Abstract
Measurement of electron transfer at single-molecule level is normally restricted by the detection limit of faraday current, currently in a picoampere to nanoampere range. Here we demonstrate a unique graphene-based electrochemical microscopy technique to make an advance in the detection limit. The optical signal of electron transfer arises from the Fermi level-tuned Rayleigh scattering of graphene, which is further enhanced by immobilized gold nanostars. Owing to the specific response to surface charged carriers, graphene-based electrochemical microscopy enables an attoampere-scale detection limit of faraday current at multiple individual gold nanoelectrodes simultaneously. Using the graphene-based electrochemical microscopy, we show the capability to quantitatively measure the attocoulomb-scale electron transfer in cytochrome c adsorbed at a single nanoelectrode. We anticipate the graphene-based electrochemical microscopy to be a potential electrochemical tool for in situ study of biological electron transfer process in organelles, for example the mitochondrial electron transfer, in consideration of the anti-interference ability to chemicals and organisms.
Highlights
Background noiseRed Oxd A m–2 –2–4 0.139 0.14 0.141 0.142 0.143 Potential (V) EventsElectron transfer numberFigure 3e displays CVs of multiple gold nanostars (GNS) extracted from the current density movie, and similar shapes are presented among these GNS in spite of some small deviations in the amplitudes of oxidation and reduction peaks due to their heterogeneity
We develop a unique graphene-based electrochemical microscopy (GEM) technique that makes a straightforward advance in the detection limit
Using GEM, we successfully show the potential to measure electron transfer in single cytochrome c molecules, which is an essential redox protein involved in the mitochondrial electron transfer
Summary
Background noiseRed Oxd A m–2 –2–4 0.139 0.14 0.141 0.142 0.143 Potential (V) EventsElectron transfer numberFigure 3e displays CVs of multiple GNS (labeled with 1–5) extracted from the current density movie, and similar shapes are presented among these GNS in spite of some small deviations in the amplitudes of oxidation and reduction peaks due to their heterogeneity. The CV of GNS shows ~10 times larger peak current density and a higher signal-to-noise ratio than that of graphene We attribute it to the higher surface area of GNS, which offers more adsorption sites for reactive molecules. It is well known that noble metals will give better electron transfer kinetics than graphene surfaces for inner-sphere redox couples, driven by the local density of states of the electrode near its Fermi level and the reorganization energy of the molecules[43,44]. Such better electron transfer kinetics induces a faster accumulation of charges on the surface of GNS. A faster change in the scattering intensity is observed
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