Single-molecule electrochemical imaging resolves the midpoint potentials of individual fluorophores on nanoporous antimony-doped tin oxide

05 June 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We report reversible switching of oxazine, cyanine, and rhodamine dyes by a nanoporous antimony-doped tin oxide electrode that enables single-molecule (SM) imaging of electrochemical activity. Since the emissive state of each fluorophore is modulated by electrochemical potential, the number of emitting single molecules follows a sigmoid function during a potential scan, and we thus optically determine the formal redox potential of each dye. We find that the presence of redox mediators (phenazine methosulfate and riboflavin) functions as an electrochemical switch on each dye’s emissive state and observe significantly altered electrochemical potential and kinetics. We are therefore able to measure optically how redox mediators and the solid-state electrode modulate the redox state of fluorescent molecules, which follows an electrocatalytic (EC’) mechanism, with SM sensitivity over a 900 µm2 field of view. Our observations indicate that redox mediator-assisted SM electrochemical imaging (SMEC) could be potentially used to sense any electroactive species. Combined with SM blinking and localization microscopy, SMEC imaging promises to resolve the nanoscale spatial distributions of redox species and their redox states, as well as the electron transfer kinetics of electroactive species in various bioelectrochemical processes.

Keywords

electrocatalytic (EC') mechanism
molecular electrochemistry
redox-active fluorescent probes
redox mediators
transparent nanoporous electrode

Supplementary materials

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Supplementary Figures
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supplementary figures with additional discussions
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Movie S1. SMEC imaging of ATTO655 dye molecules
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SMEC imaging of ATTO655 dye molecules captured during an electrochemical potential sweep between 0 V and –0.8 V at a scan rate of 0.1 V/s in 1 M NaNO3 solution. Scale bar: 5 μm.
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Movie S2. SMEC imaging of AF647 dye molecules
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SMEC imaging of AF647 dye molecules captured during an electrochemical potential sweep between –0.5 V and –1.0 V at a scan rate of 0.1 V/s in 1 M NaNO3 solution. Scale bar: 5 μm.
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Movie S3. SMEC imaging of ATTO647N dye molecules
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SMEC imaging of ATTO647N dye molecules captured during an electrochemical potential sweep between –0.5 V and –1.1 V at a scan rate of 0.1 V/s in 1 M NaNO3 solution. Scale bar: 5 μm.
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