Conductivity studies of single protein molecules

Zaki, Athraa J. 2016. Conductivity studies of single protein molecules. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

A fundamental step for future uses of biomolecules in electronics is the study of the bonding, orientation and conductance of a single molecule attached to a conductive substrate, which is the building block of electronic materials and devices based on molecular conduction. This work provides an in-depth examination of morphology and electrical properties of different molecules anchored to Au(111) and to sustainable carbon materials (graphite and graphene). Cytochrome b562 (Cyt b562), TEM beta-lactamase and the superfolded green uorescent protein engineered with phenyl azide were exposed to UV irradiation to transform the azide compound into the nitrene radical, which enabled successful molecule linking to graphene. The UV-based approach was tested on the above molecules to ascertain its robustness against the speci�city of the protein used. The e�ciency of the procedure was inspected by imaging via atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). By repeated sample preparation and imaging, we established suitable protein concentrations to enable single-molecule measurements on the resulting samples (e.g., the concentration range optimal for cyt b562 on gold was 0.025-0.5 �M). We used a home-built environmental cell in combination with STM to study the conductance of di�erently engineered cyt b562 proteins on Au(111), as well as the conductance of oligothiophene on gold, under di�erent humidity and temperature conditions. We found that the conductance of cyt b562 is smaller at lower relative humidity and further decreased when also temperature is reduced. Measuring the conductance as a function of the tip-substrate distance in both tip approaching and retracting modes revealed the occurrence of hysteresis. The engineered cyt b562 with two thiols in the long axis led to less hysteresis in the conductance and larger protein height on gold (from AFM) compared to the protein with thiols in the short axis. Our results stress the importance of protein engineering to control the electrical properties of functionalized surfaces. This study meets the growing demand for achieving more e�cient molecule linking to conductive substrates, and studying environmental e�ects on the electrical response of functionalized surfaces (which is relevant, e.g., to sensing applications).

Item Type:	Thesis (PhD)
Date Type:	Publication
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Molecular conduction, Morphology, Sustainable carbon materials, Electrical properties of different molecules anchored to Au(111) scanning tunnelling microscopy, STM, Conductance of oligothiophene on gold
Funders:	Iraqi Government Scholarship
Date of First Compliant Deposit:	7 November 2016
Last Modified:	20 Jul 2017 05:02
URI:	https://orca.cardiff.ac.uk/id/eprint/95883

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