Wenjie Li, Lior Sepunaru, Nadav Amdursky, Sidney R. Cohen, Israel Pecht, Mordechai Sheves, David Cahen
We report conducting probe atomic force microscopy (CP-AFM) measurements of electron transport (ETp), as a function of temperature and force, through monolayers of holo-azurin (holo-Az) and Cu-depleted Az (apo-Az) that retain only their tightly bound water, immobilized on gold surfaces. The changes in CP-AFM current-voltage (I-V) curves for holo-Az and apo-Az, measured between 250 - 370K, are strikingly different. While ETp across holo-Az at low force (6 nN) is temperature-independent over the whole examined range, ETp across apo-Az is thermally activated, with calculated activation energy of 600\pm100 meV. These results confirm our results of macroscopic contact area ETp measurements via holo- and apo-Az, as a function of temperature, where the crucial role of the Cu redox centre has been observed. While increasing the applied tip force from 6 to 12 nN did not significantly change the temperature dependence of ETp via apo-Az, ETp via holo-Az changed qualitatively, namely from temperature-independent at 6 nN to thermally activated at forces \geq 9 nN, suggesting changes in the protein structure upon increasing the applied force. The capability of exploring ETp by CP-AFM over a significant range of temperatures, with varying tip force to detect possible pressure-induced changes in the sample, significantly adds to the ability to study ETp through proteins and of using ETp to study proteins, with this approach.
View original:
http://arxiv.org/abs/1207.5202
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