Electrochemical gating enhances nearfield trapping of single metalloprotein junctions

Abstract

Metalloprotein based junctions are widely used as model systems in the field of molecular bioelectronics to miniaturise electronic circuitry with help of biomolecular device components. To further progress in the field, new approaches are sought to form junctions with longer lifetimes than the current limit of hundreds of milliseconds, ideally approaching timescales sufficient for detailed junction characterization or even relevant for device operation. Here, we present an electrochemically gated plasmon-supported break-junction (EC-PBJ) platform that prolongs the lifetime of single-molecule junctions of Azurin (Azu) under strict electrochemical control and physiological conditions. EC-PBJ efficiently combines nearfield and electrochemical gating effects that stabilise the formed metalloprotein junction while maintaining the native structure of the biomolecule. For moderate far-field power densities of ca. 9.49 mW μm⁻², the lifetime of individual oxidised Azu junctions is increased by a factor of 40 compared to laser-OFF conditions, which equals a nearfield trapping efficiency increase close to three orders of magnitude compared with reduced Azu junctions at the lowest used power density. We ascribe the lifetime tuning through EC-PBJ to two synergistic parameters: (i) the control of the redox state of trapped Azu that affects its resonant state and polarisability, and (ii) the steering of the localised surface plasmon resonance (LSPR) of the junction nanogap through electrode potential control. At the used laser mid-power range, the Azu redox state and polarisability have a more significant effect on the nearfield trapping efficiency than the LSPR shift. Non-invasively increased junction lifetimes pave the way for the development of improved biomolecular sensing and recognition platforms.