By controllably probing a biomolecule with a conductive probe AFM tip or scanning tunnelling microscope probe, its conductance characteristics can be controllably analysed. During the past ten years (2000-2010) the group have demonstrated not only a reliable means of conductance assessment, but also an ability to gate conductance by controllably opening up current pathways across the redox site within a number of protein molecules.
Theoretical simulations of this process have enabled the establishment of an understood correlation between the mechanical properties of the molecule and its measured ability to mediate the passage of electrons. These molecular analyses are currently continuing with highly photoresponsive biomolecules (see below). Work by the Group has also demonstrated a correlation between the strength of redox site-electrode electronic coupling (rate of electron transfer) and the magnitude of conductance switching on gating.
The retinal binding protein, bacteriorhodopsin (bR) exhibits good thermal stability and a photostability that vastly exceeds that of synthetic analogues. It also possesses significantly higher photodetection capabilities than any known synthetic analogue (conversion of incident sunlight to chemical energy occurs with 15% efficiency; quantum efficiency is > 60% in H. salinarium). In a collaborative program with Professor Tony Watts in Oxford, we have been able to demonstrate that the protein can be stripped of its lipid and controllably interfaced with transparent electrodes in the formation of monolayer films which generate highly wavelength specific photocurrents of a greater magnitude that prior reported. Moreover, we have been able to probe the charge flow through and electrostatics of single bacteriorhodopsin molecules and to show that these measurable properties are photoswitchable (“the single molecule pixel”). Potential applications to data storage and energy capture are considerable (the wavelength window of protein response is tuneable chemically or through directed evolution).
Bacteriorhodopsin (BR) is a uniquely photoresponsive biomolecule with potential applications in data storage, imaging, and sensing. Uniformly orientated, anchored, largely lipid-free, and active monolayers of BR on metallic electrodes are generated by a facile method.
Using non-invasive Kelvin probe force microscopy, it is possible to measure the light-induced unidirectional proton accumulation at the extracellular protein surface at truly molecular scales.
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