William (Yu Ren) Zhou (SEAS `16, SAS `16), Nicholas J. Kybert

DNA-Functionalized Carbon Nanotube Sensors
William (Yu Ren) Zhou (SEAS ’16, SAS ’16), Nicholas J. Kybert (SAS), A.T. Charlie Johnson (SAS, SEAS)
Department of Physics and Astronomy
Funded by:
Abstract
DNA-functionalized Single-Walled Carbon Nanotube (SWCNT) transistors were investigated as portable and energy-efficient
chemical sensors capable of determining the concentration and identity of analytes (chemicals in the environment). When
analytes bind to DNA molecules, a measurable change in the electrical properties of the sensors is produced. When the
transistor's gate voltage is fixed at -8V, current through the transistor quickly changes when analyte is pulsed through the sensor;
pulsing clean air through the sensor reverses this change. Also, the shapes of current-gate voltage hysteresis curves change
when analytes are pulsed through the sensor.
Theory of Sensor Operation
•  Since both DNA and SWCNTs contain
benzene rings, DNA adheres to SWCNTs
through π-π stacking
Sensing Runs
Experimental Methods
Analytes Tested
Sensor Fabrication
Figure 6: Propionic Acid
Figure 7: DMMP
Results
Figure 8: (+)limonene
•  Gate voltage kept constant at -8V
•  Propionic acid was used as analyte
Figure 1: SWCNT functionalized with DNA molecule
Figure 3: Schematic diagram of sensor
•  Analyte vapor pulsed on/off every 2 minutes
Figure 4: Electrode configuration on chips
•  Analytes in environment reversibly bind to
chemical sites on DNA molecules
•  Sensors were built on substrate of 6-inch p-type silicon wafers which have a thin
layer of electrically insulating SiO2 on either face
•  Because most analytes are polar/charged,
electric fields are established in the vicinity
of the SWCNT
•  Photolithography was used to define the positions where electrodes will be
positioned on substrate
•  Electrical properties of SWCNT are
changed, and these changes can be
measured
•  Wafers were cut into individual rectangular chips
•  Small spread in current change across devices
•  Concentrations as low as 1.3 vol% saturated analyte
vapor were detected
•  Current change generally increased as analyte
concentrations increased
•  Gold electrodes were deposited through evaporation
•  Limitations:
•  Semiconducting SWCNT solution (98% purity) was deposited onto the chips so
that SWCNTs could bridge gap between two electrodes
•  Sensor response saturated at high concentration
Figure 9: Current change vs. time at fixed gate voltage
•  Nature of analyte cannot be identified
•  DNA solution was deposited onto chips in order to functionalize SWCNTs
Applications of Sensor
DNA-functionalized SWCNT sensors have
many important applications, including:
•  Backside of chips were scratched and covered in silver paint for gate electrode
Sensor Testing
•  Cancer detection
•  Airport security
•  Ethanol sensor
•  “Electronic noses” for robots
Figure 2: Photo of
experimental setup for
cancer detection, which
involves sensing
chemicals in patients’
blood plasma.
Figure 5: Schematic diagram of
apparatus used to test sensors.
MFC is an abbreviation for Mass
Flow Controller.
Figure 10: Current vs. gate voltage
hysteresis curves with different %
saturated propionic acid vapor
Figure 11: Current vs. gate voltage
hysteresis curves with different %
saturated (+)limonene vapor
Figure 12: Current vs. gate voltage
hysteresis curves with different %
saturated DMMP vapor
By varying gate voltage, limitations of the fixed gate voltage results were resolved:
•  High concentration responses were distinguishable due to different behaviors of
curves at high gate voltage
•  Nature of analyte can be identified, since different analytes change the shape of
hysteresis curves in different ways