Towards simultaneous electrical and optical detection of single biomolecules

Abstract

The aim of this thesis is the development of microscopy-compatible electronic devices to advance the field of biosensing in two main directions. First, the development of a platform that allows electrical and optical studies of membrane proteins at the single molecule level. We have fabricated InAs nanowire field-effect transistors and PEDOT:PSS organic electrochemical-transistors on 170 μm thick glass slides for their integration with fluorescence microscopes. Each electronic device was fabricated at the bottom of a circular well sealed with a lipid bilayer. A wide range of membrane proteins can be inserted into this lipid bilayer, most of which work as pores or active pumps for the transport of ions across the membrane. This platform allows simultaneous electrical and optical studies of such proteins, achieving single-molecule resolution when a single protein is inserted in the bilayer. We present the fabrication procedures for these devices and the creation of a lipid membrane over them, as well as electrical characterization and ion sensitivity measurements. The development of novel hardware to achieve electrical contact with the devices while performing fluorescence microscopy is also presented. We demonstrate the viability of our platform via the correlation of electrical and optical signals in response to ion concentration and lipid bilayer rupture. We also present a computational model that provides insight into this system and propose future optimization steps towards the incorporation of membrane proteins into the system. Second, the creation of a sensor that allows electrical detection of a moving target at the single molecule level. In this thesis, we present a theoretical model to determine the feasibility of detecting an actin filament or microtubule passing in close proximity to a carbon nanotube field-effect transistor. This platform would allow the detection of moving biomolecules without the need to physically attach the molecules to the electronic devices. Our results showed that electrical detection is possible given the right experimental conditions. This would enable tracking of large numbers of molecules at once, an important advance for applications where the detection of biological agents is relevant, such as biocomputation.