Slow and remanent electric polarization of adsorbed BSA layer evidenced by neutron reflection

Using neutron reflectivity together with an appropriate electrochemical cell, we have studied the effects of transverse electric field on the bovine serum albumin (BSA) monolayer initially adsorbed at the interface of the aqueous solution and a conductive doped-silicon wafer. Depending on the sign of the initial potential, a second layer is adsorbed, or not, on top of the first whereas a subsequent reversal of potential has no effect. We show that this behaviour reveals the slow and remanent electric polarization of the first BSA layer. Based on the permanent dipolar structure of BSA, we suggest an analogy with dipolar glasses that may account for the slowness and memory of the process.