Experimental Evidence of Strong Anomalous Diffusion in Living Cells

We show that transport of polymeric particles within living cancer cells exhibits strongly anomalous diffusion. Particle motion demonstrated super-diffusion, indicating active cellular transport of particles likely due to molecular motors. We also calculated a range of time-dependent displacement moments and extracted scaling exponents\textit{ $\lambda $}($q)$ for each moment order $q$. Those were non-linear with $q$, indicating non-scale-invariant motion. Also, \textit{$\lambda $}($q)$/$q$ was non-decreasing, fulfilling conditions for strong anomalous diffusion, presented here experimentally for the first time. Specifically, \textit{$\lambda $}($q)$ exhibited bi-linearity, with slopes of $\sim $0.6 and $\sim $0.8 at low and high $q$-values. That bi-linearity indicates that particle motion is composed of sub-diffusive regimes separated by active flights; those were sub-ballistic and not separable using a directionality criterion. We suggest that sub-ballistic flights are associated with the small particles used in this work (100-200 nm); those diffuse through the cytoplasm while being actively transported. Results are discussed in terms of particle interactions with their microenvironment and its dynamics.