Carbon Nanoelectronic Heterodyne Sensors : A New Paradigm for Chemical and Biological Detection.

Abstract

In 1959, in his famous talk ‘There is plenty of room at the bottom’, physicist Richard Feynman had envisaged a new era of science where one could build electronic systems which would sense and interact with a world only a few atoms in size. To build such systems we not only need new materials but also new transduction strategies. The hunt for new materials has led us back to carbon, a material known since antiquity. Carbon nanotube and graphene-two allotropes of carbon, possess structural, electronic, optical and mechanical properties perfect for building fast, robust and sensitive nano-systems. However, the available sensing technologies are still incapable of high fidelity detection critical for studying nanoscale events in complex environments like ligand-receptor binding, molecular adsorption/desorption, π-π stacking, catalysis, etc. In this thesis, I first introduce a fundamentally new nanoelectronic sensing technology based on heterodyne mixing to investigate the interaction between charge density fluctuations in a nanoelectronic sensor caused by oscillating dipole moment of molecule and an alternating current drive voltage which excites it. By detecting molecular dipole instead of associated charge, we address the limitations of conventional charge-detection based nanoelectronic sensing techniques. In particular, using a carbon nanotube heterodyne platform, I demonstrate for the first time, biological detection in high ionic background solutions where conventional charge-detection based techniques fail due to fundamental Debye screening effect. Next, we report the first graphene nanoelectronic heterodyne vapor sensors which can detect a plethora of vapor molecules with high speed (~ 0.1 second) and high sensitivity (< 1 part per billion) simultaneously; recording orders-of-magnitude improvement over existing nanoelectronic sensors which suffer from fundamental speed-sensitivity tradeoff issue. Finally, we use heterodyne detection as a probe to quantify the fundamental non-covalent binding interaction between small molecules and graphene by analyzing the real-time molecular desorption kinetics. More importantly, we demonstrate for the first time, electrical tuning of molecule-graphene binding kinetics by electrostatic control of graphene work function signifying the ability to tailor chemical interactions on-demand. Our work not only lays a foundation for next-generation of rapid and sensitive nanoelectronic detectors, but also provides an insight into the fundamental molecule-nanomaterial interaction.