Carbon Nanoelectronic Heterodyne Sensors for Chemical & Biological Detection
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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. 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 nanoelectronic sensing technologies are still incapable of high-fidelity detection critical for studying nanoscale events in complex environments like ligand-receptor binding, molecular adsorption/desorption, stacking, catalysis etc.
In this thesis, I 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 the oscillating dipole moment of a molecule and an alternating current drive voltage which excites it. By detecting molecular dipole rather than the associated charge, we address the limitations of conventional charge-detection based nanoelectronic sensing techniques.
In particular, using a carbon nanotube heterodyne platform, I demonstrate biomolecular detection in high ionic background solution where conventional charge- detection based techniques fail due to fundamental Debye screening effect. Next, we report graphene nanoelectronic heterodyne vapor sensors which can detect a plethora of vapor molecules with high speed (~0.1sec) and high sensitivity (<1ppb) 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 electrical tuning of molecule-graphene binding kinetics by electrostatic control of graphene work function signifying the ability to tailor chemical interactions on-demand.