Anomalously Slow Diffusion in Protein-Coated Nanopores

Peanut protein Ara h 1 is detected by the change in electrical conductivity through an Au-coated nanoporous polycarbonate membrane sensor onto which the peanut antibody is immobilized. Introduction of peanut protein Ara h 1 causes a reduction in the membrane conductivity by binding to antibodies immobilized onto the pore walls, reducing the effective pore diameter. The observed conductivity changes are studied as a function of time and protein concentration, and these results depend strikingly on the nominal pore diameter. For 15 nm diameter pores, the conductivity change saturates at low peanut protein concentration, with no significant time lag in the sensor response. For 30 and 50 nm diameter pores, a time lag of tens of miutes is observed in the sensor response that appears to be consistent with mass transport limitations. However, back-of-the-envelope calculations sugest that transport through these membranes should not be rate-limting. These calculations quantitatively include the effects of hindered transport, as described by the Renkin equation. These results demonstrate that axial protein diffusion is anomalously slow within these protein-coated nanoporous membranes.