Confined diffusion is ubiquitous in nature. Ever since the "anomalous yet 0 Brownian" motion was observed, the non-Gaussianity in confined diffusion has been unveiled as an important issue. In this Letter, we experimentally investigate the characteristics and source of non-Gaussian behavior in confined diffusion of nanoparticles suspended in polymer solutions. A time-varied and size-dependent non-Gaussianity is reported based on the non-Gaussian parameter and displacement probability distribution, especially when the nanoparticle's size is smaller than the typical polymer mesh size. This non-Gaussianity does not vanish even at the long-time Brownian stage. By inspecting the displacement autocorrelation, we observe that the nanoparticle-structure interaction, indicated by the anticorrelation, is limited in the short-time stage and makes little contribution to the non-Gaussianity in the long-time stage. The main source of the non-Gaussianity can therefore be attributed to hopping diffusion that results in an exponential probability distribution with the large displacements, which may also explain certain processes dominated by rare events in the biological environment.

http://dx.doi.org/10.1021/acs.jpclett.5b02624

The authors acknowledge the National Natural Science Foundation of China (11572335, 11272321, and 11202219) and the Ministry of Science and Technology (2011CB707604) for financial support. And we are grateful to the fruitful discussions with Dr. P-Y Jin.

Xue CD,Zheng X,Chen KK,et al. Probing Non-Gaussianity in Confined Diffusion of Nanoparticles[J]. JOURNAL OF PHYSICAL CHEMISTRY LETTERS,2016,7(3):514-519.