Scaling in diffusive transport through membranes

Size-selectivity and anomalous subdiffusion of nanoparticles through carbon nanofiber-based membranes

A simulation is presented here that serves the dual functions of generating a nanoporous membrane replica and executing the Brownian motion of nanoparticles through the virtual membrane. Specifically, the concentration profile of a dilute solution of fluorescent particles in a stochastic and SiO(2)-coated carbon nanofiber (oxCNF), nanoporous membrane was simulated. The quality of the simulated profile was determined by comparing the results with experimental concentration profiles. The experimental concentration profiles were collected adjacent to the oxCNF membrane surface from time-lapse fluorescence microscopy images. The simulation proved ideal as an accurate predictor of particle diffusion-the simulated concentration profile merged with the experimental profiles at the inlet/exit surfaces of the oxCNF membrane. In particular, the oxCNF barrier was found to hinder the transport of 50 and 100 nm particles and transmembrane trajectories were indicative of anomalous subdiffusion; the diffusion coefficient was found to be a function of time and space.

Molecular transport in a crowded volume created from vertically aligned carbon nanofibres: a fluorescence recovery after photobleaching study

Rapid and selective molecular exchange across a barrier is essential for emulating the properties of biological membranes. Vertically-aligned carbon nanofibre (VACNF) forests have shown great promise as membrane mimics, owing to their mechanical stability, their ease of integration with microfabrication technologies and the ability to tailor their morphology and surface properties. However, quantifying transport through synthetic membranes having micro- and nanoscale features is challenging. Here, fluorescence recovery after photobleaching (FRAP) is coupled with finite difference and Monte Carlo simulations to quantify diffusive transport in microfluidic structures containing VACNF forests. Anomalous subdiffusion was observed for FITC (hydrodynamic radius of 0.54 nm) diffusion through both VACNFs and SiO(2)-coated VACNFS (oxVACNFs). Anomalous subdiffusion can be attributed to multiple FITC-nanofibre interactions for the case of diffusion through the VACNF forest. Volume crowding was identified as the cause of anomalous subdiffusion in the oxVACNF forest. In both cases the diffusion mode changes to a time-independent, Fickian mode of transport that can be defined by a crossover length (R(CR)). By identifying the space-and time-dependent transport characteristics of the VACNF forest, the dimensional features of membranes can be tailored to achieve predictable molecular exchange.