Electrical charge mobility in hydrated bovine serum albumin

Abstract

Charge transport in samples of compressed bovine serum albumin has been investigated up to a hydration level, m, of 8.2 wt % water and the carrier mobility and trapping parameters deduced. A novel method has been employed in which H⁺(H₂O)_n or CO^–₃ and O^–₂ ions were deposited on the free surface of disc samples attached to a grounded metal collector and their subsequent movement into the samples monitored by a non-contacting induction probe. A theory based on multiple hopping of electrons or holes via a series of traps in the sample is used to determine the transport parameters.

The mobility is found to be independent of the sign of the deposited ions, to vary inversely with field in the range 10⁵–10⁷ V m^–1 and with hydration according to a law µ=µ_d exp βm where µ_d≈ 10^–12 to 10^–11 m² V^–1 s^–1 and β= 0.46. The trapping and release parameters also depend strongly on hydration and the surface plays a special role in that while charge does not transfer into the bulk in the dry state, it is increasingly facilitated as hydration increases.