis of the resonance light scattering (RLS) fluctuations due to Brownian motion of a single nanoparticle in a highly focused detection volume (less than 1.0 fL), which resembles fluorescence correlation spectroscopy (FCS). However, RLS intensity of nanoparticles such as gold nanoparticles (GNPs) is proportional to the sixth power of sizes according to the Mie theory, which is different from the optical properties of fluorescent molecules. Herein the present FCS theoretical model cannot be directly applied in RLSCS to characterize GNPs. In this study, we used GNPs as model samples and first established an RLSCS theoretical model for the size distribution of GNPs by using the maximum entropy method (MEM), which is called MEM-RLSCS. This model covers the contribution of single-particle brightness of GNPs to the MEM fitting process based on the Mie theory. Then we preformed computer simulations of this model. The simulated results documented that the model proposed was able to well describe the diffusion behaviors and size distribution of nanoparticles. We investigated the effects of certain factors such as size difference, the relative concentration, and single-particle brightness on the size distribution. Finally, we used the MEM-RLSCS for characterization of GNPs in solution, and the results obtained were in agreement with the size distribution of GNPs from transmission electron microscopy (TEM). This method is also suitable for characterization of other metal nanoparticles (such as silver nanoparticles) in solution and in situ study diffusion dynamics of nanoparticles in living cells.