Development of novel electrical characterization methods and measurements of G4-DNA and DNA Derivatives

TL;DR

This research develops new electrical characterization techniques for G4-DNA molecules, revealing their charge transport properties and introducing a novel stencil lithography method for better electrical contact formation.

Contribution

It introduces a new electrical measurement approach for G4-DNA and a reversible electrostatic clamping technique for improved contact fabrication.

Findings

Tetra-molecular G4-DNA is twice as polarizable as intra-molecular G4-DNA.

Reproducible conductance of tens to over 100 pA was measured over 10-100 nm distances.

The charge transport follows a thermally activated hopping mechanism.

Abstract

This dissertation presents an investigation into the electrical properties of two types of G4-DNA and several DNA-based molecules, targeting them as candidates for molecular wires and devices. Atomic force microscopy (AFM) and electrostatic force microscopy (EFM) comparison of co-deposited tetra- and intra-molecular G4-DNA reveals variations in morphology and different sensitivity to the applied electric field, suggesting that the folding orientation of the strands affects the molecular structure, i.e. either the tetrad unit or the tetrad-tetrad stacking or both, and therefore the charge mobility. Tetra-molecular G4-DNA is found to be twice as polarizable as intra-molecular G4-DNA, suggesting it has greater charge mobility. These promising results motivated direct electrical transport measurements on tetra-molecular G4-DNA using a special conductive AFM setup, profiling the conductance along the molecule. Reproducible currents of tens to over 100 pA were measured in many tetra-molecular G4-DNA molecules over distances ranging from tens to over 100 nm. The measured charge transport is compatible with long-range thermally activated hopping between multi-tetrad segments. To form the stationary electrical contact, a new variant of stencil lithography was developed, based on reversible electrostatic clamping, overcoming indeterminate blurring effects associated with the problem of metal penetration in standard mask patterning techniques. This method enabled to demonstrate full mask compliance in scanning electron microscopy (SEM) and AFM measurements. The pull-in instability was demonstrated inside an SEM chamber and was confirmed by a non-linear transient response computation. New mechanisms were proposed for the replica formation and the blurring effect based on cluster evaporation and mobile source decay, explaining the ultimate resolution of the masking technique and its limitations.