Highly aligned double wall carbon nanotubes (DWCNT) and multi-wall carbon nanotubes (MWCNT) were
synthesized in the shape of towers and embedded into microchannels for use as a biosensor. The towers were
fabricated on a substrate patterned in 1mm x 1mm blocks with 1 mm spacing between the blocks. Chemical vapor
deposition was used for the nanotube synthesis process. Patterned towers up to 8 mm high were grown and easily
peeled off the silicon substrate. A nanotube electrode was then soldered on printed circuit boards and epoxy was cast
into the tower under pressure. After curing, the top of the tower was polished. RF-plasma at 13.56 MHz was used to
enhance the electrocatalytic effect of the nanotube electrode by removing excess epoxy and exposing the ends of the
nanotubes. Au particles were electrodeposited on the plasma treated tower electrode. Cyclic voltammetry (CV) for
the reduction of 6 mM K3Fe(CN)6 (in a 1.0 M KNO3 supporting electrolyte) was performed to examine the redox
behavior of the nanotube tower electrode. Next, a master mold for polydimethylsiloxane (PDMS) was patterned
using SU-8 and then a Pt disk electrode was embedded into the PDMS. The final fluidic channel between the epoxy-nanotube
electrode and PDMS was sealed using a UV-curing adhesive. Impedance between the Pt and nanotube
electrodes was monitored while flowing different solutions and LNCaP prostate cells. The impedance changed in
proportion to the concentration of cells in the solution. A needle-type composite microelectrode was then fabricated
by injecting a carbon nanotube-epoxy solution into a pulled-glass tube. CV and differential pulse voltammetry
(DPV) to detect dopamine were showed a highly linear response with a sensitivity 100 nA/mM. Based on the
impedance results using the flowing cells and the CV and DPV results, carbon nanotube microelectrodes are a
promising candidate for cancer cell detection and neurotransmitter detection.
A multifunctional structural nanoskin is being developed using Carbon Nanosphere Chains (CNSC) and a polymer.
Three suites of properties are particularly important in developing the nanoskin; good elastic properties, good
electrical properties, and good transducer properties. The CNSC material is first studied in the bulk form.
Preliminary results show CNSC are well crystallized graphitic structures with spherical shape connected in chains.
The CNSC are almost catalyst free, and are lightweight and hydrophobic. The CNSC morphology is between that of
spheres and cylinders. Initial testing was done to characterize the CNSC and to determine if the nanosphere chains
can be purified and then dispersed to reinforce an epoxy polymer. The testing involved evaluation of the mechanical
properties and electrical conductivity of an epoxy nanocomposite material. A simple analysis of series and parallel
fiber reinforcement of polymers was performed first and predicted that limited improvement in stiffness is possible
using discontinuous fibers, while a large improvement is possible using continuous fibers. Epoxy nanocomposites
were then formed by simultaneously mixing CNSC and epoxy using a shear mixer and ultrasonicator. The elastic
properties of the cured nanocomposite showed small improvement with small percentages of the CNSC added to the
polymer. On the other hand, compressed CNSC powder has high electrical conductivity. Therefore, a nanoskin
material was designed by dispersing CNSC in a solvent, solution casting the solvent into a thin film in a mold,
covering the film with epoxy, and closing the mold and curing under pressure. Evaluation of the material is still
underway, but the nanoskin has electrical conductivity on one side and is electrically insulating on the other side. A
major advantage of the CNSC material is that is can be produced in large quantities at reasonable cost for many
This paper describes progress in development of a sensor-actuator-nanoskin material based on multi-wall carbon nanotube arrays. This material can have individual sensing, actuation, or reinforcement properties, or the material may have combined multi-functional properties. The sensing and actuation properties are based on the theoretical telescoping property of multi-wall carbon nanotubes. The sensing property has been demonstrated in the literature. The actuation property is modeled in this paper but not demonstrated. Work is described that later may verify the actuation. Nanoskin samples are also fabricated and tested for mechanical, hydrophobicity, and capillarity properties. Overall, synthesis of dense arrays of long multi-wall carbon nanotubes is opening the door for the development of novel sensors, actuators, and multifunctional smart materials.
Highly aligned multi-wall carbon nanotube arrays up to 4 mm tall were synthesized on Si wafers using a chemical vapor deposition process with water delivery. Based on the long nanotube arrays, several prototype smart materials were developed including a biosensor, electrochemical actuator, and nanotube probes. The biosensor was formed by casting epoxy into a nanotube array and polishing the ends of the nanotubes. This electrode produced a near ideal sigmoidal cyclic voltammogram. Nanotube electrodes were then used to form a label-free immunosensor based on electrochemical impedance spectroscopy. The nanotube array immunosensor has good sensitivity, but decreasing the array size and improving the biofunctionalization is expected to dramatically increase the reproducibility and sensitivity. The electrochemical actuator was formed by bonding an electrode to a 1mm square by 4 mm long as-grown nanotube array post. The nanotube array actuator operated up to 10 Hz in a 2 M NaCl solution. With a driving voltage of 2 volts, the actuator produced 0.15% strain. Finally, nanotube bundles are being welded to tungsten tips and put inside glass needles for use as probes for biosensors and electrophysiology applications. All the smart materials applications discussed are recent, and further development is expected to yield improved performance and commodity level practical devices.
This paper discusses the development of new multifunctional smart materials based on Carbon Nanofibers (CNF) and Multi-Wall Carbon Nanotubes (MWCNT). The material properties of CNF/MWCNT are a little lower than the properties of Single Wall Carbon Nanotubes (SWCNT). However, the CNF/MWCNT have the potential for more practical applications since their cost is lower. This paper discusses the development of four CNF/MWCNT-based sensors and actuators. These are: (i) an Electrochemical Wet Actuator for use in a liquid electrolyte, (ii) an Electrochemical Dry Actuator for use in a dry environment, (iii) a Bioelectronic sensor; and (iv) a MWCNT neuron for structural health monitoring. These materials are exciting because of their unique properties and many applications.
The paper discusses the development of polymer composite materials based on carbon nanotubes. Carbon Nanotubes can be used to form polymer hybrid materials that have good elastic properties, piezoresistive sensing, and electrochemical actuation. Of particular interest are smart nanocomposite materials that are strong and self-sensing for structural health monitoring, or self-actuating to improve the performance and efficiency of structures and devices.
Since nanoscale research is broad, challenging, and interdepartmental, undergraduate through Ph.D. level students and
faculty have combined efforts to attack the special problems related to building nanoscale smart materials. This paper gives an overview of the work being performed to manufacture polymer nanocomposite materials starting from nanotube synthesis through to device fabrication and testing. Synthesis is performed using an EasyTube Nanofurnace, functionalization is done using plasma coating, dispersion using rotary mixing and ultrasonication, and processing
using vacuum and pressure casting. Reinforced polymers, a carbon nanotube solid polymer electrolyte actuator, and piezoresistive sensors are being developed for several potential applications. The materials produced indicate that carbon nanotube hybrid smart materials may become a new class of smart material with unique properties and applications, but much work still needs to be done to realize their full potential.