Temperature and force dependence of nanoscale electron transport via the Cu protein Azurin

TL;DR

This study investigates how temperature and applied force influence electron transport in Azurin proteins at the nanoscale, revealing that mechanical stress can alter the transport mechanism and emphasizing the importance of controlling force during measurements.

Contribution

It demonstrates that the electron transport mechanism in Azurin proteins depends on applied force and temperature, highlighting the role of mechanical stress in nanoscale electron transport.

Findings

ETp mechanism shifts from temperature-independent to thermally activated with increased force

Holo-Az and apo-Az show different responses to force and temperature

Stress control is crucial for accurate ETp measurements in flexible systems

Abstract

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), 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.