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%DIFDELCMD < \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 .
The mechanisms of solid-state electron transport (ETp) via a monolayer of immobilized Azurin (Az) was examined by conducting probe atomic force microscopy (CP-AFM) , both as function of temperature ( 248 - 373K) and of applied tip force (6-12 nN). By varying both temperature and force in CP-AFM, we find that the ETp mechanism can alter with a change in the force applied via the tip to the proteins. As the applied force increases, ETp via Az changes from temperature-independent to thermally activated at high temperatures. This is in contrast to the Cu-depleted form of Az ( apo-Az %DIFDELCMD < \pm100 %%% ), where increasing the applied force causes only small quantitative effects, that fit with a decrease in electrode spacing. At low force ETp via holo-Az is temperature-independent and thermally activated via apo-Az. This observation agrees with macroscopic-scale measurements, thus confirming that the difference in ETp dependence on temperature between holo- and apo-Az is an inherent one that may reflect a difference in rigidity between the two forms. An important implication of these results, which depend on CP-AFM measurements over a significant temperature range , is that for ETp measurements on floppy systems, such as proteins, the stress applied to the sample should be kept constant or, at least controlled during measurement .
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We report
The mechanisms of solid-state electron transport (ETp) via a monolayer of immobilized Azurin (Az) was examined by
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measurements of electron transport (ETp), as a
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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
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I-V) curves for holo-Az and apo-Az, measured between 250
248
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370K, are strikingly different. While ETp across holo-Az at low force (6 nN) is
373K) and of applied tip force (6-12 nN). By varying both temperature and force in CP-AFM, we find that the ETp mechanism can alter with a change in the force applied via the tip to the proteins. As the applied force increases, ETp via Az changes from
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over the whole examined range, ETp across
to thermally activated at high temperatures. This is in contrast to the Cu-depleted form of Az (
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is thermally activated , with calculated activation energy of 600
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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
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tip force from 6 to 12 nN did not significantly change the temperature dependence of ETp via apo-Az,
force causes only small quantitative effects, that fit with a decrease in electrode spacing. At low force
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changed qualitatively, namely from
is
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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
and thermally activated via apo-Az. This observation agrees with macroscopic-scale measurements, thus confirming that the difference in ETp dependence on temperature between holo- and apo-Az is an inherent one that may reflect a difference in rigidity between the two forms. An important implication of these results, which depend on
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measurements
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range of temperatures, with varying tip force to detect possible pressure-induced changes in the sample
temperature range
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significantly adds to the ability to study ETp through proteins and of using ETp to study proteins, with this approach
is that for ETp measurements on floppy systems, such as proteins, the stress applied to the sample should be kept constant or, at least controlled during measurement