Carbon nanotube field-effect sensors for single-molecule detection

This thesis describes a detection system for single molecules based on individual single-walled carbon nanotube field-effect sensors. The sensitivity, spatial confinement and transducer gain of the sensor is derived from a conductance controlled electrochemically created defect, which is also chemically reactive. An automated microfluidic system is designed to enable long and stable measurements of the carbon nanotube device in aqueous environment with temperature control of ±0.1°C. A probe DNA can be covalently attached to the defect through an amide bond and the conductance is modulated when a target DNA binds to the probe. As a result, the conductance shows a traditional random telegraph signal and fluctuates between a hybridized and melted state. By monitoring the conductance as a function of temperature, the kinetics and thermodynamics can be extracted, which are comparable to previous fluorescent correlation spectroscopy studies using optical fluorescent resonant energy transfer. By studying the fluctuation amplitude as a function of charge proximity, buffer concentration and solution potential, it is shown that the sensor is based on a field-effect. The sensor has a temporal resolution of 200 μs and a signal to noise ratio of 3-8 when continuously measuring for 30 seconds. By further reducing the parasitics, the sensor has the capabilities to detect biomolecule kinetics down to microsecond resolution, which could make it an attractive tool for single-molecule experiments with fast kinetics.